WO2012146524A2

WO2012146524A2 - Led lamp

Info

Publication number: WO2012146524A2
Application number: PCT/EP2012/057149
Authority: WO
Inventors: Istvan Bakk
Original assignee: Tridonic Jennersdorf Gmbh
Priority date: 2011-04-29
Filing date: 2012-04-19
Publication date: 2012-11-01
Also published as: DE102011084945A1; WO2012146524A3

Abstract

The invention is directed to an LED lamp comprising a tubular translucent housing (2), and a linear light engine (3) having a linear heat sink (4, 40) and at least one LED module (5) being arranged on the heat sink (4, 40). The linear light engine (3) is arranged inside and enclosed by the housing (2) such that the linear light engine (3) is distanced from the inner wall of the housing (2) about its circumference in sectional side view, wherein the linear light engine (3) is distanced from the inner wall of the housing (2) by a predefined minimum distance (d) of at least 3mm in a horizontal direction (H) and angles (α, β, γ, δ) of at least +/- 45°, preferably +/- 60°, more preferably +/- 75°, most preferably +/- 90° from the horizontal direction (H) to allow the generation of an air circulation around the linear light engine (3) for enhanced heat transfer from the heat sink (4, 40) to the housing (2) by convection.

Description

LED lamp

The invention relates to an LED lamp comprising a tubular translucent housing and a linear light engine having a linear heat sink and at least one LED module being arranged on the heat sink, and particularly to a (linear) fluorescence retrofit LED lamp.

An LED lamp can be designed such that it can replace a conventional filament lamp, halogen lamp, fluorescence lamp or other type of conventional lamp. That is to say that the appearance of the LED lamp substantially matches the appearance of a

conventional filament, halogen, fluorescence or other conventional lamp and/or the LED lamp is provided with a plug connector for electrically and mechanically connecting the LED lamp with a conventional lamp socket of a corresponding conventional lamp. Such a lamp is generally denoted as "Retrofit LED lamp". A retrofit LED lamp having the appearance of a fluorescence lamp can thus be denominated as "fluorescence retrofit LED lamp".

Linear fluorescence retrofit LED lamps are known in the prior art. The current solutions of linear fluorescence LED lamps are based on light engines which are placed onto the inner wall of a tubular (glass) housing thus being in contact with the walls and preventing a sufficient air circulation or preventing an air circulation at all. Hence, the heat cannot be satisfactorily distributed, i.e. transferred to the walls of the housing.

It is thus an object of the invention to provide an LED module having a linear light engine in a tubular housing such that a satisfactory air circulation for an enhanced convection and heat transfer can be attained.

The object is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the present invention.

The invention is directed to an LED lamp comprising a tubular translucent housing or envelope, and a linear light engine having a linear heat sink and at least one LED module being arranged on the heat sink. The linear light engine is arranged inside and enclosed by the housing such that the linear light engine is distanced from the inner wall of the housing about its circumference in sectional side view, wherein the linear light engine is distanced from the inner wall of the housing by a predefined minimum distance of at least 3mm in a horizontal direction and angles of at least +/- 45°, preferably +/- 60°, more preferably +/- 75°, most preferably +/- 90° from the horizontal direction to allow the generation of an air circulation around the linear light engine for enhanced heat transfer from the heat sink to the housing by convection. As the light engine is kept substantially distanced from the inner wall of the tubular housing about its circumference, at least in the predefined angle range, an air circulation around the whole light engine is enabled and can also reach or pass the whole inner surface walls of the tubular housing. Due to the unimpeded air circulation the convection can be enhanced such that the heat of the LED module and heat sink can be satisfactorily, preferably substantially uniformly transferred to the walls of the housing. The heat is thus transferred from the heat sink to the housing mainly by convection.

The inner diameter of the housing can at least be 9mm and having a predefined minimum distance of at least 3mm, wherein the predefined minimum distance preferably is at least 3mm for a housing having an inner diameter of 12- 16mm, at least 5mm for a housing having an inner diameter of 22, 5 -26mm, and at least 7mm for a housing having an inner diameter of 35-38, 5mm. The predefined minimum distance can at least be 3mm for at least 75% of the inner surface of the housing according to the longitudinal direction of the housing, more preferably at least 90%, most preferably at least 95%, preferably except for the ends of the housing. Hence, convection as well as a sufficient heat transfer is securely enabled. Further, the convection from light engine to envelope is enhanced by the particular geometry of the housing. When seen in a cross-sectional view orthogonal to the longitudinal axis of the LED lamp, i.e. in a sectional side view, the heat sink has a flat surface onto which the LED module is mounted, and wherein the heat sink has an elongated portion extending from the rear side of the LED module or flat surface to promote airflow toward the housing. Preferably, the elongated portion or at least the distant end of the elongated portion of the heat sink extending from the rear side of the LED module or flat surface is narrower than the flat surface. More preferably, the elongated portion or at least the distant end of the elongated portion of the heat sink extending from the rear side of the LED module or flat surface tapers. By means of the respective designs and geometry of the heat sink, thermo conduction of the heat sink can be enhanced while at the same time allowing an enhanced heat transfer and convection from the light engine to the housing due to a directed air flow. In case of a tapered heat sink, the air stream of the heated air for convection can be even better guided along the tapered end of the heat sink for enhancing the air circulation and thus the convection.

Further, in a preferred embodiment when seen in a cross-sectional view orthogonal to the longitudinal axis of the LED lamp, i.e. in a sectional side view, the heat sink can also have a substantially triangular shape or form at least at its distant end wherein the elongated portion, i.e. the sides of said triangular heat sink extending away from the rear side of the LED module or flat surface for mounting the LED module, can be preferably formed concave and/or convex or better can be preferably formed by at least partially convex and/or concave and/or partially curved portions. By means of the before-mentioned triangular and preferably convex and/or concave design of the heat sink, the surface of the heat sink can be increased and thus the thermal conduction can be enhanced. Due to the triangular tapered form of the heat sink, the air stream of the heated air for air circulation can be guided in a predetermined manner and thus convection can be increased.

Preferably, when seen in a cross-sectional view orthogonal to the longitudinal axis of the LED lamp, i.e. in a sectional side view, the heat sink has a semicircular or circular form or shape or the elongated portion having a shape with rounded edges, wherein in case of a semi-circular form or shape the LED module is mounted on the given flat surface of the heat sink.

In a preferred embodiment, both ends of the tubular housing are covered by caps, wherein the linear light engine extends between said caps and is held by said caps to be distanced from the housing. As the light engine is mechanically fixed by the ends, i.e. by the end caps of the housing, it is easy to arrange the linear light engine preferably coaxially with respect to the tubular housing such that the light engine is distanced from the inner wall of the housing about its circumference by the pre-defined minimum distance. The caps can be made of a material having a good heat conduction, and may further comprise electrical connectors for electrically connecting the light engine with a corresponding lamp socket of a luminaire.

Preferably, the housing may have optical properties, the housing preferably being a diffusive or non-diffusive lens, and/or being at least partially covered with a reflective coating, and/or having a diffuser coating or a diffuser element connected to the inner or outer surface of the housing. Hence, the LED lamp can be easily provided with an optical means while the surface of the housing is not affected mechanically (e.g. scratched) by the inserted light engine due to the predefined minimum gap. The housing can also be made of glass or plastic, preferably a polymer or polymer compositions, wherein the material of the housing is translucent, preferably

transparent, and wherein the material of the housing or part(s) of the housing preferably has diffusive properties, e.g. is made of frosted glass or is patterned or coated .

The LED lamp may further comprise an optical element for at least one of the LED modules which is attached to or embedded in the heat sink or attached to or mounted on (e.g. by a plug-in method or the like) the LED module of the light engine to be arranged at least partially over the LED dice or SMD LEDs of the LED module and in the emitting direction of the LED module. The optical element preferably is a lens and/or at least partially a reflector or covered by a reflective material, and/or having diffusive properties. The optical element is preferably spanned over the LED module(s), wherein the spanned optical element preferably has a semi-circular cross- section, and wherein the optical element is preferably arranged such that it forms a gap between the optical element and the globe top of the LED dice or SMD LED of the LED module or between the optical element (9) and at least one LED die or SMD LED of the LED module (5). Said optical element can be a linear element arranged over the at least one LED module, preferably all LED modules, and extending along the longitudinal axis of the light engine. By means of such an optical element it is easy to provide light affecting elements for one, a plurality, or all of the LED modules to enhance the light distribution. Preferably, a color conversion material can be provided directly on the LED die or

SMD LED, and/or in a (silicone) globe top of the LED dice or SMD LEDs of the LED module, and/or on the optical element, and/or in the material of the optical element, and/or on the inner and/or outer surface of the housing and/or in the material of the housing for enhancing light distribution and particularly carrying out color conversion.

Preferably, a reflector can be placed around the LED module, preferably incorporated or integrally formed with the heat sink. Hence, the light distribution can be enhanced in an easy way. The at least one LED module or the LED dice or the SMD LEDs on the LED module can be arranged on the heat sink in at least one row and preferably connected in series and/or in parallel, wherein the rows can be mounted in a way to have a radial distribution of emitted light having 1, 2, 3, 4 or more axes.

According to a preferred embodiment of the invention, the LED lamp is a fluorescent retrofit LED lamp, preferably a linear fluorescent retrofit LED lamp. The LED lamp can also be a rectangular or cylindrical or tubular fluorescent retrofit LED lamp (e.g 2D tubular fluorescent lamp).

Further features, advantages and objects of the present invention will become apparent for a skilled person when reading the following detailed description of the

embodiments of the present invention when taking in conjunction with the figures of the enclosed drawings.

Figure 1 shows a perspective view of an LED lamp according to the invention

having a heat sink according to a first embodiment,

Figure 2 shows a perspective view of the LED lamp according to fig. 1 being cut along the line II-II, Figure 3 shows a cross-sectional view of the LED lamp according to fig. 1 being cut along the line II-II,

Figure 4 shows a second embodiment of a heat sink, Figure 5 shows the heat distribution of a cylindrical heat source in a tube.

Figure 1 shows an LED lamp 1 according to the invention. The LED lamp 1 comprises a tubular translucent housing 2. The housing 2 can be made of glass or plastic

(polymer or polymer compositions) or any other known material being used for corresponding lamp arrangements. The housing 2 is translucent, preferably transparent, and the material of the housing 2 or part(s) of the housing 2 can be clear, frosted, patterned or coated, thus the housing 2 preferably has diffusive properties. Preferably, the housing 2 has optical properties, that is the housing 2 can be a diffusive or non- diffusive lens, and/or can be at least partially covered with a reflective coating, and/or can have a diffuser coating or a diffuser element connected to the inner or outer surface of the housing 2. Color conversion materials and/or scattering materials can be provided in the material of the housing 2 or the inner and/or outer wall of the housing

2 can be covered by a color conversion material and/or a scattering material.

It has been mentioned that the housing 2 has a tubular form. In figure 1, the housing 2 has a circular cross-section. However, the invention is not limited to a circular cross- section but can have any possible cross-sectional form which can also change along its longitudinal axis L. For instance, the housing 2 can have a circular, square, rectangular, triangular or other form, which can also change by its dimension or form over the longitudinal axis L of the LED lamp 1 or housing 2. In case of a tubular cross- section of the housing 2, the housing 2 can preferably have diameters of 9mm, 12- 16mm, 22,5-26mm or 35-38, 5mm, but is not limited to said dimensions.

Now also referring to figures 2 and 3, the LED lamp 1 also comprises a linear light engine 3. The linear light engine 3 comprises a linear heat sink 4 which preferably extends along the tubular housing 2 in its longitudinal axis direction. The linear engine

3 further comprises at least one LED module 5 being arranged on the heat sink 4. The invention, however, is not limited to a particular number of LED modules 5 being arranged on the heat sink 4. There can also be arranged a plurality of LED modules 5 having at least one or a plurality of LED dice or SMD LEDs (not shown). The invention is further not limited to a particular arrangement or distribution of the LED modules 5 on the heat sink 4. The at least one LED module 5, the LED dice or the SMD LEDs on the LED module 5 are preferably arranged on the heat sink 4 in at least one row and preferably connected in series and/or in parallel, wherein the rows can be mounted in a way to have a radial distribution of emitted light having 1, 2, 3, 4 or more axes.

The LED module 5 may comprise a support or substrate or circuit board (PCB) 6 onto which at least one LED die or Surface-Mounted-Device (SMD) is provided. The LED module 5 may be a COB (Chip-on Board) module. The LED dice may be provided with a common globe top 7 or individual globe-tops 7 being dispensed or injected onto the dice. The globe top 7 preferably comprises a silicone material (silicone polymer(s) or their mixtures with another polymer(s)). The invention, however, is not limited to the number and arrangement of LED dice on the PCB 6 and/or under a particular globe top 7. As already mentioned, the LED dice of the LED module 5 are preferably connected in series and/or in parallel. The globe top 7 of the LED module 5 can comprise a color conversion material such that any desired color, color temperature or color tone can be emitted by each LED modules 5, wherein the LED modules 5 or LED dice/SMDs can emit light with the same or different colors, color temperatures or color tones as desired. For emitting white light, a blue or UVLED die can be used in combination with green, greenish-yellow, yellow or red light emitting phosphors (e.g. garnets, orthosilicates, nitrides and/or SiAlONs) or their mixtures preferably being provided in the globe top 7. A fraction of the blue light thus undergoes the Stokes-shift being transformed from shorter wavelengths to longer. The mixture of the emitted light and the converted light is white light being emitted from the LED module 5. By means of scattering material, which can be provided in the globe top 7 or on or in the housing 2 or on or in the optical element 9, the color mixing can be enhanced to emit a homogeneous white light. In one embodiment of the invention a green, greenish- yellow, yellow or red phosphor(s) is incorporated into the globe-top(s) 7 and a further green, greenish-yellow, yellow or red phosphor or a mixture comprising at least one of said phosphors is incorporated in/on the optical element 9 and/or in/on the housing 2. Preferably, a green, greenish-yellow, yellow phosphor (e.g an orthosilicate (BOSE)) and a red phosphor (e.g. a nitride) are included in the globe-top(s) 7 and a further green, greenish-yellow, yellow phosphor (e.g. a garnet) is provided in the optical element 9 or in the housing 2. Alternatively, the red phosphor in the globe-top(s) may be substituted by a red LED die or SMD. In a further embodiment a green, greenish- yellow, yellow phosphor (e.g an orthosilicate (BOSE)) is included in the globe-top(s) 7 and mixture of a further green, greenish-yellow, yellow phosphor (e.g. a garnet) and a red phosphor (e.g. a nitride) is provided in the optical element 9 or in the housing 2. In another embodiment of the invention no phosphors are provided in the globe top(s) 7, but a red phosphor (e.g. a nitride) is incorporated into or on the optical element 9 and a green, greenish-yellow or yellow phosphor(s) is provided in/on the housing 2.

However, the invention is not limited to the before-mentioned embodiments.

The heat sink 4 can have any particular cross-sectional form. Preferably, when seen in a cross-sectional view orthogonal to the longitudinal axis L of the LED lamp 1, i.e. in a sectional side view, the heat sink 4 has a flat surface 20 onto which the LED module 5 is mounted or attached, and the heat sink 4 further has an elongated portion 30 extending from the rear side of the LED module 5 or flat surface 20 to promote airflow toward the housing 2. In case the heat sink 4 comprises such an elongated portion 30, the LED lamp 1 is preferably used in an orientation as shown in figure 2 to efficiently promote the air flow by being directed with the aid of the elongated portion 30. The elongated portion 30 or at least the distant end 31 of the elongated portion 30 of the heat sink 4 extends from the rear side of the LED module 5 or flat surface 20 preferably having narrower cross-section than the flat surface 20. More preferably, the elongated portion 30 or at least the distant end 31 of the elongated portion 30 of the heat sink 4 extending from the rear side of the LED module 5 or flat surface 20 tapers as shown in figures 1 to 3. Thus, the air flow can be enhanced as being directed to allow convection and thus heat transfer from the light engine 3 to the housing 2.

Preferably, when seen in a cross-sectional view orthogonal to the longitudinal axis L of the LED lamp 1, i.e. in a sectional side view, the heat sink 4 has a substantially triangular shape at least at its distant end 31. More preferably, the sides of the triangular heat sink extending away from the LED module 5 are formed convex or concave thus increasing the surface of the heat sink 4. Such a triangular cross-sectional form is shown in figures 1-3, wherein the sides of the triangular heat sink 4 extending away from the LED module 5 have a concave form over the whole length.

Alternatively or additionally, the border line(s) of the heat sink 4 may be at least partially curved.

Alternatively, when seen in a cross-sectional view orthogonal to the longitudinal axis L of the LED lamp 1, i.e. in a sectional side view, the heat sink 4 can have a semicircular or circular shape (not shown in the figures) or the elongated portion having a shape with rounded edges (see, for instance, the heat sink 40 in figure 4 described later). In case the heat sink 4 has a semi-circular shape, the LED module 5 is mounted (e.g by a plug-in method) or attached on the given flat surface thereof. In case of a cylindrical heat sink, the PCB or a support 6 of the LED module 5 forms the flat surface or an additional member having a flat surface is attached. With respect to figures 1-3, the heat sink 4 can be made of a solid material, or can be hollow as shown in figure 4. In figure 4, the heat sink 40 also has a substantially triangular base formed by the substantially flat surface, and extending sides 43, 44. The LED module can be placed on the substantially flat surface 41 as similarly shown in figure 2. The distant end 42 extending from the back of the LED module 5 (or the flat surface 41) tapers. The extending sides 43, 44 of said substantially triangular heat sink 40 are formed convex at a proximal end 45. It is noted again that the design of the heat sink is not limited to the preferred embodiments as long as the heat sink 4, 40 does not get in touch with the housing 2 preferably over its total length when being arranged inside the housing 2 for use of the LED lamp 1 as will be described next. The designs of the shown embodiments, however, provide a preferred form/design of the heat sink 4, 40 for providing a good air/gas circulation in the housing 2 for an enhanced convection and thus an enhanced heat transfer from the heat sink 4, 40 to the housing 2. In this regard, when seen in a cross-sectional view orthogonal to the longitudinal axis L of the LED lamp 1, the heat sink 4, 40 preferably has a

substantially triangular shape at least at its distant end 42, wherein the sides 43, 44 of the triangular heat sink 4, 40 extending away from the rear side of the LED module 5 or the flat surface 41 for mounting the LED module 5 are preferably formed by at least partially convex and/or concave and/or partially curved portions.

The heat sink 4, 40 can comprise a metal (e.g. Al) or a polymer, especially a heat conductive polymer. The heat conductivity of applied heat sink materials can be >0.5 W/mK, preferably≥8W/mK, more preferably≥ 150W/mK.

It is possible that the substrate 6 is an Insulated Metal Substrate (IMS) which can be attached/mounted on the heat sink 3 or which can alternatively or additionally form the heat sink 3 according to the invention thus reducing the number of parts.

With respect to figures 1-3, particularly figure 3, the linear light engine 3 is arranged inside and enclosed by the housing 2 such that the linear light engine 3 is distanced from the inner wall of the housing 2 about its circumference in sectional side view, wherein the linear light engine 3 is distanced from the inner wall of the housing 2 by a pre-defined minimum distance d of at least 3mm in a horizontal direction H and angles α, β, γ, and δ of at least +/- 45°, preferably +/- 60°, more preferably +/- 75°, most preferably +/- 90° from the horizontal direction H to allow the generation of an air circulation around the linear light engine for enhanced heat transfer from the heat sink 4, 40 to the housing 2 by convection.

It has been defined, that the predefined minimum distance d should be 3mm or more. In particular, to provide a good convection for an improved heat transfer from the light engine 3 to the housing 2, the minimum distance d of the air gap between the light engine 3 and the housing 2 (at least along the particular angel ranges) is also dependent on the inner diameter D of the housing 2 (in case of a circular housing 2). In case of an inner diameter D of the housing 2 of 9mm the predefined minimum distance d is at least 2mm, preferably at least 3mm, wherein the predefined minimum distance d preferably is at least 3mm for a housing 2 having an inner diameter D of 12- 16mm, at least 5mm for a housing 2 having an inner diameter D of 22,5-26mm, and at least 7mm for a housing 2 having an inner diameter D of 35 -38, 5mm. To further enhance the convection, the predefined minimum distance d should be at least 3mm for at least 75% of the inner surface of the housing 2 according to the longitudinal direction of the housing 2, more preferably at least 90%, most preferably at least 95%. These specific values are preferably not applied for the ends of the housing 2, where the light engine 3 is fixed as it will be described in the following.

For inserting the light engine 3 inside the housing 2, at least one or both sides/ends of the housing 2 are open. Preferably, both ends of the tubular housing 2 are covered by caps 8, wherein the linear light engine 3 extends between said caps 8 and is held (i.e. mechanically fixed) by said caps 8 to be distanced from the housing 2 as can be clearly seen in figures 1-3. Preferably, the caps 8 comprise electrical connectors (not shown) for electrically connecting the light engine 3 (i.e. the LED lame 1) with a

corresponding lamp socket of a luminaire. As the caps 8 are in contact with the light engine, the can be made of a material having a good thermal heat conduction to transfer the heat to the housing 2 or radiate the heat to the atmosphere.

The caps 8 can comprise extensions (not shown) substantially having the form of the outer contour of the light engine 3 in its cross-sectional view. The caps 8 can thus be simply imposed on the light engine 3 with the matching extensions for securely holding the light engine 3. The invention is not limited to such a holding means, but the light engine 3 and caps 8 can also comprise other known interrelated holding means like a screw joint, a bayonet joint, a clip or the like. The light engine 3 does also not necessarily be held by the end caps 8. There can also be provided holding means inside the housing 2 and preferably close to the (open) end portions. These holding means can be attached to the housing 2 such that the light engine 3 is held inside the housing 2 in a distanced manner to the inner walls thereof and such that air circulation is not hindered by said holding means. Further, it is also possible to arrange two or more linear light engines 3 in a liner housing 2, which light engines can then be connected by any known mechanical and electrical connecting (and holding) means.

By arranging the light engine distanced from the housing 2 an air circulation is enabled due to the substantial distances of the light engine 3 from the walls of the housing 2 thus enhancing convection such that the heat of the light engine 3 is satisfactorily transferred to the walls of the housing 2. In a preferred embodiment, the light engine 3 is arranged inside the housing 2 such that the longitudinal axis L of the LED lamp 1 or housing 2 and the longitudinal axis E of the light engine 3 are coaxially arranged. The effect of the enhanced convection and air circulation is exemplarily shown in figure 5 showing the heat distribution of a cylindrical heat source 100 in a tube 200. It can be clearly seen that the arrangement of the heat source 100 being distanced from the walls of the tube 200 results in an enhanced air circulation thus resulting in an enhanced convection such that the heat can be satisfactorily transferred to the walls of the tube 200. The air circulation can be further enhanced by a particular geometry and design of the housing 2 and light engine 3, particularly the heat sink 4, 40 of which two embodiments are presented in the above description and figures 1-4. Optionally, the light engine 3 may further comprise an optical element 9. The optical element 9 can be a lens and/or can at least partially be a reflector, and/or having diffusive or color conversion properties. In the latter case, the optical element 9 may comprise color conversion materials and/or scattering materials being provided in the material of the optical element 9 or covering the optical element 9. Applicable phosphors as color conversion materials known in the state of art can be used such as garnets, silicates, orthosilicates, nitrides, SiAlONs etc.

The optical element 9 is attached to or embedded in the heat sink 4 or attached to or into, mounted on or into or plugged into the LED module 5 to be arranged at least partially over the LED dice or SMD LEDs of the LED module 5 and in the emitting direction of the LED module 5. The optical element 9 is at least provided for one of the LED modules 5. Preferably, the optical element 9 is a linear element as shown in figure 2, and arranged over the at least one, a plurality or all of the LED module(s) 5 and extending along the longitudinal axis E of the light engine 3. Preferably, the linear optical element 9 is spanned over the LED module(s) 5. In this case, a gap 10 is preferably formed between the optical element 9 and the globe top 7 of the LED dice or SMD LED of the LED module(s) 5 or between the optical element 9 and at least one LED die or SMD LED of the LED module 5. The optical element 9 can have a semicircular cross-sectional form. It is noted that the cross-sectional form of the optical element is, however, not limited to a semi-circular form but can have any desired form, as, for instance, a rectangular form or the like. The form and arrangement of the optical element 9 as well as its extension along the longitudinal direction are merely limited by the requirements of its desired optical properties. In a preferred embodiment, a reflector (not shown) is placed at least partially around the LED module 5. Preferably, the reflector is placed at least partially around the PCB 6 to enhance the light distribution and efficacy of the LED module 5. In a more preferred embodiment, the reflector is incorporated or integrally formed with the heat sink 4, 40. The heat sink 4, 40 can thus be made of aluminum or the like which also has a good thermal conduction. Alternatively, the heat sink 4, 40 can also be coated with a reflective coating material. As reflective material non-conductive or conductive substances like Ti0₂, BaTi0₃, Cr, A1₂0₃ can be applied.

With respect to figure 1 , the LED lamp 1 can be a linear luminescent retrofit LED lamp also having the respective electrical connectors (preferably arranged in the caps 8) to be arranged in a lamp socket of a corresponding luminaire. The LED lamp 1 as shown in figure 1 is a T8 30cm long construction. However, the invention is not limited to said particular construction but covers all possible LED lamps having a tubular housing enclosing a linear light engine according to the invention.

It is also possible to connect two or more of the inventive LED lamps in a linear, i.e. straight (180°), or angled (< 180°) manner. In this case, the caps 8 can also be used as connection means for connecting two housings 2 and holding the light engine 3 of both of the respective housings 2. In case of an angled arrangement, the caps 8 can be bent to a desired angle such that adjacent LED lamps 1 have an angle of less than 180°. It is noted that the invention is not limited to the embodiments as long as being covered by the following claims. In particular, the invention is not limited to any size, form, dimension, number and/or material of the housing 2, the light engine 3, the heat sink 4, the LED module 5 (including dice, PCB 6, and globe top 7), the caps 8, the optical element 9, the reflector as well as the color conversion materials or scattering materials. Further, color conversion materials (phosphors) can be provided directly on the LED die or SMD LED, and/or in a (silicone) globe top 7 of the LED dice or SMD LEDs of the LED module 5, and/or on the optical element 9, and/or in the material of the optical element 9, and/or on the surface of the housing 2, and/or in the material of the housing 2.

Claims

An LED lamp comprising:

a tubular translucent housing (2), and

a linear light engine (3) having a linear heat sink (4, 40) and at least one LED module (5) being arranged on the heat sink (4, 40),

characterized in that

the linear light engine (3) is arranged inside and enclosed by the housing (2) such that the linear light engine (3) is distanced from the inner wall of the housing (2) about its circumference in sectional side view, wherein the linear light engine (3) is distanced from the inner wall of the housing (2) by a predefined minimum distance (d) of at least 3mm in a horizontal direction (H) and angles (α, β, γ, δ) of at least +/- 45°, preferably +/- 60°, more preferably +/- 75°, most preferably +/- 90° from the horizontal direction (H) to allow the generation of an air circulation around the linear light engine (3) for enhanced heat transfer from the heat sink (4, 40) to the housing (2) by convection.

The LED lamp according to claim 1 , wherein the inner diameter of the housing (2) is at least 9mm, wherein the predefined minimum distance preferably is at least 3mm for a housing (2) having an inner diameter of 12- 16mm, at least 5mm for a housing (2) having an inner diameter of 22,5- 26mm, and at least 7mm for a housing (2) having an inner diameter of 35- 38,5mm.

The LED lamp according to claim 1 or 2, wherein the predefined minimum distance (d) is at least 3mm for at least 75% of the inner surface of the housing (2) according to the longitudinal direction of the housing (2), more preferably at least 90%, most preferably at least 95%, preferably except for the ends of the housing (2).

4. The LED lamp according to any of the preceding claims, wherein, when seen in a cross-sectional view orthogonal to the longitudinal axis (L) of the LED lamp (1), the heat sink (4, 40) has a flat surface (41) onto which the LED module (5) is mounted, and wherein the heat sink (4, 40) has an elongated portion extending from the rear side of the LED module (5) or flat surface (41) to promote airflow toward the housing (2), and

wherein the elongated portion or at least the distant end (42) of the elongated portion of the heat sink (4, 40) extending from the rear side of the LED module (5) or flat surface (41) preferably being narrower than the flat surface (41), more preferably tapers.

The LED lamp according to claim 4, wherein, when seen in a cross-sectional view orthogonal to the longitudinal axis (L) of the LED lamp (1), the heat sink (4, 40) has a substantially triangular shape at least at its distant end (42), wherein the sides (43, 44) of the triangular heat sink (4, 40) extending away from the rear side of the LED module (5) or the flat surface (41) for mounting the LED module (5) are preferably formed by at least partially convex and/or concave and/or partially curved portions.

The LED lamp according to claim 4, wherein, when seen in a cross-sectional view orthogonal to the longitudinal axis (L) of the LED lamp (1), the heat sink (4, 40) has a semicircular or circular shape or the elongated portion having a shape with rounded edges, wherein in case of a semi-circular shape the LED module (5) is mounted on the flat surface of the heat sink (4, 40).

The LED lamp according to any of the preceding claims, wherein both ends of the tubular housing (2) are covered by caps (8), wherein the linear light engine (3) extends between said caps (8) and is held by said caps (8) to be distanced from the housing (2), wherein the caps (8) fix mechanically the light engine (3), and wherein the caps (8) preferably comprise electrical connectors for electrically connecting the light engine (3) with a corresponding lamp socket of a luminaire.

The LED lamp according to any of the preceding claims, wherein the housing (2) has optical properties, the housing (2) preferably being a diffusive or non- diffusive lens, and/or being at least partially covered with a reflective coating, and/or having a diffuser coating or a diffuser element connected to the inner or outer surface of the housing (2).

The LED lamp according to any of the preceding claims, wherein the housing (2) is made of glass or plastic, preferably a polymer or polymer compositions, wherein the material of the housing is translucent, preferably transparent, and wherein the material of the housing (2) or part(s) of the housing (2) preferably has diffusive properties, e.g. made of frosted glass or being patterned or coated.

The LED lamp according to any of the preceding claims, wherein the light engine (3) further comprises an optical element (9) for at least one of the LED modules (5) and being attached to or embedded in the heat sink (4) or attached to the LED module (5) to be arranged at least partially over the LED dice or SMD LEDs of the LED module (5) and in the emitting direction of the LED module (5),

wherein the optical element (9) preferably being a lens and/or at least partially a reflector or covered by a reflective material, and/or having diffusive properties,

wherein the optical element (9) preferably being spanned over the LED modules (5),

wherein the optical element (9) preferably has a semi-circular cross-section, and

wherein the optical element (9) is arranged such that it preferably forms a gap (10) between the optical element (9) and a globe top (7) dispensed on at least one LED die; or SMD LED of the LED module (5) or between the optical element (9) and at least one LED die or SMD LED of the LED module (5).

The LED lamp according to claim 10, wherein the optical element (9) is a linear element arranged over the at least one LED module (5) and extending along the longitudinal axis (E) of the light engine (3),.

The LED lamp according to any of the preceding claims, wherein a color conversion material is provided directly on the LED die or SMD LEDs, and/or in a globe top (7) of the LED dice or SMD LEDs of the LED module (5), and/or on the optical element (9), and/or in the material of the optical element (9), and/or on the surface of the housing (2), and/or in the material of the housing (2).

13. The LED lamp according to any of the preceding claims, wherein a reflector is placed around the LED module (5), preferably incorporated or integrally formed with the heat sink (4, 40).

14. The LED lamp according to any of the preceding claims, wherein the at least one LED module (5) or the LED dice or the SMD LEDs on the LED module (5) are arranged on the heat sink (4, 40) in at least one row and preferably connected in series and/or in parallel, wherein the rows can be mounted in a way to have a radial distribution of emitted light having 1, 2, 3, 4 or more axes.

15. The LED lamp according to any of the preceding claims, wherein the LED lamp (1) is a fluorescent retrofit LED lamp, preferably a linear fluorescent retrofit LED lamp.