This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2014/058562, filed on Apr. 28, 2014, which claims the benefit of European Patent Application No. 13167058.0, filed on May 8, 2013. These applications are hereby incorporated by reference herein.
The present invention relates generally to a lighting device, and more particularly to a solid state lighting device comprising a multiple of light sources, an envelope and a heat spreader element arranged at the envelope.
Lighting devices such as light emitting diode (LED) based light bulbs, or LED lamps, are generally known. A LED lamp concept for a high intensity, high lumen output, is typically limited by its thermal properties and available space for the driver electronics. US 2012/0139403 A1 discloses a solid state lighting device comprising LEDs optically coupled to an optical guide, which optical guide encloses an inner volume, and a thermal guide. The thermal guide is integrated within the optical guide for providing thermal conduction from the LEDs and is either co-extensively proximate to an area of the optical guide or is arranged within the inner volume of the optical guide.
The system described above is generally effective in accomplishing a thermally effective lighting device. However, there is a need for a less complex, less costly lighting device with efficient thermal properties.
It is an object of the present invention to at least provide an improved lighting device. It would be advantageous to achieve a lighting device suitable for a retrofit LED lamp at low cost, which has a low thermal resistance, Rth, on system level. It would also be desirable to enable a lighting device which has a high available volume for the driver electronics, and to provide a good optical performance with the possibility of an omni-directional light distribution. These objects are achieved by a lighting device according to the present invention as defined in the appended independent claim. Preferred embodiments are set forth in the dependent claims and in the following description and drawings.
Thus, in accordance with the present inventive concept, there is provided a lighting device comprising a light source, an envelope comprising an outer surface arranged for distributing light from the multiple of light sources, and an inner surface being configured for surrounding an internal volume. The inner surface is at least partly covered by a sheet metal element, i.e. a heat spreader element arranged at the inner surface. The sheet metal element is separated a predetermined distance from said inner surface, thereby providing a clearance between the inner surface and the sheet metal element, which is advantageous for preventing optical coupling between the sheet metal element and the envelope.
This provides a low cost lighting device which utilizes the inner surface of the envelope to provide a large cooling area. The inner volume of the envelope may then be utilized for positioning of driver electronics of the lighting device. Since the light output from the lighting device is generated at the outer surface of the envelope, advantageously no shadows from the driver electronics or the heat spreader element will be present in the generated light. Sheet metals are generally cheap and flexible, and are further associated with easy shaping and forming technologies, which is advantageous.
According to an embodiment of the lighting device, a portion of the sheet metal element is arranged in direct contact with the inner surface or be thermally connected with the inner surface for instance by means of some thermal coupling agent. Further, at least a portion of the sheet metal element is separated a predetermined distance from the inner surface. Preferably, the predetermined distance is selected between 10 μm and 200 μm, and is typically selected to about 100 μm, to ensure good thermal properties of the lighting device. In an exemplifying embodiment, spacer elements are arranged between the sheet metal element and the inner surface for providing the predetermined distance.
According to an embodiment of the lighting device each of the multiple of light sources is thermally coupled to the sheet metal element to increase the heat transfer from the light sources to the sheet metal element. For LED's with a thermal pad: soldering or applying advanced glue is applicable for thermally coupling the LED's to the sheet metal element. For LED's mounted on a flexible sheet metal element (flex foil) a properly designed flex foil and an adhesive layer, e.g. a LED strip in the Equinox, is applicable for providing a good thermal coupling between the LEDs and the sheet metal element.
The outer surface of the envelope is according to an embodiment of the lighting device arranged with light extraction elements in order to enhance the light output and/or to control the intensity profile or light ray extraction from the outer surface of the envelope.
According to embodiments of the lighting device, the multiple light sources are distributed over a preselected area of the envelope, for instance at the inner surface of, or alternatively on the outer surface of, the envelope. Clusters of light sources may be arranged at selected surface areas. Thereby, the light distribution from the envelope may for instance be evenly spread all over the respective surface, i.e. the light sources are evenly distributed over the entire envelope, or the light distribution is concentrated to specific areas of the envelope. Providing clusters of LEDs (or LEDs) distributed over the surface of the envelope, and thereby the surface of the sheet metal element, is advantageous to provide an improved thermal spreading by means of the sheet metal element. As a consequence, the material of the sheet metal element can be selected to be thinner or less thermally conducting, which opens the possibility to use materials like thin steel sheets.
According to an embodiment of the lighting device, the envelope comprises a light guide which is optically coupled to the multiple of light sources for receiving and distributing light from the light sources. The light is distributed through the light guide by means of internal reflection. In this embodiment, to realize good internal reflection in the light guide, the sheet metal element is preferably separated a predetermined distance from the light guide as previously mentioned. In an embodiment of the lighting device, the light guide is provided with a light input edge at an end surface at its proximal end, and at which the multiple light sources are arranged. The light guide may be arranged as a hollow solid light guide, or be flexible. When being flexible, the light guide is preferably arranged utilizing an outer protective transparent encapsulation layer of the envelope as a support structure.
According to an embodiment of the lighting device, driver electronics of the multiple of light sources is arranged within the internal volume. Thereby, a considerably larger volume is utilized for driver electronics than in known retrofit LED lamps solution, where the driver electronics is typically arranged within the light bulb base. Also, with the arrangement of the present invention, the required volume for driver electronics is not interfering with the surface for light output coupling and light source cooling of the lighting device. When the lighting device is utilized to provide a retrofit lamp, it typically comprises a base coupled to the envelope, which may be an Edison screw base or any other applicable base.
These and other aspects, features, and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
The invention will now be described in more detail and with reference to the appended drawings in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings. The below embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
A sheet metal element 23 is in an alternative embodiment of the lighting device, and as illustrated in
Referring again to
According to an embodiment of the lighting device according to the present inventive concept, the outer surface of the light guide, compare surface 12a in
Referring now to
In an alternative embodiment, which is illustrated in
Reference is now made to
According to embodiments of the lighting device, since the thermal performance of the lighting device is determined by a parameter governed by thermal conductivity times thickness, Kd, of the sheet metal, the thickness of the sheet metal element is selected with respect to the specific sheet metal material, see a graph of a simulation illustrating the thermal resistance Rth from LED area (area where light sources are arranged) to ambient as a function of the value Kd of the heat spreader element, in
With reference now to
in the first extreme situation, a heat load of 8 W is fully distributed over the bulb inner surface, shown in
in the second extreme situation, a heat load of 8 W is applied at the ring area of the neck of the glass bulb, shown in
As can be seen in
To continue with reference to
Examples of solid state light sources applicable for lighting devices according to the invention include light emitting diodes (LEDs), laser diodes, and organic LEDs (OLEDs).
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other 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 measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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13167058 | May 2013 | EP | regional |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP2014/058562 | 4/28/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2014/180689 | 11/13/2014 | WO | A |
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Number | Date | Country | |
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