WO2020225171A1

WO2020225171A1 - Downlight with homogeneous light emission using fdm printed light guides

Info

Publication number: WO2020225171A1
Application number: PCT/EP2020/062237
Authority: WO
Inventors: Johannes Petrus Maria Ansems; Rifat Ata Mustafa Hikmet
Original assignee: Signify Holding B.V.
Priority date: 2019-05-07
Filing date: 2020-05-04
Publication date: 2020-11-12

Abstract

A light guide (1) for use in a lighting device (1000). The light guide (1) comprises a plurality of elongated structures (1202), each elongated structure (1202) having an elongated structure surface (1213) between a first structure part (1211) and a second structure part (1212), the first structure parts (1211) together defining an edge face (1251) of the waveguide (1). Each elongated structure (1202) has a structure height (HI) and a structure width (Wl). Each elongated structure (1202) comprise curvatures (B) in a plane (P) perpendicular to the structure height (HI), the curvatures (B) having radii (r). The radii (r) and the structure width (Wl) are chosen such that radiation (11) propagating through the elongated structure (1202) from the first structure part (1211) to the second structure part (1212) can escape from the elongated structure (1202) via the elongated structure surface (1213) at one or more of the curvatures (B).

Description

DOWNLIGHT WITH HOMOGENEOUS LIGHT EMISSION USING FDM PRINTED LIGHT GUIDES

FIELD OF THE INVENTION

The invention relates to a light guide for use in a lighting device, to a lighting device comprising such a light guide, and to a method for manufacturing such a light guide by means of fused deposition modelling.

BACKGROUND OF THE INVENTION

Luminaires provided by a method including 3D printing are known in the art. US2018/0236712, for instance, describes a method comprising 3D printing a 3D item, the method comprising depositing during a printing stage 3D printable material and an optical fiber, to provide the 3D item with the optical fiber at least partly embedded in 3D printed material, wherein the 3D printable material during at least part of the printing stage comprises a light transmissive material, the method further comprising providing during the printing stage a light escape part comprising 3D printed material comprising the light transmissive material, where visible light propagating through the optical fiber can escape from the optical fiber via the 3D printed material comprised by the light escape part to external of the 3D item.

SUMMARY OF THE INVENTION

Downlights may e.g. be equipped with a LED strip mounted at the circumference. Especially, this may be relevant when the downright has to be relatively thin as it appears favorable to make the height (or thickness) of the downright as small as possible with a high efficiency and a homogeneous illuminance distribution of the exit window. For instance, a lightguide plate with outcouple structures could be proposed to make this possible. However, such solution may be expensive. Further, such solution may not be easy to digitalize the process as it may have to be e redesigned for different sizes. For non- rotational shapes this lightguide solution may be relatively difficult or even impossible. Further, it appears that a relatively high illuminance close to the LEDs and a dark area in the center may be observed, e.g. for rotational shapes. Hence, herein an alternative solution is proposed wherein a specific 3D printing methodology may be applied. Therefore, it is an aspect of the invention to provide an alternative 3D printing method and/or 3D (printed) item which preferably further at least partly obviate(s) one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Within the next 10-20 years, digital fabrication will increasingly transform the nature of global manufacturing. One of the aspects of digital fabrication is 3D printing. Currently, many different techniques have been developed in order to produce various 3D printed objects using various materials such as ceramics, metals and polymers. 3D printing can also be used in producing molds which can then be used for replicating objects.

For the purpose of making molds, the use of polyjet technique has been suggested. This technique makes use of layer by layer deposition of photo-polymerisable material which is cured after each deposition to form a solid structure. While this technique produces smooth surfaces the photo curable materials are not very stable, and they also have relatively low thermal conductivity to be useful for injection molding applications.

The most widely used additive manufacturing technology is the process known as Fused Deposition Modeling (FDM). Fused deposition modeling (FDM) is an additive manufacturing technology commonly used for modeling, prototyping, and production applications. FDM works on an "additive" principle by laying down material in layers; a plastic filament or metal wire is unwound from a coil and supplies material to produce a part. Possibly, (for thermoplastics for example) the filament is melted and extruded before being laid down. FDM is a rapid prototyping technology. Other terms for FDM are “fused filament fabrication” (FFF) or“filament 3D printing” (FDP), which are considered to be equivalent to FDM. In general, FDM printers use a thermoplastic filament, which is heated to its melting point and then extruded, layer by layer, (or in fact filament after filament) to create a three-dimensional object. FDM printers are relatively fast, low cost and can be used for printing complicated 3D objects. Such printers are used in printing various shapes using various polymers. The technique is also being further developed in the production of LED luminaires and lighting solutions.

Amongst others, to solve the issue of a relative high intensity at the edges and a relatively low intensity in the middle, and/or to solve inhomogeneous outcoupling, it is herein suggested to use fused deposition modelling (FDM) to print transparent lines (of light transparent 3D printed material). Such lines may comprise bends to act as leaky lightguides so that the light from the LEDs can be redirected towards the center to obtain homogeneous light extraction. This wavy (bent) lines are area filling and helps to fill a circular area uniformly with decreasing bending radius from sides to the center so that illuminance at the exit window is uniform. It also possible to use light scattering and wedge-shaped light guides (thickness of the light guide decreasing from the edge to the center) for obtaining uniform light extraction. Hence, amongst others printing lines are herein suggested which run from the edges towards the center. In order to obtain uniform illumination, the lines which act as light guides are not straight but have bends. Bending of a lightguide may increase the numerical aperture of this guide and will initiate leakage.

A method for producing a 3D item by means of fused deposition modelling comprises a 3D printing stage comprising layer-wise depositing an extrudate comprising 3D printable material, to provide the 3D item comprising 3D printed material, wherein the 3D item comprises one or more layers (especially a plurality of layers) of 3D printed material. Further, especially the method comprises: providing during the 3D printing stage one or more, especially a plurality, of 3D printed elongated structures (“structures”), each comprising 3D printed material, a first structure part, a second structure part, and an elongated structure surface between the first structure part and the second structure part, wherein at least part of the 3D printed material of the (one or more) elongated structures is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation. Further, especially one or more of (a) a shape of one or more of the (one or more) elongated structures and (b) the elongated structure surface of one or more of the (one or more) elongated structures are chosen such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface. Hence, especially the invention provides a method for producing a 3D item by means of fused deposition modelling, the method comprising a 3D printing stage comprising layer-wise depositing an extrudate comprising 3D printable material, to provide the 3D item comprising 3D printed material, wherein the 3D item comprises one or more layers (especially a plurality of layers) of 3D printed material, wherein the method comprises: providing during the 3D printing stage a plurality of 3D printed elongated structures, each comprising 3D printed material, a first structure part, a second structure part, and an elongated structure surface between the first structure part and the second structure part, wherein the 3D printed material is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein one or more of (a) a shape of one or more of the elongated structures and (b) the elongated structure surface are chosen such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface.

With such structures it may be possible to create a relatively even outcoupling of the light source light from the structure when such light source light is coupled into the structure (at the first structure part). If desired, also an uneven outcoupling of the light source is possible. Hence, with such structure the outcoupling over the length of the structure may better be controlled, which may amongst others be due to the use of 3D printing. The surface may e.g. comprise outcoupling structures or outcoupling branched, or outcoupling bends, etc... Hence, with the present invention it may be possible to provide e.g. a thin downlight with an essentially homogeneous light emission (from e.g. a planar downlight) using FDM printed light guides. Hence, the structured may be used as light guides.

As indicated above, a method for producing a 3D item by means of fused deposition modelling comprises a 3D printing stage comprising layer-wise depositing an extrudate comprising 3D printable material, to provide the 3D item comprising 3D printed material, wherein the 3D item comprises one or more layers (especially a plurality of layers) of 3D printed material. This 3D printing method or process is further also elucidated below. Basically, 3D printable material is deposited, and thereby a 3D printed item comprising 3D printed material is obtained.

Especially, the method comprises providing during the 3D printing stage one or more, especially a plurality of 3D printed elongated structures. One or more of the 3D printed elongated structures, especially all comprise 3D printed material, a first structure part, a second structure part, and an elongated structure surface between the first structure part and the second structure part. Hence, with 3D printing of 3D printable material, and elongated structure may be created having a first structure part and a second structure part.

The first structure part may be a first end of the 3D printed elongated structure. The second structure part may be a second end of the 3D printed elongated structure. The first structure part may be a first end of the 3D printed elongated structure and the second structure part may be a second end of the 3D printed elongated structure. Two (or more) first structure parts may be connected via a 3D printed connecting part. Alternatively, or additionally, two (or more) second structure parts may be connected via a(nother) 3D printed connecting part. For instance, the result of 3D continuous printing may be that two second structure parts may be essentially be the same part of a 3D printed structure or combination of 3D printed structures. Hence, first structure parts and second structure parts may be connected when continuous printing is used.

Especially, the first structure part may be used to couple light source light into the 3D printed elongated structure. Hence, the first structure part may also be indicated as light entrance point. Hence, the first structure parts may be parts that are (especially) suitable for incoupling of light source light, especially for subsequent propagation through the elongated structure (in the direction of the second structure part).

Note that the first structure part or the second structure part are thus not necessarily ends of a 3D printed structure. They may be ends, but one or more of the first structure part or the second structure part may also not be ends as 3D printed structure may be connected. As indicated above, in continuous 3D printing, e.g. the second structure ends may essentially be connected as it may be a continuous structure.

In general, the effective length (or effective distance) between the first structure part and the second structure part are (defined) as at least 1 cm. Hence, an elongated 3D printed part having a length of at least 1 cm may be a 3D printed elongated structure. In general, the effective length may be at least 2 cm, such as at least 5 cm, like at least 10 cm. Hence, an elongated 3D printed part having a length of at least 2 cm may be a 3D printed elongated structure. In disc-like structures, the effective length may be at least 50%, such as at least 70%, like at least 80% of the radius.

A length along a body axis or axis of elongation may be longer than the effective length, when the 3D printed elongated structure includes one or more bends. A first length (LI) between the first structure part and the second structure part measured along an axis of elongation (A) of the 3D printed elongated structure may be at least 1 cm. Hence, an elongated 3D printed part having a first length of at least 1 cm may be a 3D printed elongated structure. Especially, the first length may be at least 2 cm, such as at least 2 cm.

In examples, such as continuously 3D printed structures, the first structure end and/or the second structure end may be cross-sections (perpendicular to an axis of elongation of the 3D printed elongated structure. The structure surface may then be the surface of the 3D printed elongated structure between these cross-sections.

Hence, it may especially be desirable that the light source light may propagate along the first length, such that over an essential part of the first length, light source light may be coupled out via the structure surface. The first structure part and the second structure part may essentially define the structure, such as e.g. the (effective) length of the structure (see also below). The surface of the structure between the first structure part and the second structure part is indicated as elongated structure surface. The structure may have a length, measure along the shape of the structure. Further, the structure may have a width and height, or a diameter. As the structure is elongated, the length is especially larger than the width and height, or especially larger than the diameter, as known to a person skilled in the art.

For instance, the length may be at least about 2 times, such as at least about 5 time, like at least about 10 times, such as even more especially at least about 30 times the width or height or diameter. The effective length, i.e. the length between the first structure part and the second structure part not considering curvatures (should they be available), may be shorter than the length. However, in general it may apply that also the effective length may be at least about 2 times, such as at least about 5 time, like at least about 10 times the width or height or diameter.

Especially, the 3D printable material is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation. Hence, also the deposited 3D printable material, i.e. the 3D printed material is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation. The 3D printed material (and thus the 3D printable material may at least be transmissive for visible light, such as white light. The terms“visible”,“visible light” or“visible emission” and similar terms refer to light having one or more wavelengths in the range of about 380- 780 nm. The term“white light” herein, is known to the person skilled in the art. It especially relates to light having a correlated color temperature (CCT) between about 1800 K and 20000 K, such as between 2000 and 20000 K, especially 2700-20000 K, for general lighting especially in the range of about 2700 K and 6500 K. For backlighting purposes the correlated color temperature (CCT) may especially be in the range of about 7000 K and 20000 K. The correlated color temperature (CCT) may be within about 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about 10 SDCM from the BBL, even more especially within about 5 SDCM from the BBL.

The light transmissive material has light guiding or wave guiding properties. Hence, the light transmissive material is herein also indicated as waveguide material or light guide material. The light transmissive material will in general have (some) transmission of one or more of (N)UV, visible and (N)IR radiation. The transmission of the light transmissive material for one or more of (N)UV, visible and (N)IR radiation may be at least 80%/cm, such as at least 90%/cm, even more especially at least 95%/cm, such as at least 98%/cm, such as at least 99%/cm.

Herein, values for transmission especially refer to transmission without taking into account Fresnel losses at interfaces (with e.g. air). Hence, the term“transmission” especially refers to the internal transmission. By transmission we refer to the intrinsic transmission values of the polymer used. For example when an extruded rod with a length of 30 cm and diameter of 1 cm having a smooth surface is produced using the polymer for printing without additives intensity of light entering from one side I(in) and the intensity of light exiting the opposite surface I(exit) is preferably 0.8< I(exit)/I(in). Furthermore, this ratio preferably does not show a wavelength dependence. Thus, losses (scattering and absorption) do not show wavelength dependence.

Hence, the composition of the 3D printable material (and thus 3D printed material) and the dimensions of structures may be chosen such that a light transmissive structure is provided, especially a light transmissive structure which, when light source light is coupled into the structure at e.g. the first structure part, at least part of the light source light, also exits from the second structure part. However, when outcoupling of the light source light over at least part of the length of the structure is desired, the shape and or properties (such as transmission, light scattering) of the 3D printed material, may be chosen such, that at least part of the light source light is coupled out of the structure when propagating from the first structure part in the direction of the second structure part. For instance, total internal reflection may be decreased by providing structures with one or more curvatures (“bends”). Alternatively, or additionally, structures may be provided with scattering elements in the 3D printed material (and thus also in the 3D printable material).

Yet alternatively or additionally, structures may be provided with scattering elements at the surface of the structures.

Therefore, especially one or more of (a) a shape of one or more of the elongated structures and (b) the elongated structure surface are chosen such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface.

The 3D printed elongated structure may be chosen such that light source light that propagates from the first structure part to the second structure part reaches the second structure part. Only a small part may reach the second structure part. For instance, less than 10% of the total power of the light source light (at the first structure part) may reach the second structure part (and thus travel over a distance of at least 1 cm, or at least 2 cm, like at least 5 cm).

A ratio between the amount of light reaching the second structure part and the amount of light escaping via the surface may depend on the desired properties of e.g. the lighting device. However, at least 1% of the total power that is introduced at the first structure part into the structure may leave the structure via the surface and at maximum 5% of the total power that is introduced at the first structure part into the structure may leave the structure via the second structure part. At least 10% of the total power that is introduced at the first structure part into the structure may leave the structure via the surface, such as at least 20%, like at least 50%.

The 3D printed elongated structures may be selected (like material, length, width/height or diameter) such that a second part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure at the second structure part, wherein an intensity ratio (Watt/Watt) of the second part to the first part is equal to or smaller than 0.1. The indication“Watt/W att” indicates the ratio of powers of the light source light in Watts.

The 3D printed elongated structures may be selected (like material, length, width/height or diameter) such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface, wherein an intensity ratio (Wi/Wo) of the first part to the initial power of the light source light at the first structure part is

O. KWi/Wo <1, like 0.5<Wi/Wo <1, such as 0.8<Wi/Wo <0.99. Especially, the first length between the first structure part and the second structure part is at least 2 cm.

The 3D printed elongated structures may be selected (like material, length, width/height or diameter) such that a second part of the radiation propagating through the elongated structure from the first structure part to the second structure part reaches the second structure part, wherein an intensity ratio (Watt/Watt) of the second part to the first part is equal to or smaller than 0.1.

Hence, at maximum 10% of the initial power at the first structure part may reach the second structure part, such as at maximum.

Hence, the intensity in Watt of the light source light in the 3D printed elongated structure reduces with distance from the first structure part due to outcoupling from the 3D printed elongated structure (to the external thereol) via the elongated structure surface. The 3D printed elongated structures may be selected (like material, length, width/height or diameter) such that the outcoupling is essentially even over the elongated structure length (or first length).

As indicated above, when an elongated structure is essentially straight, due to total internal reflection essentially no light may escape from the elongated structure via the surface. This may however be different when the structure includes curves. The, not all light may be totally internally reflected, and light may escape from the structure at the curves.

One or more of the 3D printed elongated structures have a structure height (HI), and the method further comprises printing the one or more 3D printed elongated structures with one or more curvatures (B) in a plane (P) (parallel to the effective structure length (LI) and) perpendicular to the structure height (HI). Therefore, the structures may e.g. form a planar element, like a disc-like element, wherein in the plane of the element the structures have curves.

One or more of the 3D printed elongated structures have a structure width (Wl), and the method comprises printing the one or more 3D printed elongated structures with (i) radii (r) of the one or more curvatures (B) and (ii) the structure width (Wl) chosen such that the first part of the radiation escapes from the (one or more) elongated structures via the elongated structure surfaces at one or more of the curvatures (B).

The radii (r) and the structure width (Wl) may have a ratio selected from the range of 0.2<r/Wl<50, especially a ratio selected from the range of 0.5<r/Wl<20.

For radially arranged structures, such as an element have a disc-like shape defined by at least a plurality of structures, from the edge to the center less and less space is available for the structures. In order to cope with this effect, one may use structure with different lengths, or structures that are branched (with more and/or larger branched closer to the edge than to the center). Alternatively, or additionally, one may use structures that are curved, wherein the curvatures define a decreasing effective width with distance from the edge. Hence, the method may comprise printing the one or more 3D printed elongated structures with radii (r) which decrease with increasing distance from the curvatures (B) from the first structure part.

The curved structure may have a kind of meandering shape. The curved structures may have a plane of symmetry which may also include the effective length axis.

As indicated above, alternative or additional to e.g. curvatures, it may also be possible to provide the surface of the structures with outcoupling properties. Such outcoupling structures may be provided after having printed the 3D item. Such outcoupling structures may alternatively or additionally also be provided during printing (i.e. during the printing stage). For instance, a core-shell printing strategy may be chosen wherein the shell comprises outcoupling structures, like particles, such as (light reflective) flakes and/or high refractive particles such as titanium oxide, and the core essentially has no such particles or to a lower extend (like volume % at least 10 times lower than in the shell). It may be possible to bring defects into the side surface of the of the light guiding structure by adjusting the flow (stop and start printing again) of the polymer during printing.

After deposition surface irregularities may be created, e.g. with a relatively sharp item. In this way, e.g. scratches may be introduced, which may facilitate light outcoupling.

Alternatively, or additionally, the structures may be elongated and may have one or more branches. Such branches may have dimensions like (effective) length, width and height, or diameter, of which one or more may be identical to the main part of the structure, and/or of which one or more may be smaller than of the main part of the structure. In general, at least the latter applies.

Alternatively, or additionally, the height of the structure(s) may vary over the (effective) length of the structure(s). This may also have effect on the total internal reflection an facilitate outcoupling. For instance, a disc-like shape may have an increasing height with increasing distance from a central point.

Hence, the method may comprise one or more of: (i) printing one or more 3D printed elongated structures with elongated structure surfaces comprising radiation outcoupling structures for facilitating outcoupling of radiation from the one or more elongated structure via the elongated structure surfaces, and (ii) printing one or more 3D printed elongated structures with one or more 3D printed structure branches, branching away from the 3D printed elongated structure. Alternatively, or additionally, the method may comprise (iii) printing one or more 3D printed elongated structures with one or more shape irregularities by reducing a flow of the 3D printable material during printing. The term “shape irregularity” may refer to a defect. Such irregularity may e.g. be created by reducing the flow of 3D printable material, or even temporarily stopping the flow of 3D printable material, during printing of a layer.

The structures are especially printed along their length axis or axis of elongation. Hence, the width of the structure may essentially be the width of a 3D printed layer. Hence, when 3D printing the 3D printable material of the structure, the printing direction may follow the shape of the structure. Therefore, the printing direction when 3D printing the structure may be along the (predefined axis of elongation of the structure (being printed). Hence, a printing direction (during printing of the elongated structure) may be parallel to an axis of elongation of a respective 3D printed structure.

As indicated above, the method may comprise printing the elongated structures in a radial configuration. In this way, e.g. a disc of structures may be created or a disc comprising a plurality of structures. Such radial configuration may comprise at least four, such as at least six, like at least eight, like at least 12 structures that are radially configured. Another configuration than radial may also be possible, like parallel

configuration in a square or rectangular (but non-square) configuration. Especially, the configuration herein may be relatively planar configuration, such as essentially not higher than the height of the structures.

As indicated above, the method comprises depositing during a printing stage 3D printable material. Herein, the term“3D printable material” refers to the material to be deposited or printed, and the term“3D printed material” refers to the material that is obtained after deposition. These materials may be essentially the same, as the 3D printable material may especially refer to the material in a printer head or extruder at elevated temperature and the 3D printed material refers to the same material, but in a later stage when deposited. The 3D printable material is printed as a filament and deposited as such. The 3D printable material may be provided as filament or may be formed into a filament. Hence, whatever starting materials are applied, a filament comprising 3D printable material is provided by the printer head and 3D printed. The term“extrudate” may be used to define the 3D printable material downstream of the printer head, but not yet deposited. The latter is indicated as“3D printed material”. In fact, the extrudate comprises 3D printable material, as the material is not yet deposited. Upon deposition of the 3D printable material or extrudate, the material is thus indicated as 3D printed material. Essentially, the materials are the same material, as the thermoplastic material upstream of the printer head, downstream of the printer head, and when deposited, is essentially the same material.

Herein, the term“3D printable material” may also be indicated as“printable material. The term“polymeric material” may refer to a blend of different polymers but may also refer to essentially a single polymer type with different polymer chain lengths. Hence, the terms“polymeric material” or“polymer” may refer to a single type of polymers but may also refer to a plurality of different polymers. The term“printable material” may refer to a single type of printable material but may also refer to a plurality of different printable materials. The term“printed material” may refer to a single type of printed material but may also refer to a plurality of different printed materials.

Hence, the term“3D printable material” may also refer to a combination of two or more materials. In general, these (polymeric) materials have a glass transition temperature T_g and/or a melting temperature T_m. The 3D printable material will be heated by the 3D printer before it leaves the nozzle to a temperature of at least the glass transition temperature, and in general at least the melting temperature. Hence, the 3D printable material may comprise a thermoplastic polymer having a glass transition temperature (T_g) and /or a melting point (T_m), and the printer head action comprises heating the 3D printable material above the glass transition and if it is a semi-crystalline polymer above the melting temperature. The 3D printable material may comprise a (thermoplastic) polymer having a melting point (T_m), and the printer head action comprises heating the 3D printable material to be deposited on the receiver item to a temperature of at least the melting point. The glass transition temperature is in general not the same thing as the melting temperature. Melting is a transition which occurs in crystalline polymers. Melting happens when the polymer chains fall out of their crystal structures and become a disordered liquid. The glass transition is a transition which happens to amorphous polymers; that is, polymers whose chains are not arranged in ordered crystals, but are just strewn around in any fashion, even though they are in the solid state. Polymers can be amorphous, essentially having a glass transition temperature and not a melting temperature or can be (semi) crystalline, in general having both a glass transition temperature and a melting temperature, with in general the latter being larger than the former. The glass temperature may e.g. be determined with differential scanning calorimetry. The melting point or melting temperature can also be determined with differential scanning calorimetry.

The method described above comprises providing a filament of 3D printable material and printing during a printing stage said 3D printable material on a substrate, to provide said 3D item.

Materials that may especially qualify as 3D printable materials may be selected from the group consisting of metals, glasses, thermoplastic polymers, silicones, etc. Especially, the 3D printable material comprises a (thermoplastic) polymer selected from the group consisting of ABS (acrylonitrile butadiene styrene), Nylon (or polyamide), Acetate (or cellulose), PLA (poly lactic acid), terephthalate (such as PET polyethylene terephthalate), Acrylic (polymethylacrylate, Perspex, polymethylmethacrylate, PMMA), Polypropylene (or polypropene), Polycarbonate (PC), Polystyrene (PS), PE (such as expanded- high impact- Polythene (or polyethene), Low density (LDPE) High density (HDPE)), PVC (polyvinyl chloride) Polychloroethene, such as thermoplastic elastomer based on copolyester elastomers, polyurethane elastomers, polyamide elastomers polyolefine based elastomers, styrene based elastomers, etc.. Optionally, the 3D printable material comprises a 3D printable material selected from the group consisting of Urea formaldehyde, Polyester resin, Epoxy resin, Melamine formaldehyde, thermoplastic elastomer, etc... Optionally, the 3D printable material comprises a 3D printable material selected from the group consisting of a polysulfone.

Elastomers, especially thermoplastic elastomers, are especially interesting as they are flexible and may help obtaining relatively more flexible filaments comprising the thermally conductive material. A thermoplastic elastomer may comprise one or more of styrenic block copolymers (TPS (TPE-s)), thermoplastic polyolefin elastomers (TPO (TPE-o)),

thermoplastic vulcanizates (TPV (TPE-v or TPV)), thermoplastic polyurethanes (TPU (TPU)), thermoplastic copolyesters (TPC (TPE-E)), and thermoplastic polyamides (TPA (TPE-A)).

Suitable thermoplastic materials, such as also mentioned in WO2017/040893, may include one or more of polyacetals (e.g., polyoxyethylene and poly oxy methylene), poly(Ci-₆ alkyl)acrylates, polyacrylamides, polyamides, (e.g., aliphatic polyamides, polyphthalamides, and polyaramides), polyamideimides, polyanhydrides, polyarylates, polyarylene ethers (e.g., polyphenylene ethers), polyarylene sulfides (e.g., polyphenylene sulfides), polyarylsulfones (e.g., polyphenylene sulfones), polybenzothiazoles,

polybenzoxazoles, polycarbonates (including polycarbonate copolymers such as

polycarbonate-siloxanes, polycarbonate-esters, and polycarbonate-ester-siloxanes), polyesters (e.g., polycarbonates, polyethylene terephthalates, polyethylene naphtholates, poly butylene terephthalates, polyarylates), and polyester copolymers such as polyester-ethers),

polyetheretherketones, polyetherimides (including copolymers such as polyetherimide- siloxane copolymers), polyetherketoneketones, polyetherketones, polyethersulfones, polyimides (including copolymers such as polyimide- siloxane copolymers), poly(Ci-₆ alkyl)methacrylates, polymethacrylamides, polynorbomenes (including copolymers containing norbomenyl units), polyolefins (e.g., polyethylenes, polypropylenes,

polytetrafluoroethylenes, and their copolymers, for example ethylene- alpha- olefin copolymers), polyoxadiazoles, polyoxymethylenes, polyphthalides, polysilazanes, polysiloxanes, polystyrenes (including copolymers such as acrylonitrile-butadiene-styrene (ABS) and methyl methacrylate-butadiene-styrene (MBS)), polysulfides, polysulfonamides, polysulfonates, polysulfones, polythioesters, polytriazines, polyureas, polyurethanes, polyvinyl alcohols, polyvinyl esters, polyvinyl ethers, polyvinyl halides, polyvinyl ketones, polyvinyl thioethers, polyvinylidene fluorides, or the like, or a combination comprising at least one of the foregoing thermoplastic polymers. Examples of polyamides may include, but are not limited to, synthetic linear polyamides, e.g., Nylon-6,6; Nylon-6,9; Nylon-6,10;

Nylon-6,12; Nylon-11; Nylon-12 and Nylon-4,6, preferably Nylon 6 and Nylon 6,6, or a combination comprising at least one of the foregoing. Polyurethanes that can be used include aliphatic, cycloaliphatic, aromatic, and polycyclic polyurethanes, including those described above. Also useful are poly(Ci-6 alkyl)acrylates and poly(Ci-6 alkyl)methacrylates, which include, for instance, polymers of methyl acrylate, ethyl acrylate, acrylamide, methacrylic acid, methyl methacrylate, n-butyl acrylate, and ethyl acrylate, etc. A polyolefine may include one or more of polyethylene, polypropylene, polybutylene, polymethylpentene (and co-polymers thereof), polynorbomene (and co-polymers thereof), poly f -butene, poly (3 - methylbutene), poly(4-methylpentene) and copolymers of ethylene with propylene, f -butene, f -hexene, f-octene, f-decene, 4-methyl-l-pentene and f - octadecene.

The 3D printable material (and the 3D printed material) may comprise one or more of polycarbonate (PC), styrene-acrylonitrile resin (SAN), amorphous polytethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), poly (methyl methacrylate) (PMMA), polystyrene (PS), polyurethane (PU), polysiloxane, and styrene acrylic copolymers (SMMA), and low crystalline transparent polypropylene and (low crystalline transparent) polyethylene.

The 3D printed elongated structure may (also) comprise one or more layers of 3D printed material. Such layers may be on top of each other and/or next to each other.

The term 3D printable material is further also elucidated below, but especially refers to a thermoplastic material, optionally including additives, to a volume percentage of at maximum about 60%, especially at maximum about 30 vol.%, such as at maximum 20 vol.% (of the additives relative to the total volume of the thermoplastic material and additives).

The printable material may comprise two phases. The printable material may comprise a phase of printable polymeric material, especially thermoplastic material (see also below), which phase is especially an essentially continuous phase fn this continuous phase of thermoplastic material polymer additives such as one or more of antioxidant, heat stabilizer, light stabilizer, ultraviolet light stabilizer, ultraviolet light absorbing additive, near infrared light absorbing additive, infrared light absorbing additive, plasticizer, lubricant, release agent, antistatic agent, anti-fog agent, antimicrobial agent, colorant, laser marking additive, surface effect additive, radiation stabilizer, flame retardant, anti-drip agent may be present. The additive may have useful properties selected from optical properties, mechanical properties, electrical properties, thermal properties, and mechanical properties (see also above).

The printable material may comprise particulate material, i.e. particles embedded in the printable polymeric material, which particles form a substantially discontinuous phase. The number of particles in the total mixture is especially not larger than 60 vol.%, relative to the total volume of the printable material (including the (anisotropically conductive) particles) especially in applications for reducing thermal expansion coefficient. For optical and surface related effect number of particles in the total mixture is equal to or less than 20 vol.%, such as up to 10 vol.%, relative to the total volume of the printable material (including the particles). Hence, the 3D printable material especially refers to a continuous phase of essentially thermoplastic material, wherein other materials, such as particles, may be embedded. Likewise, the 3D printed material especially refers to a continuous phase of essentially thermoplastic material, wherein other materials, such as particles, are embedded. The particles may comprise one or more additives as defined above. Hence, the 3D printable materials may comprise particulate additives.

The printable material is printed on a receiver item. Especially, the receiver item can be the building platform or can be comprised by the building platform. The receiver item can also be heated during 3D printing. However, the receiver item may also be cooled during 3D printing.

The phrase“printing on a receiver item” and similar phrases include amongst others directly printing on the receiver item, or printing on a coating on the receiver item, or printing on 3D printed material earlier printed on the receiver item. The term“receiver item” may refer to a printing platform, a print bed, a substrate, a support, a build plate, or a building platform, etc... Instead of the term“receiver item” also the term“substrate” may be used. The phrase“printing on a receiver item” and similar phrases include amongst others also printing on a separate substrate on or comprised by a printing platform, a print bed, a support, a build plate, or a building platform, etc... Therefore, the phrase“printing on a substrate” and similar phrases include amongst others directly printing on the substrate, or printing on a coating on the substrate or printing on 3D printed material earlier printed on the substrate. Here below, further the term substrate is used, which may refer to a printing platform, a print bed, a substrate, a support, a build plate, or a building platform, etc., or a separate substrate thereon or comprised thereby.

Layer by layer printable material is deposited, by which the 3D printed item is generated (during the printing stage). The 3D printed item may show a characteristic ribbed structure (originating from the deposited filaments). However, it may also be possible that after a printing stage, a further stage is executed, such as a finalization stage. This stage may include removing the printed item from the receiver item and/or one or more post processing actions. One or more post processing actions may be executed before removing the printed item from the receiver item and/or one more post processing action may be executed after removing the printed item from the receiver item. Post processing may include e.g. one or more of polishing, coating, adding a functional component, etc... Post-processing may include smoothening the ribbed structures, which may lead to an essentially smooth surface.

A software product can be used to execute the method described herein. A computer program product, when running on a computer which is functionally coupled to or comprised by a fused deposition modeling 3D printer, may be capable of bringing about the method as described herein.

The herein described method provides 3D printed items. A 3D printed item obtainable with the herein described method comprises 3D printed material, wherein the 3D item comprises one or more layers (especially a plurality of layers) of 3D printed material, wherein the 3D item comprises one or more, especially a plurality of, 3D printed elongated structures, each comprising 3D printed material, a first structure part, a second structure part, and an elongated structure surface between the first structure part and the second structure part, wherein the 3D printed material of one or more of the structures, especially of all, is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation. Further, especially one or more of (a) a shape of one or more of the (one or more) elongated structures and (b) the elongated structure surface of one or more of the (one or more) elongated structures are chosen such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface. The 3D item may comprises 3D printed material, wherein the 3D item comprises one or more layers (especially a plurality of layers) of 3D printed material, wherein the 3D item comprises a plurality of 3D printed elongated structures, each comprising 3D printed material, a first structure part, a second structure part, and an elongated structure surface between the first structure part and the second structure part, wherein the 3D printed material is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein one or more of (a) a shape of one or more of the elongated structures and (b) the elongated structure surface of one or more of the elongated structures are chosen such that a first part of the radiation propagating through the elongated structure from the first structure part to the second structure part escapes from the elongated structure via the elongated structure surface.

The 3D printed item may comprise a plurality of layers on top of each other, i.e. stacked layers. The thickness and height of the layers may be selected from the range of 100 - 3000 pm, such as 200-2500 pm, with the height in general being smaller than the width. For instance, the ratio of height and width may be equal to or smaller than 0.8, such as equal to or smaller than 0 6

Layers may be core-shell layers or may consist of a single material. Within a layer, there may also be a change in composition, for instance when a core-shell printing process was applied and during the printing process it was changed from printing a first material (and not printing a second material) to printing a second material (and not printing the first material). During printing thickness of the core and the shell layer may be altered for enabling light outcoupling. Instead of total core shell the layers may have sandwich structure where the inner layer and outer layer are continuous.

At least part of the 3D printed item may include a coating.

As indicated above, one or more of the 3D printed elongated structures may have a structure height (HI) (and an effective structure length (LI)). The one or more of the 3D printed elongated structures may comprise curvatures (B) in a plane (P) (parallel to the effective structure length (LI) and) perpendicular to the structure height (HI), wherein the 3D printed elongated structures have a structure width (Wl). Further, especially one or more of the curvatures (B) have radii (r), wherein (i) the radii (r) and (ii) the structure width (Wl) are chosen such that the first part of the radiation escapes from the (one or more) elongated structures via the elongated structure surfaces at one or more of the curvatures (B).

Two or more of the elongated structure may be mutually connected via bridges. Such bridges may also be 3D printed. Especially, the bridges may be closer to the first structure part than to the second structure part in radially configured elongated structures (wherein the first structure parts are configured at a larger radius than the second structure parts).

As indicated above, the radii (r) of one or more 3D printed elongated structures may decrease with increasing distance from the curvatures (B) from the first structure part.

Yet further, one or more of the following may apply: (i) the elongated structure surface of one or more 3D printed elongated structures comprise radiation outcoupling structures for facilitating outcoupling of radiation from the one or more elongated structures via the elongated structure surface, and (ii) one or more 3D printed elongated structures comprise one or more 3D printed structure branches, branching away from the 3D printed elongated structure. Alternatively, or additionally, (iii) one or more 3D printed elongated structures may comprise shape irregularities (see also above). Yet further, alternatively or additionally, (iv) one or more 3D printed elongated structures comprise a layer have a core-shell structure, wherein the core is transmissive for radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein the shell has a variable shell thickness for facilitating light outcoupling from the core out of the layer via a shell part having a reduced shell thickness. For instance, at some parts of the shell, the shell may be interrupted (i.e. having no (i.e. zero) shell thickness). The core may comprise the transparent material, and the shell material may be different or have other optical properties, such as light scattering. During printing thickness of core and shell may change to enable light outcoupling (in the 3D printed product (which is being printed)).

As indicated above, the elongated structures may be configured in a radial configuration. Hence, a disc shaped element may be provided comprising a plurality of radially configured elongated elements.

The (with the herein described method) obtained 3D printed item may be functional per se. For instance, the 3D printed item may be a lens, a collimator, a reflector, or a light guide. The thus obtained 3D item may (alternatively) be used for decorative or artistic purposes. The 3D printed item may include or be provided with a functional component. The functional component may especially be selected from the group consisting of an optical component, an electrical component, and a magnetic component. The term“optical component” especially refers to a component having an optical functionality, such as a lens, a mirror, a light transmissive element, an optical filter, and a light guide. The term optical component may also refer to a light source (like a LED). The term“electrical component” may e.g. refer to an integrated circuit, PCB, a battery, a driver, but also a light source (as a light source may be considered an optical component and an electrical component), etc. The term magnetic component may e.g. refer to a magnetic connector, a coil, etc... Alternatively, or additionally, the functional component may comprise a thermal component (e.g.

configured to cool or to heat an electrical component). Hence, the functional component may be configured to generate heat or to scavenge heat, etc... As indicated above, the 3D printed item maybe used for different purposes. Amongst others, the 3D printed item maybe used in lighting. Hence, a lighting system may comprise (a) a light source configured to provide (visible) light source light and (b) the 3D item as defined herein, wherein 3D item may be configured as one or more of (i) at least part of a housing, (ii) at least part of a wall of a lighting chamber, and (iii) a functional component, wherein the functional component may be selected from the group consisting of an optical component (such as a light guide), a support, an electrically insulating component, an electrically conductive component, a thermally insulating component, and a thermally conductive component. Hence, the 3D item may be configured as one or more of (i) at least part of a lighting device housing, (ii) at least part of a wall of a lighting chamber, and (iii) an optical element, such as a light guide. As a relative smooth surface may be provided, the 3D printed item may be used as mirror or lens, etc... The 3D item may be configured as shade. A device or system may comprise a plurality of different 3D printed items, having different functionalities.

Especially, however, the structures may be used as light guides. Hence, the 3D item may have light guiding properties, and may especially be combined with one or more especially a plurality of light sources. For instance, each first structure part may be configured in a light receiving relationship with one or more light sources, especially solid- state light sources.

The term“light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc... The term“light source” may also refer to an organic light-emitting diode, such as a passive-matrix (P MOLED) or an active-matrix (AMOLED). The light source may comprise a solid-state light source (such as a LED or laser diode). The light source may comprise a LED (light emitting diode). The term LED may also refer to a plurality of LEDs. Further, the term“light source” may also refer to a so-called chips-on-board (COB) light source. The term“COB” especially refers to LED chips in the form of a semiconductor chip that is neither encased nor connected but directly mounted onto a substrate, such as a PCB. Hence, a plurality of semiconductor light sources may be configured on the same substrate. A COB may be a multi LED chip configured together as a single lighting module. The term“light source” may also relate to a plurality of (essentially identical (or different)) light sources, such as 2-2000 solid state light sources. The light source may comprise one or more micro-optical elements (array of micro lenses) downstream of a single solid-state light source, such as a LED, or downstream of a plurality of solid state light sources (i.e. e.g. shared by multiple LEDs). The light source may comprise a LED with on-chip optics. The light source may comprise a pixelated single LEDs (with or without optics), which may offer on-chip beam steering.

The phrases“different light sources” or“a plurality of different light sources”, and similar phrases, may refer to a plurality of solid-state light sources selected from at least two different bins. Likewise, the phrases“identical light sources” or“a plurality of same light sources”, and similar phrases, may refer to a plurality of solid-state light sources selected from the same bin.

A lighting device may comprise the 3D item as defined herein, and a plurality of light sources configured to generate radiation having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein the plurality of 3D printed elongated structures are configured in a light receiving relationship with the plurality of light sources such that at least part of the radiation propagates in a direction from the first structure part to the second structure part.

Hence, the light source and the structure may be radiationally coupled (in the lighting device). The terms "radiationally coupled" or“optically coupled” may especially mean that (i) a light generating element, such as a light source, and (ii) another item or material, are associated with each other so that at least part of the radiation emitted by the light generating element is received by the item or material. In other words, the item or material is configured in a light-receiving relationship with the light generating element. At least part of the radiation of the light generating element will be received by the item or material. This may be directly, such as the item or material in physical contact with the (light emitting surface of the) light generating element. This may be via a medium, like air, a gas, or a liquid or solid light guiding material. One or more optics, like a lens, a reflector, an optical filter, may be configured in the optical path between light generating element and item or material.

The lighting device may comprise a plate-like shape. Especially, the first structure parts may define an edge face, wherein the light sources are configured upstream of the edge face.

Hence, the light sources may be configured in a circle surrounding the first structure parts of the 3D printed elongated structures.

Further, the lighting device may further comprise a reflector and a radiation transmissive diffusor, wherein the plurality of 3D printed elongated structures are configured between the reflector and the diffusor, wherein the reflector is configured to reflect at least part of the radiation that has escaped from one or more of the 3D printed elongated structures in a direction of the diffusor. In this way, a relatively flat lighting device may be created. Light source light may escape from the structures via outcoupling elements and/or curves (as in fact outcoupling elements) and/or branches (as in fact outcoupling elements).

Relevant 3D printed materials are described above. Further, as also indicated above, the elongated structures may be configured in a radial configuration, though other configurations may also be possible. As indicated above, the 3D printed material may comprise one or more of polycarbonate (PC), styrene-acrylonitrile resin (SAN), amorphous polytethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), poly(methyl methacrylate) (PMMA), polystyrene (PS), polyurethane (PU), polysiloxane, and styrene acrylic copolymers (SMMA), and low crystalline transparent polypropylene and

polyethylene.

Further, as also elucidated above, the elongated structures may be configured in a radial configuration. For instance, an effective length, defined as a (shortest) length between the first structure part and the second structure part may be at least 50% of the radius. Likewise, the first length between the first structure part and the second structure part may also be at least 50% of the radius, or even at least 100% in case bends are available.

Returning to the 3D printing process, a specific 3D printer may be used to provide the 3D printed item described herein. A fused deposition modeling 3D printer comprises (a) a printer head comprising a printer nozzle, and (b) a 3D printable material providing device configured to provide 3D printable material to the printer head, wherein the fused deposition modeling 3D printer is configured to provide said 3D printable material according to the herein described method. The printer nozzle may include a single opening. The printer nozzle may be of the core-shell type, having two (or more) openings. The term “printer head” may also refer to a plurality of (different) printer heads; hence, the term “printer nozzle” may also refer to a plurality of (different) printer nozzles.

The 3D printable material providing device may provide a filament comprising 3D printable material to the printer head or may provide the 3D printable material as such, with the printer head creating the filament comprising 3D printable material. Hence, a fused deposition modeling 3D printer may comprise (a) a printer head comprising a printer nozzle, and (b) a filament providing device configured to provide a filament comprising 3D printable material to the printer head, wherein the fused deposition modeling 3D printer is configured to provide said 3D printable material to a substrate, such as according to the herein described method. Especially, the 3D printer comprises a controller (or is functionally coupled to a controller) that is configured to execute in a controlling mode (or“operation mode”) the method as described herein.

The system, or apparatus, or device may execute an action in a“mode” or “operation mode” or“mode of operation”. Likewise, in a method an action or stage, or step may be executed in a“mode” or“operation mode” or“mode of operation”. The term“mode” may also be indicated as“controlling mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and/or after executing the mode one or more other modes may be executed.

A control system may be available, that is adapted to provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operation mode may also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e.“on”, without further tunability).

Instead of the term“fused deposition modeling (FDM) 3D printer” shortly the terms“3D printer”,“FDM printer” or“printer” may be used. The printer nozzle may also be indicated as“nozzle” or sometimes as“extruder nozzle”.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figs la-lc schematically depict some general aspects of the 3D printer and of a of 3D printed material;

Figs. 2a-2g schematically depict some aspects of the structure;

Figs. 3a-3c schematically depict a lighting device 1000; and

Figs. 4a-4f schematically depict some further variants.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. la schematically depicts some aspects of the 3D printer. Reference 500 indicates a 3D printer. Reference 530 indicates the functional unit configured to 3D print, especially FDM 3D printing; this reference may also indicate the 3D printing stage unit.

Here, only the printer head for providing 3D printed material, such as an FDM 3D printer head is schematically depicted. Reference 501 indicates the printer head. The 3D printer of the present invention may especially include a plurality of printer heads (see below).

Reference 502 indicates a printer nozzle. The 3D printer of the present invention may especially include a plurality of printer nozzles, though other embodiments are also possible. Reference 320 indicates a filament of printable 3D printable material (such as indicated above). For the sake of clarity, not all features of the 3D printer have been depicted, only those that are of especial relevance for the present invention (see further also below).

Reference 321 indicates extrudate (of 3D printable material 201).

The 3D printer 500 is configured to generate a 3D item 1 by layer-wise depositing on a receiver item 550, which may at least temporarily be cooled, a plurality of layers 322 wherein each layers 322 comprises 3D printable material 201, such as having a melting point T_m. The 3D printable material 201 may be deposited on a substrate 1550 (during the printing stage). By deposition, the 3D printable material 201 has become 3D printed material 202. 3D printable material 201 escaping from the nozzle 502 is also indicated as extrudate 321.

The 3D printer 500 may be configured to heat the filament 320 material upstream of the printer nozzle 502. This may e.g. be done with a device comprising one or more of an extrusion and/or heating function. Such device is indicated with reference 573 and is arranged upstream from the printer nozzle 502 (i.e. in time before the filament material leaves the printer nozzle 502). The printer head 501 may (thus) include a liquefier or heater. Reference 201 indicates printable material. When deposited, this material is indicated as (3D) printed material, which is indicated with reference 202.

Reference 572 indicates a spool or roller with material, especially in the form of a wire, which may be indicated as filament 320. The 3D printer 500 transforms this in an extrudate 321 downstream of the printer nozzle which becomes a layer 322 on the receiver item or on already deposited printed material. In general, the diameter of the extrudate 321 downstream of the nozzle 502 is reduced relative to the diameter of the filament 322 upstream of the printer head 501. Hence, the printer nozzle is sometimes (also) indicated as extruder nozzle. Arranging layer 322 by layer 322 and/or layer 322t on layer 322, a 3D item 1 may be formed. Reference 575 indicates the filament providing device, which here amongst others include the spool or roller and the driver wheels, indicated with reference 576.

Reference A indicates a longitudinal axis or filament axis. Reference C schematically depicts a control system, such as especially a temperature control system configured to control the temperature of the receiver item 550. The control system C may include a heater which is able to heat the receiver item 550 to at least a temperature of 50 °C, but especially up to a range of about 350 °C, such as at least 200 °C.

Alternatively, or additionally, the receiver plate may also be moveable in one or two directions in the x-y plane (horizontal plane). Further, the receiver plate may also be rotatable about z axis (vertical). Hence, the control system may move the receiver plate in one or more of the x-direction, y-direction, and z-direction.

Alternatively, the printer can have a head can also rotate during printing. Such a printer has an advantage that the printed material cannot rotate during printing.

Layers are indicated with reference 322, and have a layer height H and a layer width W.

Note that the 3D printable material is not necessarily provided as filament 320 to the printer head. Further, the filament 320 may also be produced in the 3D printer 500 from pieces of 3D printable material.

Reference D indicates the diameter of the nozzle (through which the 3D printable material 201 is forced).

Fig. lb schematically depicts in 3D in more detail the printing of the 3D item 1 under construction. Here, in this schematic drawing the ends of the filaments 321 in a single plane are not interconnected, though in reality this may be the case.

Reference H indicates the height of a layer. Layers are indicated with reference 203. Here, the layers have an essentially circular cross-section. Often, however, they may be flattened, such as having an outer shape resembling a flat oval tube or flat oval duct (i.e. a circular shaped bar having a diameter that is compressed to have a smaller height than width, wherein the sides (defining the width) are (still) rounded).

Hence, Figs la-lb schematically depict some aspects of a fused deposition modeling 3D printer 500, comprising (a) a first printer head 501 comprising a printer nozzle 502, (b) a filament providing device 575 configured to provide a filament 321 comprising 3D printable material 201 to the first printer head 501, and optionally (c) a receiver item 550. In Figs la-lb, the first or second printable material or the first or second printed material are indicated with the general indications printable material 201 and printed material 202, respectively. Directly downstream of the nozzle 502, the filament 321 with 3D printable material becomes, when deposited, layer 322 with 3D printed material 202. Fig. lc schematically depicts a stack of 3D printed layers 322, each having a layer height H and a layer width W. Note that the layer width and/or layer height may differ for two or more layers 322. Reference 252 in Fig. lc indicates the item surface of the 3D item (schematically depicted in Fig. lc).

Referring to Figs la-lc, the filament of 3D printable material that is deposited leads to a layer having a height H (and width W). Depositing layer 322 after layer 322, the 3D item 1 is generated.

When no wave guide used in a thin edge-lit down light, a high illuminance close to the LEDs and a dark area in the center is observed. To solve this issue, amongst others it is suggested to use of FDM to print transparent lines. Such lines comprise bends to act as leaky lightguides so that the light from the LEDs can be redirected towards the center to obtain homogeneous light extraction. This wavy (bent) lines are area filling and helps to fill a circular area uniformly with decreasing bending radius from sides to the center so that illuminance at the exit window is uniform. It also possible to use light scattering and wedge- shaped wave guide (thickness of the waveguide decreasing from the edge to the center) for obtaining uniform light extraction.

A thin round downlight may be equipped with a LED strip mounted at the circumference. It may be favorable to make the height of this downlight as small as possible with a high efficiency and a homogeneous illuminance distribution of the exit window. A lightguide plate with outcouple structures may be used to make this possible. This is expensive, not easy to digital process and should be redesigned for different sizes. For non- rotational shapes this lightguide solution is difficult or even impossible. It is for this reason that thin down light may make use of lightguides to obtain homogeneous illuminance distribution.

At a plant making use of FDM to produce luminaires, one may prefer to produce as much as possible the components using FDM. Bringing supplies from outside is expensive and costs time. Therefore, an FDM based solution is necessary for obtaining homogeneous light distribution from such thin light guides.

Amongst others, printing lines are suggested which run from the edges towards the center. In order to obtain uniform illumination, the lines which act as waveguides may not be straight but make bends. Bending of a light guide will increase the numerical aperture of this guide and will initiate leakage. Making the bending radius R small with respect to the diameter d of the light guide may enhance leakage. To make the appearance of the downlight homogeneous its necessary to redistribute the light from the LEDs over the total surface area of the downlight. By radial printing of lightguides with locally enhanced outcoupling it’s possible to tune the illuminance distribution of the front window. Figs 2a and 2b shows possible print paths. The embodiment of Fig. 2b may provide an enhanced outcoupling at smaller radial position. The embodiment of Fig. 2a may e.g. be relevant for radial configurations. Note that the embodiments of Figs. 2a and 2b may combined, i.e. with increasing distance from a second structure part an increase in radius and an increase in amplitude.

Here reference Wt indicates the total width of the structure 1202. In the embodiment of Fig. 2a, the total width Wt decreases with increasing distance from the first structure part 1211. Reference LE indicates the effective length of the structure 1202, i.e. the shortest distance from the first structure part 1211 to the second structure part 1212.

Reference LI indicates the length of the structure, following the structure from the first structure part 1211 to the second structure part 1212. This may be the length of the axis of elongation. The width of the structure 1202, indicated with W1 may be essentially the width W of a layer. Reference A1 indicates the amplitude (which decreases with increasing distance from the first structure part 1211). Reference B indicates bends (curvatures).

Fig. 2c schematically depicts an embodiment of the structure 1202, consisting of a stack of layers 322. The height of the structure 1202 is indicated with reference HI. As schematically shown in Fig. 2c, the first length LI or the effective length LE may be at least about 2 times, such as at least about 5 time, like at least about 10 times, such as even more especially at least about 30 times the width or height or diameter.

Fig. 2d schematically depicts in a cross-sectional view a structure 1202 consisting of a single layer 322. Hence, the height H of the layer 322 of the structure 1202 is the same as the structure height HIThe width Wi of the structure 1202 may be single W of the layer 322 or its multiples in other words Wi=n*W where n is an integer. When n=l then Wi=W. In the schematically depicted embodiments, the width W of the layer 322 of the structure 1202 is the same as the structure width Wl. Reference 1213 indicates the surface of the structure 1202. Hence, the 3D printed elongated structure may (also) comprise one or more layers 322 of 3D printed material 202. Such layers may be on top of each other and/or next to each other. The layers 322 may be side by side and/or on top of each other.

Fig. 2e also depicts a cross-sectional view. Here, it is clear that the length LI of the structure 1202 is along the axis of elongation A. Fig. 2f and 2g schematically depict embodiments wherein one or more layers 322, such as of the structure 1202 are core shell layers. Both may comprise 3D printed material 202, but of the core (202a) may have a different composition from the shell (202b). For instance, the former may be less scattering than the latter.

Fig. 2g schematically depicts an embodiment wherein an 3D printed elongated structures 1202 comprise a layer 322 (here the lowest and the one but highest) have a core shell structure, wherein the core is transmissive for radiation (having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation), wherein the shell has a variable shell thickness for facilitating light outcoupling from the core out of the layer via a shell part having a reduced shell thickness.

The structure 1202 is herein also described in relation to a light source 10 that provides light source light 11 to the first structure part 1211. At least part of the light source light 11 will escape from the structure 1202 via the structure surface 1213.

Hence, e.g. Figs. 2a-2e schematically depict an embodiment of the 3D item 1 comprising 3D printed material 202, wherein the 3D item 1 comprises one or more layers 322 of 3D printed material 202, wherein the 3D item 1 comprises one or more, especially a plurality, of 3D printed elongated structures 1202.

Each structure 1202 comprises 3D printed material 202, a first structure part 1211, a second structure part 1212, and an elongated structure surface 1213 between the first structure part 1211 and the second structure part 1212.

The 3D printed material 202, e.g. polysiloxane, is transmissive for radiation 11 having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein one or more of a (a) shape of one or more of the elongated structures 1202 and (b) the elongated structure surface 1213 of one or more of the elongated structures 1202 are chosen such that a first part of the radiation 11 propagating through the elongated structure 1202 from the first structure part 1211 to the second structure part 1212 escapes from the elongated structure 1202 via the elongated structure surface 1213.

The 3D printed elongated structure 1202 has a structure height HI. One or more of the 3D printed elongated structures 1202 comprise curvatures B in a plane P perpendicular to the structure height HI. The 3D printed elongated structures 1202 have a structure width Wl. Especially, one or more of the curvatures B have radii r, wherein the radii r and the structure width Wl may especially be chosen such that the first part of the radiation 11 escapes from the elongated structures 1202 via the elongated structure surfaces 1213 at one or more of the curvatures B.

Referring to Fig. 2a, the radii r of one or more 3D printed elongated structures 1202 decrease with increasing distance from the curvatures B from the first structure part 1211

Referring to e.g. Figs. 2a, 2b, 2c, 2e, the printing direction may especially be parallel to an axis of elongation of a respective 3D printed structure 1202. Further, referring to these figures, but also other figures, the first length LI (between the first structure part 1211 and the second structure part 1212) measured along an axis of elongation A of the 3D printed elongated structure 1202 may be at least 1 cm, such as at least 2 cm, like at least 5 cm.

Hence, amongst others the invention provides an FDM printed light guide with a‘wavy’ structure. Outcoupling from this light guide may be chosen as function of radial position as shown. This wavy structure may be area filling and may be used to fill a circular area for uniform with decreasing bending radius from sides to the center (see also below).

Fig. 3a (and in embodiments also Fig. 3b) show an embodiment, wherein the elongated structures 1202 are configured in a radial configuration. In this way, the light intensity at every point on a light emitting surface from a lighting device, like e.g. a diffusor (see also below) may essentially be uniform. Here, only a half of a disc-shaped lighting device 1000 is schematically depicted. Reference 2 indicates a luminaire.

In this way, e.g. a downlight may be provided that may be relatively thin.

Figs. 3a and 3b also schematically depict embodiments of a lighting device 1000. Fig. 3b may e.g. schematically depicts a cross-section of a disc-like lighting device 1000

The lighting device 1000 comprises the 3D item 1 as defined herein, and one or more, especially a plurality of light sources 10 configured to generate radiation 11 having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation. The 3D printed elongated structure(s) 1202 are configured in a light receiving relationship with one or more light sources 10 such that at least part of the radiation 11 propagates in a direction from the first structure part 1211 to the second structure part 1212.

The lighting device 1000 may comprise a plate-like shape 1250, wherein the first structure parts 1211 define an edge face 1251. The light sources 10 may be configured upstream of the edge face 1251. The lighting device 1000 further comprises a reflector 1260 and a radiation transmissive diffusor 1270, wherein the plurality of 3D printed elongated structures 1202 are configured between the reflector 1260 and the diffusor 1270, wherein the reflector 1260 is configured to reflect at least part of the radiation 11 that has escaped from one or more of the 3D printed elongated structures 1202 in a direction of the diffusor 1270.

For uplighting and downlighting, lighting device 1000 may further comprise two radiation transmissive diffusors 1270, wherein the plurality of 3D printed elongated structures 1202 are configured between the two diffusors 1270.

As shown, the elongated structures 1202 may be configured in a radial configuration, and wherein the light sources 10 are configured in a circle surrounding the first structure parts 1211 of the 3D printed elongated structures 1202.

Fig. 3c schematically depict embodiments of a plurality of structures 1202, which may be printed with continuous printing. In such embodiments the first structure part 1211 and the second structure part 1212 may be connected with other parts. Here, the first structure parts may be light incoupling or light entrance point for the light source light, and the second structure parts 1212 may be those parts closest to a center of a disc-shape element or device.

It also possible to use light scattering area on the sides of the wave guide with increasing density towards the center can help getting radial light extraction as shown in Fig. 4a. Making the wave guide to have wedge-shape (thickness of the waveguide decreasing from the edge to the center) for obtaining uniform radial light extraction. Fig. 4b shows side view of such wave guide. In order to get tangential uniformity, it is possible to add side branches to the wave guide as shown in Fig. 4c.

The light intensity at every point on the surface from elongated structure may essentially be uniform.

One or more of the following may apply: (i) the elongated structure surface 1213 of one or more 3D printed elongated structures 1202 comprise radiation outcoupling structures 1215 for facilitating outcoupling of radiation 11 from the one or more elongated structures 1202 via the elongated structure surface 1213 (see Fig. 4a), and (ii) one or more 3D printed elongated structures 1202 comprise one or more 3D printed structure branches 1252, branching away from the 3D printed elongated structure 1202 (see Fig. 4c). Such branches may have dimensions like (effective) length, width and height, or diameter, of which one or more may be identical to the main part of the structure, and/or of which one or more may be smaller than of the main part of the structure. In general, at least the latter applies. Figs. 4d-4e schematically depicts different types of first structure parts 1211 or light entrance points. Note that in the latter embodiments, these first structure parts 1211 are connected via (other) 3D printed material.

Fig. 4f schematically depicts an embodiment of the 3D printed elongated structure comprising shape irregularities, here indicated with reference 1215 (also used for outcoupling structures). In the top part, very schematically the intensity in Watt of the light source light 11 within the 3D printed elongated structure along the first length LI of the 3D printed elongated structure is indicated. There is an essentially constant decrease, which may indicate an essentially even outcoupling. On the left, e.g. the intensity may be the initial intensity in the structure at the first structure end 1211, i.e. Wo ; at the end the intensity in watt is Wi.

The term“substantially” herein, such as“substantially consists”, will be understood by the person skilled in the art. The term“substantially” may also include embodiments with“entirely”,“completely”,“all”, etc. Hence, the adjective substantially may also be removed. Where applicable, the term“substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term“comprise” includes also embodiments wherein the term “comprises” means“consists of’. The term“and/or” especially relates to one or more of the items mentioned before and after“and/or”. For instance, a phrase“item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of' but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention also provides a control system that may control the apparatus or device or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the apparatus or device or system, controls one or more controllable elements of such apparatus or device or system.

The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

It goes without saying that one or more of the first (printable or printed) material and second (printable or printed) material may contain fillers such as glass and fibers which do not have (to have) influence on the on T_g or T_m of the material(s).

Hereinbefore, the following examples have been described:

1. A method for producing a 3D item (1) by means of fused deposition modelling, the method comprising a 3D printing stage comprising layer-wise depositing an extrudate (321) comprising 3D printable material (201), to provide the 3D item (1) comprising 3D printed material (202), wherein the 3D item (1) comprises one or more layers (322) of 3D printed material (202), wherein the method comprises:

providing during the 3D printing stage a plurality of 3D printed elongated structures (1202), each comprising 3D printed material (202), a first structure part (1211), a second structure part (1212), and an elongated structure surface (1213) between the first structure part (1211) and the second structure part (1212), wherein the 3D printed material (202) is transmissive for radiation (11) having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein one or more of (a) a shape of one or more of the elongated structures (1202) and (b) the elongated structure surface (1213) are chosen such that a first part of the radiation (11) propagating through the elongated structure (1202) from the first structure part (1211) to the second structure part (1212) escapes from the elongated structure (1202) via the elongated structure surface (1213).

2. The method according to example 1, wherein one or more of the 3D printed elongated structures (1202) have a structure height (HI), wherein the method further comprises printing the one or more 3D printed elongated structures (1202) with one or more curvatures (B) in a plane (P) perpendicular to the structure height (HI), and wherein the one or more 3D printed elongated structures (1202) are selected such that a second part of the radiation (11) propagating through each of the one or more elongated structures (1202) from the first structure part (1211) to the second structure part (1212) reaches the second structure part (1212), wherein an intensity ratio (Watt/Watt) of the second part to the first part is equal to or smaller than 0.1, and wherein a first length (LI) between the first structure part (1211) and the second structure part (1212) measured along an axis of elongation (A) of the 3D printed elongated structure (1202) is at least 1 cm.

3. The method according to any one of the preceding examples, wherein one or more of the 3D printed elongated structures (1202) have a structure height (HI), wherein the method further comprises printing the one or more 3D printed elongated structures (1202) with one or more curvatures (B) in a plane (P) perpendicular to the structure height (HI), wherein the one or more of the 3D printed elongated structures (1202) have a structure width (Wl), wherein the method comprises printing the one or more 3D printed elongated structures (1202) with (i) radii (r) of the one or more curvatures (B) and (ii) the structure width (Wl) chosen such that the first part of the radiation (11) escapes from the elongated structures (1202) via the elongated structure surfaces (1213) at one or more of the curvatures (B), and wherein the radii (r) and the structure width (Wl) having a ratio selected from the range of 0.5<r/Wl£20.

4. The method according to example 3, wherein the method comprises printing the one or more 3D printed elongated structures (1202) with radii (r) which decrease with increasing distance from the curvatures (B) from the first structure part (1211).

5. The method according to any one of the preceding examples, wherein the method comprises one or more of: (i) printing one or more 3D printed elongated structures (1202) with elongated structure surfaces (1213) comprising radiation outcoupling structures for facilitating outcoupling of radiation (11) from the one or more elongated structure (1202) via the elongated structure surfaces (1213), (ii) printing one or more 3D printed elongated structures (1202) with one or more 3D printed structure branches (1252), branching away from the 3D printed elongated structure (1202), and iii) printing one or more 3D printed elongated structures (1202) with one or more shape irregularities by reducing a flow of the 3D printable material during printing.

6. The method according to any one of the preceding examples, wherein the method comprises printing the elongated structures (1202) in a radial configuration, wherein further a printing direction is parallel to an axis of elongation of a respective 3D printed structure (1202).

7. The method according to any one of the preceding examples, wherein the 3D printable material (201) and the 3D printed material (202) comprise one or more of polycarbonate (PC), styrene-acrylonitrile resin (SAN), amorphous polytethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), poly (methyl methacrylate) (PMMA), polystyrene (PS), polyurethane (PU), polysiloxane, styrene acrylic copolymers (SMMA), and low crystalline transparent polypropylene and polyethylene. 8. A 3D item (1) comprising 3D printed material (202), wherein the 3D item (1) comprises one or more layers (322) of 3D printed material (202), wherein the 3D item (1) comprises a plurality of 3D printed elongated structures (1202), each comprising 3D printed material (202), a first structure part (1211), a second structure part (1212), and an elongated structure surface (1213) between the first structure part (1211) and the second structure part (1212), wherein the 3D printed material (202) is transmissive for radiation (11) having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein one or more of (a) a shape of one or more of the elongated structures (1202) and (b) the elongated structure surface (1213) of one or more of the elongated structures (1202) are chosen such that a first part of the radiation (11) propagating through the elongated structure (1202) from the first structure part (1211) to the second structure part (1212) escapes from the elongated structure (1202) via the elongated structure surface (1213).

9. The 3D item (1) according to example 8, wherein one or more of the 3D printed elongated structures (1202) have a structure height (HI), wherein the one or more of the 3D printed elongated structures (1202) comprise curvatures (B) in a plane (P) perpendicular to the structure height (HI), wherein the 3D printed elongated structures (1202) have a structure width (Wl), wherein one or more of the curvatures (B) have radii (r), wherein (i) the radii (r) and (ii) the structure width (Wl) are chosen such that the first part of the radiation (11) escapes from the elongated structures (1202) via the elongated structure surfaces (1213) at one or more of the curvatures (B); and wherein a first length (LI) between the first structure part (1211) and the second structure part (1212) measured along an axis of elongation (A) of the 3D printed elongated structure (1202) is at least 1 cm.

10. The 3D item (1) according to example 9, wherein the radii (r) of one or more 3D printed elongated structures (1202) decrease with increasing distance from the curvatures (B) from the first structure part (1211).

11. The 3D item (1) according to any one of the preceding examples 8-10, wherein one or more of the following applies: (i) the elongated structure surface (1213) of one or more 3D printed elongated structures (1202) comprise radiation outcoupling structures for facilitating outcoupling of radiation (11) from the one or more elongated structures (1202) via the elongated structure surface (1213), (ii) one or more 3D printed elongated structures (1202) comprise one or more 3D printed structure branches (1252), branching away from the 3D printed elongated structure (1202), (iii) one or more 3D printed elongated structures (1202) comprise shape irregularities, and (iv) one or more 3D printed elongated structures (1202) comprise a layer (322) have a core-shell structure, wherein the core is transmissive for radiation (11) having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein the shell has a variable shell thickness for facilitating light outcoupling from the core out of the layer via a shell part having a reduced shell thickness.

12. The 3D item (1) according to any one of the preceding examples 8-11, wherein the elongated structures (1202) are configured in a radial configuration, and wherein an effective length (LE), defined as a shortest length between the first structure part (1211) and the second structure part (1212) is at least 50% of the radius.

13. A lighting device (1000) comprising the 3D item (1) according to any one of the preceding examples 8-12, and a plurality of light sources (10) configured to generate radiation (11) having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation, wherein the plurality of 3D printed elongated structures (1202) are configured in a light receiving relationship with the plurality of light sources (10) such that at least part of the radiation (11) propagates in a direction from the first structure part (1211) to the second structure part (1212).

14. The lighting device (1000) according to example 13, comprising a plate-like shape (1250), wherein the first structure parts (1211) define a edge face (1251), wherein the light sources (10) are configured upstream of the edge face (1251), wherein the lighting device (1000) further comprises a reflector (1260) and a radiation transmissive diffusor (1270), wherein the plurality of 3D printed elongated structures (1202) are configured between the reflector (1260) and the diffusor (1270), wherein the reflector (1260) is configured to reflect at least part of the radiation (11) that has escaped from one or more of the 3D printed elongated structures (1202) in a direction of the diffusor (1270), and wherein the 3D printed material (202) comprises one or more of polycarbonate (PC), styrene- acrylonitrile resin (SAN), amorphous polytethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), poly(methyl methacrylate) (PMMA), polystyrene (PS), polyurethane (PU), polysiloxane, styrene acrylic copolymers (SMMA), and low crystalline transparent polypropylene and polyethylene.

15. The lighting device (1000) according to any one of the preceding examples 13-14, wherein the elongated structures (1202) are configured in a radial configuration, and wherein the light sources (10) are configured in a circle surrounding the first structure parts (1211) of the 3D printed elongated structures (1202).

Claims

CLAIMS:

1. A light guide (1) for use in a lighting device (1000), wherein the light guide (1) comprises a plurality of elongated structures (1202), each elongated structure (1202) having an elongated structure surface (1213) between a first structure part (1211) and a second structure part (1212), the first structure parts (1211) together defining an edge face (1251) of the waveguide (1),

wherein each elongated structure (1202) has a structure height (HI) and a structure width (Wl),

wherein each elongated structure (1202) comprise curvatures (B) in a plane (P) perpendicular to the structure height (HI), the curvatures (B) having radii (r),

wherein the radii (r) and the structure width (Wl) are chosen such that radiation (11) propagating through the elongated structure (1202) from the first structure part (1211) to the second structure part (1212) can escape from the elongated structure (1202) via the elongated structure surface (1213) at one or more of the curvatures (B).

2. The light guide (1) according to claim 1, wherein a first length (LI) between the first structure part (1211) and the second structure part (1212) measured along an axis of elongation (A) of the elongated structure (1202) is at least 1 cm.

3. The light guide (1) according to claim 2, wherein the radii (r) and the structure width (Wl) have a ratio in a range of 0.5 to 20.

4. The light guide (1) according to any one of claims 2 and 3, wherein the radii (r) of the elongated structures (1202) decrease with increasing distance from the curvatures (B) from the first structure part (1211).

5. The light guide (1) according to any one of the claims 1 to 4, wherein the elongated structures (1202) are configured in a radial configuration, and wherein an effective length (LE), defined as a shortest length between the first structure part (1211) and the second structure part (1212) is at least 50 % of the radius.

6. The light guide (1) according to any one of the claims 1 to 5, wherein one or more of the following applies:

(i) the elongated structure surface (1213) of one or more elongated structures (1202) comprises radiation outcoupling structures for facilitating outcoupling of radiation (11) from the one or more elongated structures (1202) via the elongated structure surface (1213),

(ii) one or more elongated structures (1202) comprise one or more structure branches (1252), branching away from the elongated structure (1202),

(iii) one or more elongated structures (1202) comprise shape irregularities, and

(iv) one or more elongated structures (1202) comprise a layer (322) having a core shell structure, wherein the core is transmissive for the radiation (11), and wherein the shell has a variable shell thickness for facilitating light outcoupling from the core via a shell part having a reduced shell thickness.

7. A lighting device (1000) comprising the light guide (1) according to any one of claims 1 to 6, wherein the lighting device (1000) further comprises:

a plurality of light sources (10) configured to generate radiation (11) having intensity at one or more wavelengths in one or more wavelength ranges selected from UV radiation, visible radiation, and infrared radiation,

a reflector (1260), and

a diffusor (1270),

wherein the plurality of light sources (10) are configured upstream of the edge face (1251) of the light guide (1) so that, in operation, at least part of the radiation (11) generated by the plurality of light sources (10) propagates through the elongated structures (1202) in a direction from the first structure part (1211) to the second structure part (1212), and

wherein the light guide (1) is arranged such that the plurality of elongated structures (1202) is configured between the reflector (1260) and the diffusor (1270) so that, in operation, at least part of the radiation (11) that has escaped from the elongated structures (1202) is reflected by the reflector (1260) in a direction towards the diffusor (1270).

8. The lighting device (1000) according to claim 7, wherein, in operation, a first part of the radiation (11) propagating through the elongated structures (1202) in a direction from the first structure part (1211) to the second structure part (1212) escapes from the elongated structures (1202) via the elongated structure surfaces (1213).

9. The lighting device (1000) according to claim 8, wherein, in operation, a second part of the radiation (11) propagating the elongated structures (1202) in a direction from the first structure part (1211) to the second structure part (1212) reaches the second structure part (1212), wherein an intensity ratio (Watt/Watt) of the second part to the first part is equal to or smaller than 0.1, and wherein each elongated structure (1202) has a first length (LI) of at least 1 cm between the first structure part (1211) and the second structure part (1212) measured along an axis of elongation (A) of the elongated structure (1202).

10. The lighting device (1000) according to any one of claims 7 to 9, wherein the elongated structures (1202) are configured in a radial configuration, and wherein the light sources (10) are configured in a circle surrounding the first structure parts (1211) of the elongated structures (1202).

11. A method for producing the light guide (1) according to any one of claims 1 to 6 by means of fused deposition modelling, the method comprising a 3D printing stage comprising layer-wise depositing an extrudate (321) comprising 3D printable material (201), to provide the lightguide (1) comprising 3D printed material (202), wherein the light guide (1) comprises one or more layers (322) of 3D printed material (202), and wherein the method comprises providing during the 3D printing stage the plurality of elongated structures (1202), each comprising 3D printed material (202).

12. The method according to claim 11, wherein the method comprises printing the elongated structures (1202) in a radial configuration, and wherein each elongated structure (1202) is printed in a printing direction that is parallel to an axis of elongation of the elongated structure (1202).

13. The method according to any one of claims 11 and 12, wherein the 3D printable material (201) and the 3D printed material (202) comprise one or more of polycarbonate (PC), styrene-acrylonitrile resin (SAN), amorphous polytethylene

terephthalate (PET), acrylonitrile butadiene styrene (ABS), poly (methyl methacrylate) (PMMA), polystyrene (PS), polyurethane (PU), polysiloxane, styrene acrylic copolymers (SMMA), and low crystalline transparent polypropylene and polyethylene.