WO2023217885A1

WO2023217885A1 - An optical plate

Info

Publication number: WO2023217885A1
Application number: PCT/EP2023/062463
Authority: WO
Inventors: Jing Yang; Xiaoqing Duan; Mo Shen; Qing Zhang; Xue Chen LI; Yue Hua ZHANG
Original assignee: Signify Holding B.V.
Priority date: 2022-05-13
Filing date: 2023-05-10
Publication date: 2023-11-16

Abstract

An optical plate comprising a first surface and an opposite second surface, wherein the first surface is defined by a micro-structure arrangement of the optical plate. This micro-structure arrangement comprises an array of polygonal pyramids. The second surface is planar. The optical plate comprises a polymer material doped with diffusive particles, so that transmittance of the optical plate is in the range of 67% -72%.

Description

An Optical Plate

FIELD OF THE INVENTION

This invention relates to an optical plate used in LED downlight.

BACKGROUND OF THE INVENTION

In the field of lighting, it is common for a lighting device (such as a downlight) to comprise a diffuser plate as a lamp mask, i.e., to filter the output of the lighting device. The diffuser plate will diffuse or scatter light emitting by a light emitting arrangement of the lighting device to provide more uniform illumination of an area.

For improved performance, some lighting devices are also provided with an anti-glare plate, to reduce glare to an individual in the vicinity of the lighting device. Providing the anti-glare plate substantially increases the material cost and difficulty of assembling the lighting device.

WO 2015104247A1 discloses a light diffusion plate which comprises a core layer formed with a thermoplastic resin containing diffusion agents and having an optical transmission property, and arranged in front of a light source; and a pattern layer configured with patterns formed on the surface of the core layer.

US 20080310171 Al discloses an optical sheet which comprises a continuous phase comprising a transparent material and a dispersed phase dispersed in the continuous phase, and has a first surface and a second surface. At least one of the first surface and the second surface forms a prismatic surface of a prism portion constituting portion of the sheet, and the prism portion has a plurality of prism units, each having a triangular cross-section, formed regularly in a longitudinal and/or width direction of the sheet.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided an optical plate comprising: a microstructure arrangement formed of a plurality of polygonal pyramids; a first surface; and an opposite second surface. The first surface is defined by the micro-structure arrangement; the second surface is planar; and the optical plate comprises a polymer material doped with scattering particles, such that the transmittance of the optical plate is in the range of 67% to 72%.

The proposed optical plate is able to perform the functions of both the diffuser and an anti-glare plate in a single component. This provides a more materially efficient light filtering/modifying structure that can also increase an ease of assembling any lighting device comprising such a structure.

In particular, proposed embodiments have recognized that an optical plate having the identified structure (i.e., comprising the micro-structure arrangement) but with the defined transmittance will provide an optical plate with good/desirable light uniformity output as well as reduced glare. The proposed approach thereby overcomes the issues with existing lighting devices.

It’s the inventors’ insight that uniformity and preventing glare are two contradictory optical characteristics of the output light of a lighting device, e.g., a downlight, to be achieved. It’s observed that when the transmittance of the optical plate increases, uniformity decreases, however the performance of preventing glare increases. To achieve a compromised light output for the lighting device, the optimal range of the transmittance of the optical plate is chosen at 67% - 72%.

Preferably, the surface roughness Ra of the first surface is less than or equal to 0.063 pm. This increases the performance of the light scattering performed by the microstructure arrangement.

In some examples, the surface roughness Ra of the second surface (120) is less than or equal to 0.063 pm. Providing a smooth second surface can compensate for any overdoping of the optical plate, e.g., to reduce the scattering of the optical plate and increase transmittance.

In some examples, the second surface is textured to have a surface roughness Ra of between 0.08pm and 3.2pm. This approach can compensate for any under-doping of the optical plate, e.g., to increase the scattering performed by the optical plate and reduce transmittance.

In some examples, the thickness of the optical plate is between 0.5mm and 2mm. This provides a compact, light and materially-efficient optical plate for reduced material cost and ease of assembly. This effect is enhanced in embodiments in which the thickness of the optical plate is between 0.6mm and 1.7mm.

In some examples, the height of each polygonal pyramid is between 16% and optical plate. This approach will increase an ease of manufacturing the optical plate and assembling the optical plate into a lighting device.

In some examples, the height of each polygonal pyramid is between 0.1mm and 0.5mm. This provides polygonal pyramids that are able to contribute to the scattering of light output by the optical plate, without resulting in a brittle or dangerous surface for an individual installing a lighting device comprising such an optical plate.

In some examples, the optical plate comprises a polymer material doped with scattering particles such that the transmittance of the optical plate is in the range of 65% to 81%, e.g., 70% to 80%. This range ensures a preferred uniformity of light is output by the optical plate, and further reduces glare.

The optical plate may comprise a polymer material doped with scattering particles such that the transmittance of the optical plate is in the range of 65% to 81%. It is preferable that the transmittance of the optical plate is in the range of 65% to 71% for polycarbonate (PC) material and 77% to 81% for polypropylene (PP) material. This range ensures an even more preferred uniformity of light is output by the optical plate, and yet further reduces glare.

In some examples, each polygonal pyramid is formed of a plurality of pyramid sides that meet at an apex; and for each polygonal pyramid, the angle between any two pyramid sides at the apex is no less than 100°. It has been herein recognized that the angle between two pyramid sides (the apex angle) has an influence on the glare for light transmitted through the optical plate. In particular, an increase to the apex angel will reduce glare.

In some examples, the angle between any two pyramid sides at the apex (i.e., the apex angle) is no less than 110°. This further enhances the above-mentioned reduction of glare.

Preferably, the angle between any two pyramid sides at the apex is no more than 120°.

There is also provided a lighting device, comprising a housing, a light source, an electronic board, and an optical plate according as previously described. The optical plate may be mounted on a light exit window of the housing and over the light source.

In preferred examples, a distance between the light source and the optical plate is between 25 and 35mm.

The lighting device may be formed as a downlight.

There is proposed a semi-diffused material, having micro-structures arrayed on the emitting side of plate, the other side being planar, both sides are smooth surface with surface roughness at Ra < 0.063p.m. The new type of semi-diffused prism plate integrates the two functions of diffusion and anti-glare on the basis of one board as well as effectively reducing the cost.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 shows a cut-off view of a downlight with the optical plate according to the present disclosure;

Figure 2 shows a perspective view of the optical plate according to the present disclosure;

Figure 3 shows a sectional view of one embodiment of the optical plate according to the present disclosure;

Figure 4 shows a sectional view of another embodiment of the optical plate according to the present disclosure;

Figure 5 provides a sectional view of a portion of an optical plate;

Figure 6 is a graph illustrating a relationship between transmittance and a change in glare;

Figure 7 is a graph illustrating a relationship between a pyramid apex angle and glare;

Figure 8 is a graph illustrating relationships between transmittance and changes in glare and uniformity; and

Figure 9 is the configuration of testing on glare.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

There is proposed an optical plate comprising a first surface and an opposite second surface, wherein the first surface is defined by a micro-structure arrangement of the optical plate. This micro-structure arrangement comprises an array of polygonal pyramids. The second surface is planar. The optical plate comprises a polymer material doped with diffusive particles, so that transmittance of the optical plate is in the range of 65% -85%.

The present disclosure provides an optical plate, which may be used in a lighting device. The proposed optical plate has improved glare properties (i.e., reduced glare) compared to existing diffusers for a lighting device. In particular, the proposed optical plate can be used to replace existing diffusers to achieve a lighting device with reduced glare.

Embodiments are based on the realization that an appropriately configured optical plate can be used to perform the functions of both a light diffuser and an anti-glare plate. In particular, by providing a micro-structure arrangement that defines one side of the optical plate (in the manner of a conventional light diffuser), but modifying the transmittance of the optical plate, an anti-glare functionality can be achieved without significantly impacting on the scattering and uniformity performance of the optical plate.

Disclosed optical plates can be used in lighting devices, and find particular use in downlights where high light uniformity with minimal glare is desired. Embodiments can be employed in any suitable industry, including commercial, domestic and clinical environments.

Figure 1 illustrates a lighting device 10 in the form of a downlight. A downlight is a light designed to be mounted in a ceiling for illuminating a room or area in a downwards direction.

The lighting device 10 comprises a housing 11, a light source 12, an electronic board 13 and an optical plate 100.

The housing 11 holds and/or supports the other components of the lighting device 10. In particular, the housing 11 may house or support an electronic board 13 that carries a light source 12.

The light source 12 comprises any number of suitable light emitting elements for a lighting device, such as one or more light emitting diodes (LEDs) and/or one or more halogen bulbs. If the light source 12 comprises one or more LEDs, the lighting device 10 is formed as an LED downlight.

The electronic board 13 comprises or carries driving and/or control circuitry for the light source 12. Approaches for driving and/or controlling the light source are established in the art, and are not described for the sake of conciseness.

The housing 11 defines a light exit window 14, from which light emitted by the light source 12 is emitted out of the lighting device 10.

The optical plate 100 is positioned on or in the light exit window 14 defined by the housing. Thus, the optical plate 100 receives and transmits light that exits the lighting device 10. The optical plate 100 is therefore able to control or refine one or more optical characteristics of light output by the lighting device 10.

The optical plate 100 may be held in the light exit window by a supporting element 15 (which may also define the bounds of the light exit window 14). Such supporting elements are known in the art, and are configured to grip or support the sides of an optical plate. In preferred examples, the distance d_s between an outermost plane 151 of the supporting element 15 and the optical plate of the optical plate 100 may be in the region of 1 to 2mm, e.g., between 1mm and 2mm, e.g., between 1.2mm and 1.8mm. This reduces the glare of light emitted by the lighting device, by at least partially blocking light emitted at certain angles from the light exit window 14.

In the illustrated example, the supporting element 15 is shaped in the form of a ring or annulus that supports the optical plate 100 in the center thereof.

Further optional features of the lighting device 10 are illustrated in Figure 1.

One optional feature is a mount 16, configured to hold the lighting device to a surface or aperture. In the illustrated example, the mount 16 is a spring-mounted securing system for securing the lighting device within an aperture (e.g., in a ceiling or wall). This provides a downlight functionality.

Optionally, the distance d between the optical plate 100 and the light source 12 is between 25 and 35 mm. This provides sufficient distance for a light source 12 to spread light across the optical plate 100, for improved diffusion, whilst remaining sufficiently compact for use in a downlight application.

For the sake of conciseness, additional components of the lighting device (such as power circuitry, socket connectors etc.) have not been described or illustrated. However, the skilled person would readily appreciate that a lighting device may comprise such standard elements in the usual manner. As previously mentioned, the present disclosure proposes a new form of optical plate 100, which is itself an embodiment of the invention. An optical plate 100 is an optical sheet or piece of material that modifies the optical properties of light passing therethrough. In the context of the present disclosure, the optical plate 100 is configured to modify the glare and uniformity of light transmitted through the optical plate 100.

Figures 2, 3 and 4 illustrate an optical plate 100 according to an embodiment. In particular, Figure 2 provides a perspective view of a portion of an optical plate 100, with Figures 3 and 4 providing cross-sectional views of different versions of the optical plate 100.

The proposed optical plate 100 is effectively a semi-diffused prism plate. The proposed optical plate visually resembles a conventional anti -glare plate (having a surface 110 defined by a micro-structure arrangement 111), but with reduced transparency compared to existing anti-glare plates. The proposed structure performs both a light diffusing functionality and an anti -glare functionality.

In particular, the optical plate comprises a first surface 110 and an opposite second surface 120, 420. The optical plate 100 also comprises a micro-structure arrangement 111, which defines the first surface 110.

Conceptually, the optical plate 100 can be considered to comprise a main body 130 and a micro-structure arrangement 111, with the micro-structure arrangement 111 defining the first surface 110 and the main body 130 defining the second surface 120. The microstructure arrangement 111 may be formed integrally with the main body 130, or separately thereto (e.g., but coupled to the main body 130). Thus, the microstructure arrangement 111 and the main body 130 may formed of a same material or different materials.

In use, such as in the previously described lighting device, the second surface is the surface that receives light from a light source and the first surface is the surface that emits light out of the lighting device. Thus, the first surface is an emitting surface and the second surface is a receiving surface. Put another way, the micro-structure arrangement is located on the side of the optical plate that emits light towards the eyes of a user or individual, i.e., on the emitting surface of the optical plate.

The first surface 110 of the optical plate 100 is defined by the micro-structure arrangement 111.

In the illustrated example, a first side of a main body 130 of the optical plate 100 defines the second surface 120 and the micro-structure arrangement 111 (coupled to a second, different side of the main body 130) defines the first surface 110. The microstructure arrangement 111 is formed from a plurality of polygonal pyramids. The microstructure arrangement 111 could be formed of triangular pyramids, square pyramids (i.e., conventional pyramids), pentagonal pyramids, hexagonal pyramids and so on. The micro-structure arrangements 111 performs a glare reducing function for the optical plate 100.

Approaches for forming a micro-structure arrangement 111 to define a first surface 110 of the optical plate 100 will be apparent to the skilled person.

For instance, the micro-structure arrangement could be formed integrally with the main body 130 of the optical plate. For instance, the micro-structure arrangement could be formed during an original single-step manufacturing method together with the main body 130 of the optical plate 100 (e.g., in a hot press or injection-molding technique) or formed by etching a main body 130.

In some examples, the micro-structure arrangement 111 may be initially formed separately from a main body 130 of the optical plate 100, before being coupled thereto. This can be performed, for instance, using a roll-to-roll extrusion procession technology.

In yet other examples, the micro-structure arrangement 111 is formed directly on the main body 130 of the optical plate 100. This can be achieved, for instance, using a deposition technique or the like (with optional additional etching).

The second surface 120 is planar. Thus, the second surface 120 is not defined by a micro-structure arrangement. As will be later explained, the second surface may have a roughened texture, but this is not essential.

The optical plate 100 comprises a polymer material doped with scattering particles, such that the transmittance of the optical plate is in the range of 65% to 85%. An alternative label for scattering particles is diffusive particles, as they act to scatter/diffuse light transmitted through the optical plate 100.

In particular, it is preferable that at least the main body 130 of the optical plate 100 comprises or be formed from a polymer material doped with scattering particles to achieve the desired transmittance. Optionally, the micro-structure arrangement 111 may also comprise or be formed from a polymer material doped with scattering particles to achieve the desired transmittance.

Thus, in preferable examples, the entirety of the optical plate is formed of polymer material doped with scattering particles, such that the transmittance of the optical plate is in the range of 65% to 85%. Use of a polymer material doped with scattering particles provides the optical plate with a scattering functionality.

Suitable examples of polymer materials for use as the optical plate include transparent PP, PC, PS or PMMA. An optical plate of such material could be produced using an extrusion (e.g., a roll-to-roll extrusion procession technology), hot press or injectionmolding technique.

As one example, the transmittance of the optical plate 100 is preferably in the range of 65% to 71% when (at least the main body 130 is) formed of polycarbonate (PC) material and 77% to 81% when (at least the main body 130 is) formed of polypropylene (PP) material. The skilled person would be readily capable of identifying other ranges for other forms of polymer materials. That being said, it is noted that a range of 65% to 85% is particularly suited to achieving the desired advantages of the present disclosure for a wide variety of different polymer materials, with a range of 65% to 81% exhibiting even more improved properties.

Suitable scattering particles for use in the optical plate 100 (e.g., to perform scattering whilst achieving the desired transmittance) include nano Barium sulfate, Silicon dioxide, calcium carbonate, organic silicon, acrylic resin and so on. The diameter of the scattering particles may be between 1pm to 10pm. The density of the scattering particles will be related to the type and size of the scattering particles selected.

The aforementioned parameters will combine to define or determine the transmittance of the optical plate 100. In particular, a natural consequence of increased scattering (e.g., by increasing the concentration of scatters within the optical plate) is reduced transmittance. Appropriate selection of the above-identified parameters thereby enables the transmittance of the optical plate 100 to be tuned to lie in the region of 65%-85%.

Approaches for doping polymer materials with scattering particles will be apparent to the skilled person, and could include diffusion and/or implantation techniques. The term “doping” is here used to refer to the intentional introduction or provision of foreign particles (namely, scattering particles) into the polymer material to modify the properties (here, at least the transmittance and diffusion) of the polymer material. An alternative label to the term “doping” is blending.

Approaches for testing the transmittance of an optical plate are well known in the art. For instance, the transmittance could be tested according to standard ASTM DI 003 or GB/T 2410-2008, using one or more test devices such as a light transmittance meter or a haze meter. It will be appreciated that the introduction of scattering particles into the optical plate will decrease transmissivity whilst increasing scattering/diffusion. Thus, the more scattering particles present in the optical plate, the less transmissive the optical plate.

It has been herein recognized that uncontrolled increases to scattering (to achieve more uniform light distribution) will disadvantageously increase the perceived glare provided by light output through the optical plate. In particular, it has been recognized that there is a relationship between glare and transmittance of an optical plate. Transmittance is at least partially dependent upon the amount of scattering performed by the optical plate.

More particularly, it has been herein recognized that an optical plate with the above-identified structure (i.e., comprising the proposed micro-structure) with a transmittance in the region of 65%-85% will provide a good compromise between reduced glare whilst maintaining good light distribution for uniform illumination of a space, i.e., achieve a desired scattering profile.

Figures 3 and 4 conceptually illustrate two different versions of the optical plate.

In Figure 3, both the first 110 and second 120 surfaces are optically polished, e.g., to have a surface roughness Ra of less than 0.063 pm.

In Figure 4, the first surface 110 is optically polished, e.g., to have a surface roughness Ra of less than 0.063 pm. The second surface is roughened or otherwise configured to have a larger surface roughness, e.g., a surface roughness Ra of between 0.08pm and 3.2pm.

Approaches for optically polishing a surface are well known to the skilled person. Example approaches for roughening a surface include electrical discharge machining (EDM) or chemical etching. Providing a rough surface increases the scattering of light through the optical plate, and could be used to reduce the amount of doping required to achieve an optical plate having a transmittance in the region of 65% to 85%.

The choice of whether to optically polish or roughen the second surface may depend upon the doping of the optical plate 100 with scattering particles. For instance, if too many scattering particles have been used to dope the optical plate (e.g., such that transmittance exceeds 85%), then the second surface may be optically polished to reduce the transmittance to within desired bounds. Similarly, if too few scattering particles have been used to dope the optical plate (e.g., such that transmittance falls below 60%), then the second surface may be roughened to increase the transmittance to within desired bounds.

Of course, it is possible to leave the first and/or second surfaces unpolished and/or unroughened. The term “surface roughness Ra” is a widely used parameter in the art, and refers to the arithmetic average roughness.

Figure 5 provides a cross-sectional view of a portion of an optical plate 100, to more clearly demonstrate the shape/structure of the optical plate, particularly the microstructure arrangement 111.

It is possible to define a thickness t of the optical plate 100, being a distance between the first 110 and second 120 surfaces, particularly from a peak or apex 505 of a polygonal pyramid 111 A of the first surface 110 to the second surface 120.

Preferably, the thickness t of the optical plate 100 is between 0.5mm and 2mm. This provides a light, compact and materially efficient optical plate for use with lighting devices. With reference to Figure 1, such an optical plate can be readily supported by a supporting element with a thickness of between 0.5mm and 2mm.

In particular, the thickness t of the optical plate may be between 0.6mm and 1.7mm. This enhances the above-identified advantages.

Preferably, a height h_p of each polygonal pyramid 111A is between 16% and 42% (e.g., between 20% and 40%) of the thickness t of the optical plate 110. The height h_p is a distance from the peak or apex 505 of the polygonal pyramid 111A to the base 506 of the polygonal pyramid.

As an example, the height of each polygonal pyramid may be between 0.1mm and 0.5mm.

The pitch p (i.e. the peak-to-peak distance) between polygonal pyramids 111 A may be between 0.5mm to 1mm. Smaller pitches p would result in a very thin optical plate 100, which may be too brittle/delicate for long-term use of the optical plate 100 and lighting device. Longer pitches p may result in the polygonal pyramids becoming too visible to an enduser.

It has previously been explained how the present invention proposes to control a transmittance through an optical plate 100 to achieve a balance between glare reduction and light uniformity. In particular, an optical plate 100 having the proposed structure and a transmittance in the region of 65%-85% will achieve a good compromise between glare and light uniformity.

Figure 6 illustrates the relationship between transmittance T and change in glare AG. The transmittance T is measured as a percentage (%), using an established approach (such as those previously described). The change in glare AG is a change in glare from a device having an identical structure with a transmittance of 53%. For Figure 6, the glare is a normalized luminous intensity (measured in cd/klm) at a viewing angle of 75° to the optical plate. As most of glare is the light from viewing angle above 45°, the bigger the normalized luminous intensity at 75° degrees, the greater the glare. This therefore represents an appropriate measure for glare.

For the purposes of Figure 6, the optical plate comprises a polypropylene material doped with scattering particles.

From Figure 6, it can be clearly identified that increased transmittance leads to reduced glare.

However, it is also recognized that increased transmittance leads to reduced uniformity of light. A first group 610 of points on the graph demonstrate transmittances associated with a preferred uniformity of light. A second group 620 of points on the graph demonstrate transmittances with a less preferred uniformity of light.

Uniformity can be measured, for instance by detecting luminance (L) at a plurality of different points on the first surface 110. The closer the value of "Lmin /Lav", or "Lmin / Lmax" to 1, the higher uniformity it is. Lmin is the minimum detected luminance in aforementioned procedure. Lmin is the maximum detected luminance in said procedure. L_av is the average detected luminaire in the aforementioned procedure.

As can be seen from Figure 6, a preferred uniformity of light can still be achieved with reduced glare for transmittances in the region of 65%-81 %.

It is important to point out that whilst the second group 620 of points demonstrate a less preferred uniformity of light, such embodiments (e.g., optical plates having a transmittance in the region of from 81% to 85%) still provide sufficiently good uniformity of light for many commercial purposes.

For improved performance and to achieve preferred uniformity, it is preferable to avoid transmittances in the second group 620 of points, e.g., have a transmittance of between 65%-81%.

For even more improved performance, the transmittance is preferably between 70% and 81%. For yet more improved performance, the transmittance is preferably between 75% and 81%, or even more preferably between 77% and 81%. These approaches achieve greater reduction in glare without providing a less preferred uniformity of light.

For providing an improved safety margin for avoiding non-preferred uniformity of light, the transmittance is preferably from 65%-78%. For even more improved performance, the transmittance is preferably between 70% and 78%. For yet more improved performance, the transmittance is preferably between 75% and 78%. These approaches achieve greater reduction in glare without providing a less preferred uniformity of light.

In a preferable example, the transmittance is 77% (e.g., ±0.5) or 78% (e.g., ±0.5). In this approach, the light transmitted through the optical plate will have good uniformity and less glare.

It will be appreciate that these values are particularly advantageous when the optical plate comprises a polypropylene material that is doped (with scattering particles) to achieve the desired transmittance. Other materials may have other desired transmittance properties, as the relationship between transmittance and glare may differ for different types of material.

For instance, if the optical plate comprises a polycarbonate material that that is doped (with scattering particles) to achieve the desired transmittance, then a preferred transmittance is in the region of 65% to 71%. This achieves a similar effect to the optical plate used to produce the graph of Figure 6 when having a transmittance of between 77% to 81%.

Turning back to Figure 5, another recognition of the present invention is that the apex angle 0i of each polygonal pyramid 111 A also has an effect on glare. In the context of the present disclosure, the apex angle 0i is the angle between any two (e.g., opposing or facing) pyramid sides 510, 520 at the apex 505 of the pyramid 111A. The apex 505 is a point of the pyramid most distant from the second surface 120.

Figure 7 illustrates the effect of different apex angles 0i on the glare of light passing through an optical plate. The x-axis represents different apex angles 0i (measured in degrees °) and the y-axis represents a unified glare rating (UGR) measured using the approach set out by the International Commission on Illumination in the report/publication CIE 190:2010.

As can be clearly identified, an increase to the apex angle 0i causes a reduced glare.

Accordingly, it is preferable if the apex angle is greater than 100°, and even more preferably to be greater than 110°.

In some examples, the apex angle is no greater than 120°. Greater values, i.e., above 120°, for the apex angle exhibit reduced glare suppression.

The affect of apex angle on the unified glare rating UGR is relatively small. For instance, a change in apex angle from 100° to 120° in experiment conditions has shown a change in UGR of less than 0.5. However, it will still be appreciated that controlling or defining the apex angle allows for optimization of the glare reduction. It is also recognized that there is a causal relationship between apex angle and transmittance. In particular, the greater the apex angle, the greater the transmittance. This, by itself, would cause increased apex angles to result in reduced glare (via increasing the transmittance). Put another way, as increasing the apex angle 0i will increase the transmittance of the optical plate (and there is a herein established relationship between increase transmittance and reduce glare), so increasing the apex angle 0i will decrease the glare of the optical plate.

Nonetheless, even taking this effect into account, experimental analysis has shown that there is a relationship between increased apex angle and reduced glare that is not attributable to the natural increase in transmittance alone.

Thus, an amount of glare is dependent upon both the apex angle of the polygonal structures and the transmittance of the optical plate. The effect of transmittance is greater, but the effect of the apex angle(s) is not negligible.

The combined optical characteristics of uniformity and preventing glare with respect to the transmittance of the optical plate are illustrated in Figure 8.

The uniformity is measured in the same way as in Figure 6. As shown in Figure 8, the uniformity monotonically decreases when the transmittance increases. It’s determined that 70% is a threshold of acceptable uniformity, thus it can be concluded that the transmittance being equal or less than 72% is the acceptance range if considering uniformity performance only.

The preventing glare performance is measured with respect to a standard downlight of prior art. The test configuration is set up as shown in Figure 9. y = 0° is the direction of vertical downwards from the light source 12, and such direction aligns with the main optical axis of the light source. The measurement is taken in a C-plane passing this optical axis for the luminous intensity (normalization, cd/klm) at various y angles, and about various C-plane angles (for example, 0° - 90° - 180° - 270°). For testing of glare preventing performance, 175 is measured at y = 75°. The glare preventing performance:

wherein I75_sampie is the test result of a sample lighting device with the optical plate according to present invention, I75_standard is the test result of a prior art product without the optical plate of present invention.

As shown in Figure 8, the glare preventing performance monotonically increases when the transmittance increases. It’s determined that 15% is a threshold of acceptable glare preventing performance (the higher the better), thus it can be concluded that the transmittance being equal or more than 67% is the acceptance range if considering uniformity performance only.

Considering both the optical performances of uniformity and glare preventing, the overlapping range of 67% - 72% of transmittance of the optical plate is the optimal range.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. 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.

If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An optical plate (100) comprising: a micro-structure arrangement (111) formed of a plurality of polygonal pyramids; a first surface (110); and an opposite second surface (120, 420), wherein: the first surface is defined by the micro-structure arrangement; the second surface is planar; and the optical plate comprises a polymer material doped with scattering particles, such that the transmittance of the optical plate is in the range of 67% to 72%.

2. The optical plate according to claim 1, wherein the surface roughness Ra of the first surface (110) is less than or equal to 0.063pm.

3. The optical plate according to claim 1 or 2, wherein the surface roughness Ra of the second surface (120) is less than or equal to 0.063 pm.

4. The optical plate according to claim 1 or 2, wherein the second surface (420) is textured to have a surface roughness Ra of between 0.08pm and 3.2pm.

5. The optical plate according to any of claims 1 to 4, wherein a thickness (t) of the optical plate is between 0.5mm and 2mm.

6. The optical plate according to claim 5, wherein the thickness (t) of the optical plate is between 0.6mm and 1.7mm.

7. The optical plate according to any of claims 1 to 6, wherein the height (h_p) of each polygonal pyramid is between 16% and 42% of the thickness (t) of the optical plate.

8. The optical plate according to any of claims 1 to 7, wherein the height of each polygonal pyramid is between 0.1mm and 0.5mm.

9. The optical plate of any of claims 1 to 8, wherein the optical plate comprises a polymer material doped with scattering particles such that the transmittance of the optical plate is in the range of 65% to 81%.

10. The optical plate of claim 9, wherein the optical plate comprises a: a polycarbonate material doped with scattering particles or a polypropylene material doped with scattering particles .

11. The optical plate of any of claims 1 to 10, wherein: each polygonal pyramid is formed of a plurality of pyramid sides (510, 520) that meet at an apex; and for each polygonal pyramid, the angle 0i between any two pyramid sides at the apex is no less than 100°.

12. The optical plate of claim 11, wherein, for each polygonal pyramid, the angle between any two pyramid sides at the apex is no less than 110°.

13. A lighting device (10), comprising a housing (11), a light source (12), an electronic board (13), and an optical plate (100) according to any one of claims 1 to 12, wherein the optical plate is mounted on a light exit window (14) of the housing and over the light source.

14. The lighting device of claim 13, wherein a distance between the light source and the optical plate is between 25mm and 35mm.

15. The lighting device of claim 13 or 14 formed as a downlight.