Abstract:
The invention relates to an electric lamp ( 102 ) comprising a primary semiconductor light source ( 104 ) in thermal communication with a primary reflector ( 106 ). Herein, the primary reflector ( 106 ) is reflective, transparent and/or translucent. The primary reflector ( 106 ) is configured for transferring heat generated by the primary semiconductor light source ( 104 ) during operation away from said primary semiconductor light, source ( 104 ). As a result, the electric lamp ( 102 ) according to the invention effectively reduces the number of parts comprised in the electric lamp ( 102 ), thereby lowering the costs of manufacturing the electric lamp ( 102 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an electric lamp. 
       BACKGROUND OF THE INVENTION 
       [0002]    US-A 2006/001384 A1 discloses a LED lamp including bare LED chips and a lamp shade. The bare LED chips are mounted on the outer surface of an axle extending through the lamp shade. The axle accommodates a heat pipe for dissipating heat generated by the LED chips. For this purpose, the heat pipe may be provided with a heat receiving portion and a heat dissipation portion, between which portions heat is transferred via liquid and gas phase transitions of a fluid sealed inside the pipe. The dissipation portion dissipates heat to the surroundings of the LED lamp via natural or forced convection. 
         [0003]    A disadvantage of the LED lamp disclosed in US-A 2006/001384 A1 is in its rather complex and hence expensive facility for removing heat from the LED chips. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the electric lamp according to the invention to counteract at least one of the disadvantages of the known electric lamp. This object is achieved by the electric lamp according to the invention, which electric lamp comprises a primary semiconductor light source in thermal communication with a primary reflector, wherein the primary reflector is reflective, transparent and/or translucent, and wherein the primary reflector is configured for transferring heat generated by the primary semiconductor light source during operation away from said primary semiconductor light source. 
         [0005]    As the primary reflector is configured for either reflecting or allowing to pass trough light generated by the primary semiconductor light source, as well as for transferring away heat generated by said primary semiconductor light source, the primary reflector effectively integrates the functionality of a lamp shade and the functional character of a heat sink into one single element. As a result, the electric lamp according to the invention effectively reduces the number of parts comprised in an electric lamp, thereby simplifying the construction of an electric lamp as well as lowering the costs associated with manufacturing said electric lamp. 
         [0006]    The primary reflector is reflective, transparent and/or translucent. Hence, for example, a first part of the primary reflector may be reflective whereas a second part of the primary reflector may be transparent. Basically, the primary reflector may be provided with any combination of the aforementioned optical properties. The primary reflector is not to absorb the light generated during operation by the primary semiconductor light source. 
         [0007]    In this text, a semiconductor light source includes, but is not limited to, Light Emitting Diodes (LEDs), Organic Light Emitting Diodes (OLEDs) and opto-electrical devices. 
         [0008]    In this text, thermal communication between objects means that said objects are connectable via heat transfer. The latter heat transfer causes the temperatures of the objects to mutually correlate. In practice, this means that fluctuations in a first temperature, i.e. the temperature of a first object, are similarly followed by a second temperature, i.e. the temperature of a second object. In this text, said mutual correlation of temperatures implies that fluctuations in the first temperature are followed by the second temperature according to a thermal process having a time constant smaller than one hour. Preferably said time constant is smaller than 10 minutes, more preferably it is smaller than 1 minute. A significant thermal resistance, i.e. a thermal isolation, installed between objects prevents them from being in thermal communication. In this text, thermal communication between objects requires any thermal resistance present there between to be smaller than 10 K/W. 
         [0009]    In this text, a reflector is not limited to having a particular geometry. However, if the reflector is reflective, the geometry of the reflector is confined to the extent that it allows for reflecting the light generated by the semiconductor light source during operation. In this text, the reflectance of light is defined with respect to the primary optical axis of the primary semiconductor light source which is an imaginary vector whose orientation coincides with the axis along which there is rotational symmetry with respect to the light intensity distribution of the primary semiconductor light source, and whose direction coincides with the direction at Which most light propagates from the primary semiconductor light source. Reflection is obtained if at least 80% of the light emitted in a backward direction, i.e. a direction having a component opposite to the direction of the primary optical axis, is reflected along a direction haying a component equal to the direction of the primary optical axis. Preferably, the primary reflector is arranged substantially perpendicular to the primary optical axis. As an example, a plate like geometry will for prove useful for reflecting light produced by the primary semiconductor light source, provided the plate and the primary semiconductor light source are mutually situated such that light emitted in backward direction indeed arrives at the plate rather than passing by the plate. In this text, a plate is understood to imply a geometry that is flat, slightly curved or substantially curved, and for which the ratio of in-plane dimensions to the thickness is substantially large, i.e. exceeding 10. Hence, the rim of the plate seems less appropriate for the purpose of reflecting light generated by the primary semiconductor light source. 
         [0010]    Examples of materials having relatively high thermal conductivity and providing significant reflection are metals such as aluminum or chromium. Alternatively, metals provided with a reflective coating based on e.g. aluminum, titanium dioxide, aluminum oxide or barium sulphate may be successfully employed. A material suitable for manufacturing a translucent primary reflector is Poly Crystalline Aluminum (PCA). 
         [0011]    A preferred embodiment of the electric lamp according to the invention comprises a printed circuit board for materializing thermal communication between the primary semiconductor light source and the primary reflector. A printed circuit board provides for significant contact area between the primary semiconductor light source and the primary reflector, thereby materializing substantially thermal conductivity between the primary semiconductor light source and the primary reflector. Therefore, this embodiment is advantageous in that it further facilitates the thermal communication between the primary semiconductor light source and the primary reflector. 
         [0012]    A further preferred embodiment of the electric lamp according to the invention comprises a cage for mechanically connecting the primary reflector to a socket. This embodiment increases the area of the primary reflector that is exposed to a fluid, i.e. air, thereby increasing heat transfer via convection from the primary reflector towards the surrounding air. As a result, this embodiment advantageously increases the ability of the primary reflector to transfer away heat from the primary semiconductor light source. 
         [0013]    A further preferred embodiment of the electric lamp according to the invention comprises a secondary semiconductor light source in thermal communication with the primary reflector, wherein the primary and secondary semiconductor light sources are situated on mutually opposite sides relative to the primary reflector. This embodiment has the advantage of generating more light during operation. 
         [0014]    A further preferred embodiment of the electric lamp according to the invention comprises a secondary semiconductor light source in thermal communication with a secondary reflector, wherein the secondary reflector is reflective, transparent and/or translucent, and wherein secondary reflector is configured for transferring heat generated by the secondary semiconductor light source during operation away from said secondary semiconductor light source. This embodiment advantageously allows for increasing the amount of light producible by the electric lamp while maintaining to some extent the surface area available per semiconductor light source for transferring away heat via convection. 
         [0015]    In a practical embodiment of the electric lamp according to the invention, the primary reflector and the secondary reflector are mutually substantially parallel. In this text, objects are considered to be substantially parallel if the distance between said objects varies no more than 10% relative to the length the objects measure along the direction along which the objects are parallel. 
         [0016]    In a further preferred embodiment of the electric lamp according to the invention, a distance between the primary reflector and the secondary reflector is larger than 6 mm and smaller than 8 mm if the primary reflector and the secondary reflector are reflective. Through selecting the distance no larger than 8 mm, the distribution of the light generated by the primary and the secondary semiconductor is negligibly disturbed by the distance between the reflective primary and secondary reflectors. By choosing the distance no smaller than 6 mm, transfer of heat from the primary and secondary reflectors via natural convection is enabled. Therefore, this embodiment is advantageous in that it significantly increases the capability of the electric lamp to remove heat from the semiconductor light sources without disturbing the light distribution. 
         [0017]    In a further preferred embodiment of the electric lamp according to the invention, a distance between the primary reflector and the secondary reflector is larger than 6 mm and smaller than 15 mm if the primary reflector and the secondary reflector are transparent and/or translucent. Through selecting the distance smaller than 15 mm, the distribution of the light generated by the primary and the secondary semiconductor is negligibly disturbed by the distance between the transparent and/or translucent primary and secondary reflectors. By choosing the distance larger than 6 mm, transfer of heat from the primary and secondary reflectors via natural convection is enabled. Therefore, this embodiment is advantageous in that it significantly increases the capability of the electric lamp to remove heat from the semiconductor light sources without disturbing the light distribution. 
         [0018]    In a further preferred embodiment of the electric lamp according to the invention, the primary semiconductor light source is situated on a side of the primary reflector facing away from the secondary reflector, and wherein the secondary semiconductor light source is situated on a side of the secondary reflector facing away from the primary reflector. In this embodiment, radiation induced heating of the primary reflector by the secondary semiconductor light source, as well as radiation induced heating of the secondary reflector by the primary semiconductor light source, are effectively minimized. As a result, this embodiment advantageously increases the efficiency with which the primary reflector is enabled to remove heat from the primary semiconductor light source, as well as the efficiency with which the secondary reflector is enabled to remove heat from the second semiconductor light source. 
         [0019]    In a further preferred embodiment of the electric lamp according to the invention, the primary reflector comprises a covered surface area which is covered by the primary semiconductor light source and a further surface area, and wherein the further surface area is larger than the covered surface area. This embodiment enables the primary reflector to have significant area available for reflecting light and for transferring heat via convection. Therefore this embodiment is advantageous in that it makes the functionality of the primary reflector robust for the dimensions of the primary semiconductor light source. 
         [0020]    In a further preferred embodiment of the electric lamp according to the invention, the primary reflector comprises ceramic material. Ceramic materials are marked by having a relatively high reflectivity while providing sufficient thermal conductivity. Therefore this embodiment has the advantage of omitting the need for providing the primary reflector with a reflective coating, thereby reducing the number of processing steps required for manufacturing the electric lamp. 
         [0021]    In a further preferred embodiment of the electric lamp according to the invention, the primary reflector is configured for performing as a ceramic printed circuit board. Owing to the significant electrical resistance present in ceramic materials, this embodiment advantageously enables integration of the printed circuit board and the primary reflector, thereby further reducing the number of components comprised in the electric lamp. 
         [0022]    A further practical embodiment of the electric lamp according to the invention comprises a transparent optical chamber mounted to the primary reflector for accommodating the semiconductor light source. 
         [0023]    In a further preferred embodiment of the electric lamp according to the invention, the transparent optical chamber comprises transparent ceramic material. Since the thermal conduction of transparent ceramic materials largely exceeds the thermal conduction associated with commonly used transparent materials such as plastics or glass, in this embodiment the transparent optical chamber additionally performs as a heat sink. As a result, this embodiment allows for more effectively cooling the primary semiconductor light source. 
     
    
     
       SHORT DESCRIPTION OF THE FIGURES 
         [0024]      FIG. 1A  schematically depicts an embodiment of the electric lamp according to the invention comprising primary and secondary semiconductor light sources. 
           [0025]      FIG. 1B  provides a three-dimensional image of the embodiment depicted in  FIG. 1A . 
           [0026]      FIG. 2A  schematically displays an embodiment of the electric lamp according to the invention comprising primary and secondary reflectors. 
           [0027]      FIG. 2B  provides a three-dimensional image of the embodiment depicted in  FIG. 2A . 
           [0028]      FIG. 3  schematically shows an electric lamp comprising a cage for mechanically connecting a primary reflector to a socket. 
           [0029]      FIG. 4  schematically displays an embodiment of the electric lamp according to the invention comprising mutually parallel primary and secondary reflectors, mutually arranged at a distance substantially equal to a thickness of the primary reflector and a thickness of the secondary reflector. 
           [0030]      FIG. 5  schematically depicts an embodiment of the electric lamp according to the invention comprising substantially curved primary and secondary reflectors. 
           [0031]      FIG. 6  schematically displays an embodiment of the electric lamp according to the invention comprising primary and secondary reflectors provided with indentations surrounding the primary and secondary semiconductor light sources. 
           [0032]      FIG. 7A  schematically depicts a bottom view of an embodiment of the electric lamp according to the invention comprising four substantially curved reflectors. 
           [0033]      FIG. 7B  schematically displays a plan view of the embodiment depicted in  FIG. 7A . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0034]      FIG. 1A  schematically depicts an electric lamp  102  comprising a primary semiconductor light source  104  having a primary optical axis  105 , and being in thermal communication with a reflective primary reflector  106 . The primary reflector is configured for reflecting light generated by the primary semiconductor light source  104  during operation. For that purpose, the primary reflector  106  may be manufactured from a ceramic material, Additionally, the primary reflector  106  is arranged for transferring away heat generated by said primary semiconductor light source  104  during operation. In a further embodiment, the primary reflector  106  comprises a covered surface area which is covered by the primary semiconductor light source  104  and a. further surface area, and wherein the further surface area is larger than the covered surface area, preferably two times larger and more preferably three times larger. In this specific example, the electric lamp  102  furthermore comprises a secondary semiconductor light source  108  having a secondary optical axis  109 . Herein, the primary and secondary semiconductor light sources  104  and  108  are situated on mutually opposite sides of the primary reflector  106 . In this particular example, a primary printed circuit board  110  is situated between the primary semiconductor light source  104  and the primary reflector  106  as to provide thermal communication there between. Likewise, a secondary printed circuit board  112  is installed between the secondary semiconductor light source  108  and the primary reflector  106  for the purpose of thermal communication between. Optionally, transparent optical chambers  114  and  116  are mounted to the primary reflector  106  for accommodating the primary and secondary semiconductor light sources  104  and  108 , respectively. Preferably, the transparent optical chambers  114  and  116  are manufactured from a transparent ceramic material such as aluminum oxide. The primary reflector  106  may be mechanically connected to a socket  118 , which socket  118  is arranged for providing electrical energy to the primary and secondary semiconductor light sources  104  and  108  via the primary and secondary printed circuit boards  110  and  112 , respectively. 
         [0035]      FIG. 2A  schematically depicts an electric lamp  202  comprising a primary semiconductor light source  204  having a primary optical axis  205 , and being in thermal communication with a primary reflector  206 . Said primary reflector  206  is arranged for transferring away heat generated by the primary semiconductor light source  204  during operation. The electric lamp furthermore comprises a secondary semiconductor light source  208  having a secondary optical axis  209 , and being in thermal communication with a secondary reflector  210 . The secondary reflector  210  is configured for transferring away heat generated by the secondary semiconductor light source  208  during operation. In this particular embodiment, the primary and secondary reflectors  206  and  210  are mounted in a mutually substantially parallel configuration. Herein, the primary semiconductor light source  204  is situated on a side of the primary reflector  206  facing away from the secondary reflector  210 , whereas the secondary semiconductor light source  208  is situated on a side of the secondary reflector  210  facing away from the primary reflector  206 . The primary and secondary semiconductor light sources  204  and  208  are in electrical connection with a printed circuit board  212 , which printed circuit board may be provided with electrical power via a socket  214 . Alternatively, a battery may be employed for the purpose of providing electrical power to the printed circuit board  212 . Optionally, transparent optical chambers  216  and  218  are mounted to the primary reflector  206  and the secondary reflector  210 , respectively, for accommodating the primary and secondary semiconductor light sources  204  and  208 . In this particular embodiment an area of the primary reflector  206  underneath the optical chamber  216  is reflective. The remaining area of the primary reflector  206  is transparent. Likewise, an area of the secondary reflector  210  underneath the optical chamber  218  is reflective whereas the remaining area of the primary reflector  210  is transparent. 
         [0036]      FIG. 3  schematically depicts an electric lamp  302  comprising a primary semiconductor light source  304  having a primary optical axis  305  and thermally connected to a reflective primary reflector  306 . The primary reflector  306  is capable both of reflecting light generated by the primary semiconductor light source  304  during operation and of transferring away heat generated by the semiconductor light source  304  during operational conditions. The primary reflector  306  is mechanically connected to a socket  310  via a cage  308 . Herein, said cage  3080  is generally an open structure, for instance a structure comprising a plurality of bars  312 . A primary transparent optical chamber  314  may be mounted to the primary reflector  306 . Preferably the primary transparent optical chamber  314  is manufactured from a transparent ceramic material as to increase heat transfer. 
         [0037]      FIG. 4  schematically depicts an electric lamp  402  comprising a primary semiconductor light source  404  in thermal communication with a translucent primary reflector  406 . Said primary reflector  406  is arranged for transferring away heat generated by the primary semiconductor light source  404  during operation. The electric lamp furthermore comprises a secondary semiconductor light source  408  in thermal communication with a translucent secondary reflector  410 . The secondary reflector  410  is configured for transferring away heat generated by the secondary semiconductor light source  408  during operation. In this particular embodiment, the primary and secondary reflectors  406  and  410  are mounted in a mutually substantially parallel configuration. Furthermore, in this particular example, the distance d 1  between the primary reflector  406  and the secondary reflector  410  amounts to 7 mm. 
         [0038]    Preferably the primary and secondary reflectors  406  and  410  are manufactured from ceramic material, e.g. magnesium silicate. Owing to the significant electrical resistance of the latter material the primary and secondary reflectors  406  and  410  are enabled to perform as ceramic printed circuit boards, i.e. encompassing printed circuit boards, without installing further electrical insulation for that purpose. Herein, the primary and secondary semiconductor light sources  404  and  408  are situated on mutually opposite sides relative to the structure composed of the primary and secondary reflectors  406  and  410 . The primary and secondary reflectors  406  and  410  are in electrical connection with a socket  412 . Transparent optical Chambers  416  and  418  are optionally mounted to the primary reflector  406  and the secondary reflector  410 , respectively, for accommodating the primary and secondary semiconductor light sources  404  and  408 . Preferably, the transparent optical chambers  416  and  418  are manufactured from a transparent ceramic material. 
         [0039]      FIG. 5  schematically depicts an electric lamp  502  comprising a primary semiconductor light source  504  accommodated in a primary transparent optical chamber  506 . The primary semiconductor light source  504  has a primary optical axis  508 . The primary semiconductor light source  504  is thermally connected to a reflective primary reflector  510 . The primary reflector  510  is capable both of reflecting light generated by the primary semiconductor light source  504  during operation and of transferring away heat generated by the primary semiconductor light source  504  during operational conditions. The electric lamp  502  furthermore comprises a secondary semiconductor light source  512  being accommodated in a secondary transparent optical chamber  514 , having a secondary optical axis  516  and being thermal communication with a reflective secondary reflector  518 . The secondary reflector  518  is configured for reflecting light generated by the secondary semiconductor light source  512  during operation, as well as for transferring away heat generated by the secondary semiconductor light source  512  during operational conditions. The primary and secondary reflectors  510  and  518  are substantially curved. For increasing the ability to reflect light along a direction having a substantial component parallel to the primary and secondary optical axes  508  and  516 , the primary and secondary reflectors  510  and  518  are concave with respect to the primary and secondary semiconductor light sources  504  and  512 , respectively. The primary and secondary reflectors  510  and  518  are mechanically connected to a socket  520 . 
         [0040]      FIG. 6  schematically displays an electric lamp  602  comprising a primary semiconductor light source  604  having a primary optical axis  606 . The primary semiconductor light source  604  is thermally connected to a primary reflector  608 . The primary reflector  608  is capable of transferring away heat generated by the primary semiconductor light source  604  during operational conditions. The electric lamp  602  furthermore comprises a secondary semiconductor light source  610  which has a secondary optical axis  612 , and which is in thermal communication with a secondary reflector  614 . The secondary reflector  614  is configured for transferring away heat generated by the secondary semiconductor light source  610  during operational conditions. For focusing light emitted in backward directions towards directions alike the primary and secondary optical axes  606  and  612 , the primary and secondary reflectors  608  and  614  are provided with local indentations surrounding the primary and secondary semiconductor light sources  604  and  612 , respectively. For the purpose of reflection, the primary and secondary reflectors  608  and  614  are reflective within said local indentations. Aside from said local indentations, the primary and secondary reflectors  608  and  614  are transparent. The primary and secondary reflectors  608  and  614  are mechanically connected to a socket  616 . 
         [0041]      FIG. 7A  schematically depicts an electric lamp  702  by way of a bottom view. The electric lamp comprises a primary semiconductor light source  704  and a secondary semiconductor light source  706 , which are mounted in thermal communication to a primary reflector  708  and a secondary reflector  710 , respectively. Referring to  FIG. 7B , the primary semiconductor light source  704  is provided with a primary optical axis  705  whereas the secondary semiconductor light source  706  has a secondary optical axis  707 . The primary and secondary reflectors  708  and  710  are configured for both reflecting light generated during operation by the primary and secondary semiconductor light sources  704  and  706 , and for transferring away heat from said primary and secondary semiconductor light sources  704  and  706 , respectively. Referring to  FIG. 7A , the electric lamp  702  furthermore comprises a third semiconductor light source  712  and a fourth semiconductor light source  714 . The third and fourth semiconductor light sources  712  and  714  are in thermal communication with third and fourth reflectors  716  and  718 , respectively. The primary and secondary reflectors  708  and  710  are configured for both reflecting light generated during operation by the primary and secondary semiconductor light sources  704  and  706 , and for transferring away heat from said primary and secondary semiconductor light sources  704  and  706 , respectively. As apparent from  FIG. 7B , the primary and secondary reflectors  708  and  710  are substantially curved as to focus the light generated during operation by the primary and secondary semiconductor light sources  704  and  706  in particular directions. Preferably, the curvature of the primary and secondary reflectors is adjustable, e.g. by manufacturing the primary and secondary reflectors from a material allowing for significant plastic deformation, as to enable the focusing of light in any direction desired. All reflectors may be mechanically mounted to a socket  720 . 
         [0042]    While the invention has been illustrated and described in detail in the drawings and in the foregoing description, the illustrations and the description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. It is noted that the system according to the invention and all its components can be made by applying processes and materials known per se. In the set of claims and the description the word “comprising” does not exclude other elements and the indefinite article “a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope. It is further noted that all possible combinations of features as defined in the set of claims are part of the invention.