WO2011001329A1

WO2011001329A1 - Led luminaire using louvers as a heat sink

Info

Publication number: WO2011001329A1
Application number: PCT/IB2010/052841
Authority: WO
Inventors: Ramon Pascal Van Gorkom; Denis Joseph Carel Van Oers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-06-29
Filing date: 2010-06-23
Publication date: 2011-01-06
Also published as: TW201113467A

Abstract

An illumination system (10) comprising at least one light source (2), a heat sinking structure (5) on which the light source is arranged, said structure facilitating dissipation of heat from said light source and being at least partly light-transmissive and at least one reflector (3) arranged for reflecting light emitted by said light source, said reflector being arranged in the light emitting direction of the light source and configured to reflect incident light in a direction towards said heat sinking structure.

Description

LED LUMINAIRE USING LOUVERS AS A HEAT SINK

FIELD OF THE INVENTION

The present invention relates to an illumination system for emitting light, wherein a heat sinking structure is provided to dissipate heat emitted by a light source. BACKGROUND OF THE INVENTION

The use of artificial lighting to achieve practical or aesthetic effects is continuously increasing, and there are numerous examples of lighting and illumination systems for e.g. offices, restaurants, museums, advertising boards, homes, shops, shop windows, and so on. The purpose of lighting may be the creation of a general illumination or to focus the light on certain areas or objects.

Common to light sources such as light-emitting diodes (LEDs), light bulbs, lasers and lamps is that the sources emit heat, an effect which often is as unavoidable as it is unwanted. Thus, it is necessary to dissipate excess heat in order to maintain the reliability of the illumination system and to prevent premature failure of the light sources.

LEDs are continuously becoming cheaper and more efficient, having several advantages over other sources of light, such as a high reliability, a long lifetime and a high efficiency. However, lighting modules for use in a display or an illumination device often require many LEDs, and as most of the diodes are driven at the same time, the result is a quick rise in LED module temperature. Since general LED modules often do not have heat sinks with satisfactory heat dissipating efficiency, operations of general LED modules are often erratic and unstable because of the rapid build-up of heat. Consequently, the light from a LED module often flickers, causing degradation of the quality of the display or

illumination. Thus, the dissipation of heat emitted from the diodes is important, and a heat sink is often required to cool the LEDs to obtain an optimal operation temperature. However, a heat sink in connection to a LED module often requires considerable space. Although the heat sink size may be reduced by making use of active cooling such provided by means of e.g. fans, the disadvantages related to this solution are that the active cooling generally is more noisy, consumes more electrical power, is more susceptible to collect dust and runs a higher risk of breaking down due to mechanical wear compared to a system without an active cooling.

In patent document US 2005/0168994, a LED system is disclosed with a back- reflector to mirror light back in the direction of the light source. In this arrangement, active cooling is avoided by a supporting structure provided in front of the LEDs to conduct heat to a sink positioned on the opposite side of the reflector relative to the LEDs.

However, there are problems related to this arrangement. Firstly, the heat sink as disclosed is still bulky. This is problematic as the heat sink may have to be placed inside the ceiling, a solution which moreover suffers from poor convection within the ceiling.

Moreover, a large-scale luminaire placed in the ceiling is unwanted, especially for tall people, as the risk for injuries by colliding with the luminaire is increased.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved illumination system for solving the above discussed prior art problems.

According to a first aspect of the present invention, this is realized by an illumination system comprising at least one light source, a heat sinking structure on which the light source is arranged, said structure facilitating dissipation of heat from said light source and being at least partly light-transmissive, and at least one reflector arranged for reflecting light emitted by said light source, said reflector being arranged in the light emitting direction of the light source and configured to reflect incident light in a direction towards said heat sinking structure.

With this arrangement, the illumination system becomes smaller compared to prior art illumination systems, as prior art heat sinks positioned on top or at the periphery of the reflector leads to a bulky illumination system. Throughout the application, the terms

"illumination system" and "luminaire" are alternately used. A smaller luminaire has several advantages compared to larger luminaire installations. As an example, a smaller sized luminaire placed in the ceiling is desirable, especially in rooms where the ceilings are low, as the risk for injuries by persons colliding with the luminaire is decreased. Moreover, reduced size luminaires are easier to move, an effect which is often desired in e.g. office spaces, museums, and shops, where the light sources often need to be relocated. Further, a smaller luminaire may enhance the aesthetics of the environment where the luminaire is provided.

Additionally, with the reflector being arranged in the light emitting direction of the light source and configured to reflect incident light in a direction towards the heat sinking structure, the convection of the heat sink is improved compared to the realization of a heat sink positioned on top of the reflector. Moreover, by this invention, any placement of a heat sink within the ceiling may be avoided, where the heat convection often is poor.

Furthermore, the placing of a heat sink within the ceiling requires operation in the ceiling interior, the installation may be tedious, costly, and, possibly, also dangerous for the installer, whereas the illumination system of the present invention mitigates these, and more, aspects.

Furthermore, with the reflector being arranged in the light emitting direction of the light source and configured to reflect incident light in a direction towards the heat sinking structure, the cooling of the at least one light source is improved. Consider a prior art luminaire provided e.g. in the ceiling for the illumination of an area or an object or objects below the luminaire. As warm air rises upwards, in the direction of the heat sink, the luminaire deteriorates the cooling performance of the light source comprised in the luminaire. Thus, as compared to prior art luminaires, the inventive illumination system dissipates the heat more efficiently.

According to an embodiment of the present invention, the heat sinking structure provides optical guidance of the light emitted by the at least one light source. In other words, the heat sinking structure may direct the emitted light while acting as a heat sink for the dissipation of heat emitted from the light sources. Thus, the heat sinking structure is, in an embodiment of the invention, capable of both cooling the light sources and guiding the emitted light. The benefits of this arrangement are numerous; the size of the illumination system may be decreased. Moreover, the inventive illumination system provides a reduced- size luminaire without the use of active cooling provided by means of e.g. fans. The advantages related to this solution are, amongst others, that the omission of any active cooling provides a more silent, cheaper, easily cleanable and reliable system in operation. Moreover, higher costs related to the repair, maintenance and /or mounting of prior art heat sink arrangements may be avoided.

The term "heat sink" should, in this context, be construed as an object that transfers heat from a first object at a relatively high temperature to a second object at a lower temperature with a greater heat capacity, thereby lowering the temperature of the first object, fulfilling the role of the heat sink as a cooling device.

According to an embodiment of the present invention, the heat sinking structure substantially collimates the reflected light. By this, the heat sinking structure aligns the beam path from the light beams in a specific direction such that an increased illumination may be provided in a preferred area or areas, or to a specific object or objects, the heat sinking structure all the same providing heat sink properties for the dissipation of heat emitted from the light sources. As an example, it may be desired to concentrate light to an area or an object such as e.g. a board, a painting, a desk or the like to make the area more visible or to make possible that attention is drawn to that area. Subsequently, a decreased illumination may be provided in an area where illumination is not preferred. As an example, the collimation of light to an object or objects contributes to a darkening of the area not focused by the light, such that an observer in that area may more easily perceive the object or objects. Further, the heat sinking structure may guide the reflected light from the reflector such that glare is minimized. This effect of collimation of light to a preferred area is advantageous as glare may deteriorate the desired lighting e.g. in an office. As an example, a heat sinking structure provided perpendicular to an axis parallel to the long axis of an elongated luminaire may provide reduced glare along that long axis. By this, the light may be directed in a way such to avoid that persons become dazzled by the light provided by the luminaire.

By the term "collimated", it is here meant a beam of substantially parallel light rays, wherein collimation of light may be achieved by at least one aperture, defining the ray divergence.

According to aspect further embodiment of the present invention, the heat sinking structure may comprise louvers. A benefit of the louvers is that they define the light as emitted from the illumination system, further improving the guidance of light and hindering glare in the direction along the long axis of the luminaire, while providing a heat sinking effect for the cooling of the at least one light source. As an example, when the luminaire is used for illuminating an office space, whereby a luminaire may be mounted in the ceiling, mounted against the ceiling, or pending from the ceiling, the louvers may provide an appropriate distribution of the light intensity within the downwardly directed light, whereas at the same time, providing satisfactory heat sink properties to dissipate heat from the at least one light source. As a further example, the louvers may be rectangular-shaped, such that the louvers may be provided perpendicular to an axis parallel to the long axis of the louvers. Moreover, this arrangement of the heat sinking structure facilitates several aspects of the illumination system such as the construction, mounting and maintenance of the system. As an example, in the case that a luminaire with the described illumination system needs to be repaired due to any damaged louver or louvers, the damaged means may be independently replaced without the need to demount the luminaire. Consequently, the illumination system may still provide a satisfactory luminous and cooling functionality, even though one or several louvers have been damaged. Further, this embodiment ensures an inexpensive maintenance of the illumination system.

According to an exemplifying embodiment of the present invention, the heat sinking structure may comprise gratings, grilles, vanes, trellises, lattices or the like. These alternatives may further ameliorate the desired lighting for the luminaire and cooling for the at least one light source. As an example, a first desired illumination system may be constructed where there are high demands on the luminous intensity but low demands on the heat sinking effect. Analogously, another illumination system may be constructed where there are high demands on the cooling of the at least one light source provided by the heat sink effect, but low demands on the luminous intensity. These examples, and any other combination of desired properties regarding the cooling and optical functionality of the heat sinking structure, may be provided by the proposed embodiments as mentioned.

According to an embodiment of the present invention, the at least one light source is a light-emitting diode (LED). This may be advantageous as LEDs continuously are becoming cheaper and more efficient, having several advantages over other sources of light, including a high reliability, a long lifetime and a high efficiency. An illumination system of the present invention comprising a LED as a light source provides a particular improvement in that such an illumination system efficiently transfers heat away from the LED PN junction. If the generated thermal energy from the LEDs is high, cooling means may be required to maintain LED performance. Some applications feature numerous LED lights within a restrained space and cannot efficiently dissipate enough heat. However, with the disclosed invention, the heat sinking structure dissipates the excess heat from the LEDs in order to maintain operational reliability of the illumination system.

According to another embodiment of the invention, remote phosphor is arranged at the light-emitting diode for converting at least a part of the light emitted by the at least one light-emitting diode, such that the emitted light yields a backscattered

photo luminescence. One benefit of such an arrangement is that the LEDs degrade at a lower rate, thereby further contributing to the performance of the system of the disclosed invention. As an example, blue LEDs may be used, separated from the remote phosphor.

Furthermore, a remote phosphor system may be omitted, and instead, white

LEDs may be used. Alternatively, a red, green and blue LED may be combined to provide a white light output.

Additionally, any other color may be obtained by the use of any other color, or combination of colors, of the LEDs. By this, white or colored light may be emitted from the at least one light-emitting diode in the illumination system, providing a heat sink comprising heat sinking structure for the mentioned light.

According to one embodiment, the at least one light source in the illumination system is a laser, an incandescent light bulb, a discharge lamp, a fluorescent lamp or the like. The use of any, or variations, of the light sources mentioned within the illumination system disclosed may meet specific demands of e.g. luminous intensity, coherent and/or

monochromatic light, and so on. Therefore, by such a light source, the illumination system may provide a light that meets one or several of these demands while the functionalities regarding the cooling and the optical guidance provided by the heat sinking structure may further improve the luminaire performance.

According to another aspect of the present invention, the heat sinking structure is arranged to provide a temperature difference between an outer portion and an inner portion of the heat sinking structure, such that a temperature of the outer portion of the heat sinking structure is lower compared to a temperature of the inner portion of the heat sinking structure.

By this, the temperature difference between the outer and the inner portions of the heat sinking structure further increases the convection. This effect may be achieved by constructing the heat sinking structure from a suitable choice of material or materials. As an example, the outer portion may be formed by a first material and the inner portion may be formed by a second material, the second object having a greater heat capacity compared to the first object such that heat passes from the first to the second portion. Alternatively, the thicknesses of the heat sinking structure may be adapted to provide an increased convection. Further, the heat sinking structure may be split up into different parts with little or no thermal conduction.

According to an embodiment, the heat sinking structure is formed by a heat- conductive material, thereby efficiently transferring heat. By this, the size of the luminaire illumination system may be further reduced.

According to another embodiment of the invention, the heat sinking structure is formed by copper, aluminum or the like. As copper is a metal with a high thermal conductivity, with further advantages of e.g. providing compact, easily manufactured heat sinking structures, its use for providing a heat sinking structure is desirable. Likewise, having properties advantageous for the formation of a heat sink, aluminum may also be used for the heat sinking structure for the illumination system.

According to another embodiment of the invention, the heat sinking structure is coated with a layer arranged to absorb light with wavelengths in the infrared spectrum whilst reflecting light with wavelengths in the visible light spectrum. This embodiment ensures that a high portion of the heat, resulting from the infrared spectrum, is absorbed by the heat sink comprising the heat sinking structure whereas the visible light is reflected such as to provide a satisfactory lighting for the luminaire.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Persons skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Figure 1 shows a schematic view of a conventional illumination system.

Figure 2 shows a schematic view of the illumination system according to an exemplifying embodiment of the invention.

Figure 3 shows a perspective view of the illumination system according to an exemplifying embodiment of the invention.

Figures 4a-d show cross-sectional views of louvers according to exemplifying embodiments of the invention.

DETAILED DESCRIPTION

In the following description, the present invention is described with reference to a luminaire with an illumination system.

Referring to Fig. 1, there is shown a schematic view of a prior art luminaire 1 having a plurality of LEDs 2 (of which only one is shown) as light sources. Typically, the luminaire extends in the direction of the y axis, and comprises a plurality of LEDs arranged in the luminaire along said axis. A concave reflector 3 partially surrounds the plurality of LEDs 2, reflecting the light 4 emitted by the plurality of LEDs 2. The concave reflector 3 is positioned such that the plurality of LEDs 2 are positioned at the centre of the concave reflector 3. The concave reflector 3 substantially collimates the light 4 such as to hinder glare along the x axis, perpendicular to the elongated axis of the luminaire 1. A plurality of louvers 5 (of which only one is shown) are provided at least partly inside the concave reflector 3, in the light path between the concave reflector 3 and a periphery of the reflected light 6 to hinder glare along the y axis of the luminaire 1. The plurality of louvers 5 are rectangular- shaped with their long axis parallel to the x axis. A remote phosphor 7 is provided at the LEDs between the plurality of louvers 5 and the concave reflector 3, the remote phosphor 7 substantially surrounding the plurality of LEDs 2 such as to convert at least a part of the light 4 emitted by the plurality of LEDs 2. On top of the plurality of LEDs 2, on the back side of the concave reflector 3, a heat sink 8 for absorbing heat emitted from the plurality of LEDs 2 is positioned. The heat sink 8 is shaped as a rectangular parallelepiped, with its long axis elongated parallel to the y axis.

Referring now to Fig. 2, there is shown a schematic view of a

luminaire/illumination system 10 according to an exemplifying embodiment of the present invention having a plurality of LEDs 2 (of which only one is shown) as light sources. A concave reflector 3 is provided to reflect the light 4 emitted by the plurality of LEDs 2. The concave reflector 3 substantially collimates the light 4 such as to hinder glare along the x axis, perpendicular to the elongated axis of the luminaire 10. A plurality of louvers 5 (of which only one is shown) are provided at least partly inside the concave reflector 3, in the light path between the concave reflector 3 and a periphery of the reflected light 6 to hinder glare along the y axis of the luminaire 10. The plurality of louvers 5 is rectangular- shaped with their long axis parallel to the x axis. The plurality of LEDs 2 are positioned on top of the louvers 5, the louvers 5 directing the emitted light 4 and acting as a heat sinking structure for facilitating dissipation of heat emitted from the plurality of LEDs 2, which heat sinking structure thus at least partly is light-transmissive. A remote phosphor 7 is provided between the plurality of louvers 5 and the concave reflector 3, the remote phosphor 7 substantially surrounding the plurality of LEDs 2 such as to convert at least a part of the light 4 emitted by the plurality of LEDs 2. The plurality of LEDs 2 as light sources are shown by way of example and other configurations of light sources may be implemented such as a laser, an incandescent light bulb, a discharge lamp, a fluorescent lamp or the like.

Fig. 3 shows a perspective view of the illumination system of a luminaire 100, according to an exemplifying embodiment of the present invention. A concave reflector 3 is provided to reflect the light emitted by the plurality of LEDs (not illustrated). A plurality of louvers 5 are provided along the y axis along the long axis of the luminaire 100, the louvers 5 provided at least partly inside the concave reflector 3, in the light path between the concave reflector 3 and a periphery of the reflected light. The plurality of louvers 5 is rectangular- shaped with their long axis parallel to the x axis. A remote phosphor 7 is provided between the plurality of louvers 5 and the concave reflector 3, the remote phosphor 7 substantially surrounding the plurality of LEDs. Referring to Fig. 4a, the figure shows a profile view of a louver 5 of the illumination system according to an exemplifying embodiment of the invention. The profile of the louver 5 is rectangular, the rectangle elongated in parallel to the z axis. The louver 5 is formed by a heat-conductive material 11 thereby efficiently dissipating the heat emitted by the at least one light source. The material 11 may be formed by any material with high heat- conductive properties such as copper, aluminum, or the like.

In Fig. 4b, the figure shows a cross-sectional profile view of a louver 5 of the illuminations system according to an exemplifying embodiment of the invention. The louver 5 is coated with a layer 12, such that the layer 12 is arranged to absorb light with wavelengths in the infrared spectrum whilst reflecting light with wavelengths in the visible light spectrum. The layer 12 may be formed by any material with the mentioned properties.

In Fig. 4c, the figure shows a cross-sectional profile view of a louver 5 of the illuminations system according to an exemplifying embodiment of the invention. The louver 5 has an outer portion 13 and an inner portion 14 to provide a temperature difference between the outer 13 and the inner portion 14 such as to provide a lower temperature of the outer portion 13 compared to the temperature of the inner portion 14.

In Fig. 4d, the figure shows a cross-sectional profile view of a louver 5 of the illumination system according to an exemplifying embodiment of the invention. The louver 5 has an outer portion 13 and an inner portion 14, wherein a material is provided between the outer portion 13 and the inner portion 14 to provide a temperature difference between the outer 13 and the inner portion 14.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims. For example, any object as described may take on any other geometrical shape. As an example, the louvers 5 may be plates or tubes with e.g. quadratic, round, or triangular shapes. Further, the concave reflector 3 may be shaped in any other form whilst fulfilling its purpose of reflecting the light 4 from the at least one light sources. As an example, the cross-section of the concave reflector 3 parallel to the x axis may be rectangular, square, or circular.

Moreover, the light sources do not have to be provided adjacent to each other to form an elongated light source, but may instead be segmented into blocks, arrays, circles, or the like. It should also be noted that any combination of the louver properties as disclosed in Fig. 4a-d are possible embodiments of this invention. As an example, the louver 5 as disclosed in Fig. 4c or in Fig. 4d having an outer portion 13 and an inner portion 14 may further be coated with a layer 12 as disclosed in Fig. 4b.

Claims

CLAIMS:

1. An illumination system comprising:

at least one light source;

a heat sinking structure on which the light source is arranged, said structure facilitating dissipation of heat from said light source and being at least partly light- transmissive; and

at least one reflector arranged for reflecting light emitted by said light source, said reflector being arranged in the light emitting direction of the light source and configured to reflect incident light in a direction towards said heat sinking structure.

2. The illumination system as claimed in claim 1, wherein the heat sinking structure provides optical guidance of the light emitted by the at least one light source.

3. The illumination system as claimed in claims 1 or 2, wherein the heat sinking structure substantially collimates the reflected light.

4. The illumination system as claimed in any of the preceding claims, wherein the heat sinking structure comprises louvers.

5. The illumination system as claimed in any one of claims 1-3, wherein the heat sinking structure comprises gratings, grilles, vanes, trellises, lattices or the like.

6. The illumination system as claimed in any of the preceding claims, wherein the at least one light source is a light-emitting diode.

7. The illumination system as claimed in claim 6, further comprising remote phosphor arranged at the at least one light-emitting diode.

8. The illumination system as claimed in claim 6, wherein the at least one light- emitting diode is a white light-emitting diode.

9. The illumination system as claimed in claim 6, wherein the at least one light- emitting diode is a colored light-emitting diode.

10. The illumination system as claimed in any of claims 1-5, wherein the at least one light source is a laser, a incandescent light bulb, a discharge lamp, a fluorescent lamp or the like.

11. The illumination system as claimed in any of the preceding claims, wherein the heat sinking structure is arranged to provide a temperature difference between an outer portion and an inner portion of the heat sinking structure such that a temperature of the outer portion of the heat sinking structure is lower compared to a temperature of the inner portion of the heat sinking structure.

12. The illumination system as claimed in any one of the preceding claims, wherein the heat sinking structure is formed by copper, aluminum, or other heat-conductive material.

13. The illumination system as claimed in any of the preceding claims, wherein the heat sinking structure is coated with a layer arranged to absorb light with wavelengths in the infrared spectrum whilst reflecting light with wavelengths in the visible light spectrum.