Abstract:
The present invention relates to a light output device ( 10 ) comprising a heat sink ( 12 ); a substrate ( 14 ) with at least one light emitting element ( 24 ) arranged thereon; and an optical component ( 16 ), wherein the optical component is mounted to the heat sink by means of a bayonet type mechanism, and wherein the substrate is fixed between the heat sink and the optical component. The present invention also relates to a method of assembling such a light output device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a light output device, in particular a light output device comprising at least one light emitting diode (LED), as well as a method of assembling such a light output device. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally, printed circuit boards (PCBs) with LEDs are often glued, screwed or clamped to a heat sink to ensure thermal contact and sufficient heat conduction away from the LEDs. Also, often optics are placed over the LEDs to provide a desired radiation pattern or to protect the LED. 
         [0003]    U.S. Pat. No. 7,348,604 (Matheson) discloses a light-emitting module comprising heat dissipation element, a substrate coupled to one or more light emitting elements, and a housing element including fastening means for coupling the housing element to the heat dissipation element, the substrate allegedly being enclosed between the heat dissipation element and the housing element. The housing element is provided with an optical element, and it is flexible to be slid over the heat dissipation element and clutch the latter as it resumes its unstrained shape. 
         [0004]    A drawback with the solution presented in Matheson is that the flexible property of the housing element imposes design constraints on the housing element with respect to material and shape selection. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to at least partly overcome this drawback, and to provide an improved light output device. 
         [0006]    This and other objects that will be apparent from the following description are achieved by a light output device, and a method of assembling such a light output device, according to the appended independent claims. 
         [0007]    According to an aspect of the present invention, there is provided a light output device, comprising: a heat sink; a substrate with at least one light emitting element arranged thereon; and an optical component, wherein the optical component is mounted to the heat sink by means of a bayonet type mechanism, and wherein the substrate is fixed between the heat sink and the optical component. 
         [0008]    A bayonet type mechanism may generally be defined as an arrangement for fastening with a short rotational movement two connecting parts of rotary symmetrical character to each other. By using a bayonet type mechanism, simply twisting the optical component may fixate the optical component in the right position and also fixate the substrate to the heat sink. The latter ensures thermal contact between the substrate and the heat sink. Fixation of the substrate to the heat sink is thus advantageously carried out without having to use flexible elements, or screws, glue or other additional components. Also, the substrate may be forced to the heat sink where it is needed: namely around the at least one LED. 
         [0009]    In one embodiment, the bayonet type mechanism comprises two opposite lateral members protruding from the optical component and two opposite grooves in the heat sink adapted to receive said protruding members, as the optical component is rotated appropriately. The optical element may for instance include a base plate having the shape of a rectangle with two diagonally opposite rounded corners, and the heat sink may be formed as a profiled channel with two longitudinal, inner grooves. Thus, the function of fixating the substrate to the heat sink is integrated mainly in the optical element. 
         [0010]    Preferably, the substrate is a printed circuit board, the optical component is a collimating lens, and the at least one light emitting element is at least one light emitting diode (chip or package). Benefits of LEDs include high efficiency, long useful life, etc. Alternative substrates include, but are not limited to, a wired circuit board. Alternative optical components include, but are not limited to, a protective transparent or translucent cover, a diffusing cover, a lens, a reflector, etc. Alternative light emitting elements include, but are not limited to, organic light emitting diodes (OLEDs), laser diodes, etc. 
         [0011]    According to another aspect of the present invention, there is provided a method of assembling a light output device, the method comprising: providing a heat sink; placing a substrate with at least one light emitting element arranged thereon on the heat sink; and mounting an optical component to the heat sink by means of a bayonet mechanism such that the substrate is fixed between the heat sink and the optical component. In one embodiment, the bayonet type mechanism comprises two opposite lateral members protruding from the optical component and two opposite grooves in the heat sink, wherein mounting the optical component to the heat sink comprises rotating the optical component in relation to the heat sink such that the protruding members are received in the grooves. In particular, the optical component is preferably mounted to the heat sink by rotating it about 30-150 degrees, preferably about 45 degrees, i.e. a short rotary movement, compared to for instance a screw fitting which requires a long rotary movement for a similar function. Moreover, this aspect exhibits similar advantages and may exhibit similar features as the aspect discussed above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention. 
           [0013]      FIGS. 1   a - 5   b  are perspective views and side views, respectively, illustrating steps of assembling a light output device according to an embodiment of the present invention. 
           [0014]      FIG. 6   a  is a perspective view and  FIG. 6   b  is a cross-sectional side view of an optical element of the present light output device. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A light output device  10  according to an embodiment of the present invention will now be described with reference to the appended drawings. 
         [0016]    The light output device  10  comprises a heat sink  12 , a PCB  14 , and an optical component  16 . 
         [0017]    The heat sink  12  is preferably made of a material with high thermal conductivity, such as metal, in particular aluminum. The present heat sink  12  is a profiled channel having a base portion  18  and two side wall portions  20   a ,  20   b . Two opposite grooves  22   a ,  22   b  run along the inside of the wall portion  20   a ,  20   b  near the base portion  18 , as illustrated in e.g.  FIGS. 1   a - 1   b . The heat sink  12  may optionally comprise a plurality of fins for enhanced heat dissipation. 
         [0018]    The PCB  14  comprises at least one LED  24  thermally connected thereto. The LED  24  may be an LED package, or a chip or die mounted directly on the PCB  14 . The PCB  14  further comprises electrically conductive traces  26  or the like for electrically connecting the LED(s)  24  to a power source (not shown), for activation of the LED(s)  24 . The PCB  14  rests, preferably directly, on the base portion  18  between the two wall portions  20   a ,  20   b  of the heat sink  12 . Also, opposite edges  28   a ,  28   b  of the PCB  14  may abut the inside of the wall portions  20   a ,  20   b , as illustrated in e.g.  FIG. 2   b , thereby preventing movement of the PCB  14  transversal to the wall portions  20   a ,  20   b.    
         [0019]    The optical component  16  comprises a body portion made of e.g. polycarbonate or PMMA with a cylindrical outside  30  and a sloping inside  32  (see  FIGS. 6   a - 6   b ), the latter serving as a collimating reflector based on total internal reflection (TIR). The optical component  16  further comprises a central opening  34  where the at least one LED  14  is to be placed. Also, the optical component  16  comprises a base plate  36  facing the base portion  18  of the heat sink  12 . The base plate  36  is substantially rigid, and the optical component  16  including the base plate  36  may be integrally formed in one piece. The base plate  36  has the overall shape of a rectangle with two rounded corners  38   a ,  38   b , as illustrated. The (perpendicular) distance d 1  between the shorter sides  40   a ,  40   b  of the rectangular base plate  36  is substantially equal to the distance d 2  between the bottom of the grooves  22   a ,  22   b , whereas the corresponding distance between the other sides of the rectangular base plate  34  is shorter. Further, the thickness of the base plate  36  is preferably selected such that it may be jammed in the grooves  22   a ,  22   b . Alternatively, wedges  42   a ,  42   b  may be provided at the shorter sides  40   a ,  40   b  for this purpose. 
         [0020]    In the state illustrated in  FIGS. 5   a  and  5   b , the optical component  16  is placed over the PCB  14  and rotated such that at least portions of the shorter sides  40   a ,  40   b  of the rectangular base plate  36  are received in the grooves  22   a ,  22   b . This prevents movement of the optical component  16  transversal to the base portion  18  of the heat sink. Further, movement of the optical component  16  transversal to the wall portions  20   a ,  20   b  is prevented. The connection between the optical component  16   a  and the heat sink  12  additionally applies a pressure or force to the PCB  14 , which PCB  14  is inlayed or mechanically sandwiched between the optical component  16  and the heat sink  12 , such that the PCB  14  is pressed against the heat sink  12 , thereby fixating the PCB  14  to the heat sink  12  and establishing a desired level of thermal contact between the PCB  14  and the heat sink  12 . This may be achieved by appropriately selecting the thickness of the PCB  14  in relation to the distance between the base portion  18  and the grooves  22   a ,  22   b  of the heat sink  12 . No additional components except of the optical component  16  are needed to fixate the PCB  14  to the heat sink  12 . Also, the optical component  16  designed as described above may seal the LED  24  from the outside. This beneficially allows filling the device or module  10  outside the optical component  16  with a filling/potting material (not shown) to protect the LED  24  from water or moisture, without the filling/potting material entering the central opening or optical cavity  34  from the underside. 
         [0021]    Longitudinal movement of the PCB  14  and the optical component  16  along the wall portions  20   a ,  20   b  is prevented as portions of the base plate  34  are jammed in the grooves  22   a ,  22   b . End caps may optionally be used. 
         [0022]    Upon operation of the light output device  10 , current is supplied to the LED(s)  24  via the electrically conductive traces  26  of the PCB  14 , whereby the at least one LED  24  emits light. The radiation pattern of the emitted light may be shaped by the optical component  16 . Here, the emitted light is collimated. Further, heat generated by the LED(s)  24  is effectively transferred by direct thermal contact from the PCB  14  to the heat sink  12 , for cooling of the LED(s)  24 . 
         [0023]    A method of assembling the light output device  10  according to an embodiment of the present invention will now be described. 
         [0024]    First, in step S1 ( FIGS. 1   a - 1   b ), the heat sink  12  is provided. 
         [0025]    Then, in step S2 ( FIGS. 2   a - 2   b ), the PCB  14  is placed on the base portion  18  between the side wall portions  20   a ,  20   b  of the heat sink  12 . The at least one LED  24  is preferably mounted to the PCB  14  prior to the PCB  14  being placed on the heat sink  12 , but it could alternatively be mounted to the PCB  14  subsequent to the PCB  14  being placed on the heat sink  12 . 
         [0026]    Then, in step S3 ( FIGS. 3   a - 3   b ), the optical component  16  is introduced, e.g. from above, into the space between the wall portions  20   a ,  20   b  and placed on the PCB  14 , with the opening  34  aligned with the at least one LED  24 . Here, the optical component  16  is oriented such that the sides of the base plate  36  are oriented at about  45  degrees to the side wall portions  20   a ,  20   b  of the heat sink  12 , as illustrated. 
         [0027]    Thereafter, the optical component  16  is rotated (step S4) around a central axis  44  of the optical component  16 , which axis  44  is perpendicular to the plane of the base portion  18  of the heat sink  12 . The optical component  16  may be rotated manually or automatically by means of a machine. 
         [0028]    In  FIGS. 4   a - 4   b , the optical element  16  is rotated clockwise about 22.5 degrees from its initial position, whereas in  FIGS. 5   a - 5   b  the optical element  16  is in its final position, where it is rotated clockwise about 45 degrees from its initial position. In this final position or state, as discussed above, at least portions of the shorter sides  40   a ,  40   b  of the rectangular base plate  36  are received in the grooves  22   a ,  22   b , whereby the optical element  16  is locked in the heat sink  12 , and the PCB  14  is fixed between the heat sink  12  and the optical component  16 . 
         [0029]    As appreciated, the base plate  36  should be sized so as to first allow the optical component  16  to be introduced into the space between the wall portions  20   a ,  20   b  and then allow it to rotate the full 45 degrees when the base plate  36  is in level with the grooves  22   a ,  22   b . Further, the optical element  16  may be provided with protrusions mating with at least one slit in the PCB  14 , or vice versa, for guiding the optical element  16  on the PCB  14 , ensuring proper alignment of the optical element  16  on the PCB  14  and also controlling the rotary motion of the optical element  16  on the PCB  14 . The protrusion may for instance be two downright pins  46   a ,  46   b  extending from the underside of the optical element  16  (see  FIG. 6   a ), whereas the at least one slit may be two curved slits  48   a ,  48   b  (see  FIG. 2   a ) provided in the PCB  14  around the LED  24 . This solution is easier in production, compared to a solution where the PCB has the pins and the optical element has the recess(es). The length of the curved slits  48   a ,  48   b  should preferably match the angle of rotation that is needed between the initial state and the final state of the optical element  16 . At an angle of rotation equal to about 45 degrees as above, the two curved slits  48   a ,  48   b  may be sufficiently short to allow some place on the PCB  14  for the traces  26  and maintain an adequate mechanical stiffness of the PCB  14 . 
         [0030]    The device and method described above may beneficially be used in all applications that use LEDs on a PCB, combined with an optical component. 
         [0031]    The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For instance, several PCBs and optical components could be arranged on a single heat sink.