Patent Publication Number: US-2013242558-A1

Title: Luminaire and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No.2012-062523, filed on Mar. 19, 2012; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Exemplary embodiments described herein generally relate to a luminaire and a method of manufacturing the same. 
     BACKGROUND 
     Luminaires having solid light-emitting elements such as light-emitting diodes (LEDs) as light sources become popular. The solid light-emitting elements may be used in luminaires for various applications owing to the small power consumption and the long lifetime thereof, In contrast, the solid light-emitting elements have the property that the light-emitting efficiency is lowered with increase in operating temperature. When the solid light-emitting elements are operated in a hot environment, the lifetime is shortened. Therefore, a thermal radiation design is important in the luminaires including the solid light-emitting elements employed therein. 
     However, with the design making the thermal radiation a primary concern, the size of a housing may be increased, and hence the light-distribution property may be limited. Therefore, a luminaire which achieves improvement both in thermal radiation and light-distribution property is required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic cross-sectional views illustrating a luminaire according to an embodiment; 
         FIG. 2  is a schematic drawing illustrating an outline of the luminaire; 
         FIGS. 3A and 3B  are schematic drawings illustrating a casing of the luminaire; 
         FIG. 4  is a partial cross-sectional view schematically illustrating an engagement part of the luminaire; and 
         FIG. 5  is a schematic drawing illustrating an example of installation of the luminaire. 
     
    
    
     DETAILED DESCRIPTION 
     A luminaire according to an embodiment includes a light-emitting portion including a light-emitting element, a power control unit configured to supply electric power to the light-emitting portion, an external terminal configured to connect the power control unit and an external power source, and a ceramic housing including the power control unit housed therein, the light-emitting portion mounted on one side of the ceramic housing and the external terminal mounted on the other side of the ceramic housing, and configured to allow at least part of light radiated from the light-emitting element to pass therethrough. 
     Referring now to the drawings, embodiments will be described below. For reference, the same components in the drawings are designated by the same reference numerals and detailed descriptions thereof are omitted as needed, and different parts will be mainly described. 
     Referring now to  FIGS. 1A ,  1 B and  FIG. 2 , a luminaire  100  according to an embodiment will be described. The luminaire  100  is a bulb type lamp including a solid light-emitting element.  FIG. 1A  is a cross-sectional view taken along the line A-A in  FIG. 2 , and illustrates a top view having a light-emitting portion  10  mounted thereon.  FIG. 1B  is a cross-sectional view taken along the line B-B in  FIG. 2 .  FIG. 2  is a schematic drawing illustrating the outline of the luminaire  100 . 
     The luminaire  100  includes a light-emitting portion  10  having a light-emitting element  13 , a power control unit  30  configured to supply electric power to the light-emitting portion  10 , and an external terminal  40  configured to connect the power control unit  30  and an external power source, not shown. The luminaire  100  further includes a ceramic housing  20  having the power control unit  30  housed therein and a cover  60  configured to cover the light-emitting portion  10 . 
     The ceramic housing  20  includes a mounting portion  23  for the light-emitting portion  10  and a mounting portion  25  for the external terminal  40 . The cover  60  is connected to one end of the ceramic housing  20  and covers the light-emitting portion  10 . The ceramic housing  20  and the cover  60  both have translucency, and allow at least part of light radiated from the light-emitting element  13  to pass therethrough. 
     The light-emitting portion  10  includes at least one piece of the light-emitting element  13 , and a base  15  to which the light-emitting elements  13  are secured. The base  15  preferably allows at least part of the light radiated from the light-emitting elements  13  to pass therethrough. The light-emitting elements  13  are sealed by resin containing a phosphor. For example, a white light source is achieved by sealing a blue LED by a resin containing a YAG phosphor. 
     Examples of the light-emitting element  13  includes a light-emitting diode (LED). When a gallium nitride (GaN)-based compound semiconductor is used as a material of an active layer, a short-wavelength light having a wavelength of 500 nanometer or less is obtained. However, the material of an active layer is not limited to the gallium nitride-based compound semiconductor. 
     Examples of the light-emitting element  13  include an organic light-emitting diode (OLED), an inorganic electro luminescence light-emitting element, an organic electro luminescence light-emitting element, or other electroluminescence-type light-emitting elements in addition to the light-emitting diode. 
     As shown in  FIG. 1A , the light-emitting elements  13  are secured on the circular base  15 . A material having a high coefficient of thermal conductivity is preferably used for the base  15 . For example, a translucent resin substrate and a ceramic substrate may also be used. A sapphire substrate or a SiC substrate may be used. 
     A wiring pattern, not shown, is formed on an upper surface of the base  15 , and four of the light-emitting elements  13  are mounted on the wiring pattern. The light-emitting elements  13  are, for example, LED chips, and are secured using silver (Ag) paste or an adhesive agent, and are connected to the wiring via a metallic wire. The light-emitting elements  13  may have a form stored in a package such as a SMD (Surface Mount Device). 
     The light-emitting portion  10  is secured to the mounting portion  23  of the ceramic housing  20  using fixing members  19  such as screws. The power control unit  30  is connected to the light-emitting portion  10 . 
     As shown in  FIG. 1B , the power control unit  30  is arranged in the interior of the ceramic housing  20 , and electrically connected to the light-emitting portion  10  via a lead wire  37 . The power control unit  30  is, for example, an AC-DC converter and configured to convert an AC voltage 100V to a DC voltage 24V and supplies a predetermined drive current to the light-emitting elements  13 . 
     The power control unit  30  includes a circuit board  33  and an electronic component  35  to be mounted thereon. Then, the circuit board  33  preferably allows at least part of light radiated from the light-emitting elements  13  to pass therethrough. A translucent resin substrate and a ceramic substrate may be used as the circuit board  33 , for example. A sapphire substrate or a SiC substrate may be used. The power control unit  30  is not limited to a positive circuit including a transistor and the like and, for example, may be a resistance which lowers a power source voltage so as to comply with a drive voltage of the light-emitting element  13 . 
     The power control unit  30  is electrically connected to, for example, the external terminal  40  attached to the ceramic housing  20  via a lead wire  39 . The external terminal  40  is a cap configured to engage a socket connected to the external power source. The external terminal  40  is an Edison Type E17-base cap, and includes a cylindrical shell portion  41  formed of a copper plate having a thread, and a conductive eyelet portion  45  provided via an electric insulating portion  43 . 
     As shown in  FIG. 1B , the shell portion  41  is fitted from the outside along the mounting portion  25  of the ceramic housing  20 , and fixed to the mounting portion by adhesion with an adhesive agent such as a silicone resin or epoxy resin or by means of caulking. Then, the lead wire  39  is connected to the shell portion  41  and the eyelet portion  45  and is electrically connected to the power control unit  30 . 
     In this manner, according to the embodiment, the structure of the luminaire  100  is simplified by using the ceramic housing  20 . In other words, in the housing using a metal such as aluminum, an insulative case for isolating the power control unit  30  from the housing, or an insulative joint for joining the external terminal  40  and the housing is required. In contrast, in the insulative ceramic housing  20 , the power control unit  30  and the external terminal  40  may be mounted directly, so that the number of components may be reduced to improve the production efficiency. 
     Furthermore, the luminaire  100  includes the cover  60  configured to cover the light-emitting portion  10 . The cover  60  is so-called a globe of a bulb type lamp and, for example, a resin such as polycarbonate or glass may be used. Further preferably, a translucent ceramic material may be used. For example, the cover  60  includes at least one material selected from among sapphire, translucent polycrystalline alumina ceramic (aluminum oxidative product), yttrium-aluminum-garnet (YAG), yttrium oxide (YOx) and aluminum nitride (AlN). 
     By using translucent ceramic for the cover  60 , the thermal radiation property of the luminaire  100  may be improved. 
     For example, the translucent ceramic has a higher coefficient of thermal conductivity than polycarbonate or glass, so that a larger thermal radiation from the cover  60  is achieved. 
     By using the translucent ceramic for both of the ceramic housing  20  and the cover  60 , the durability at a joint portion between the ceramic housing  20  and the cover  60  may be improved. 
     In other words, by using the same type of material or the same material for both of the ceramic housing  20  and the cover  60 , the values of the coefficients of linear thermal expansion may be brought close to each other, and a thermal stress applied to the joint portion may be reduced. For example, deterioration of the joint portion due to a heat cycle generated by turning ON and OFF repeatedly can be suppressed. 
       FIG. 2  is a schematic drawing illustrating the outline of the luminaire  100 . The substantially semispherical cover  60  is attached to one end of the ceramic housing  20  and the external terminal  40  is attached to the other end of the ceramic housing  20 . 
     Since both of the ceramic housing  20  and the cover  60  are formed of a translucent material, light L 1  radiated from the light-emitting element  13  is released to the outside through the cover  60  (L 2 ). In contrast, light L 3  reflected or scattered by the cover  60  and propagating in the direction toward the ceramic housing  20  is also released to the outside through the ceramic housing  20 . 
     The term “through the ceramic housing  20 ” includes not only the linear propagation of light shown in  FIG. 2 , but also a case of propagating in the housing while scattering and being released to the outside. 
     In this manner, by using the translucent ceramic, the light shielding by the housing may be reduced. Also, the coefficient of thermal conductivity of the translucent ceramic is lower than that of metal, but a sufficient thermal radiation is secured in comparison with resin and glass. In addition, the structure of the ceramic housing is simpler than that of a metallic housing in which insulative members such as an insulative case is arranged in the housing, and hence a joint surface between the components may be reduced. From this point of view, improvement of thermal radiation is achieved. 
     In other words, in the embodiment, by using the translucent ceramic housing  20 , the luminaire improved in both of the thermal radiation property and the light-distribution property is realized. 
       FIGS. 3A and 3B  are schematic views illustrating the ceramic housing  20  according to the embodiment.  FIG. 3A  is a plan view illustrating one of the end surfaces to which the light-emitting portion  10  is mounted, and  FIG. 3B  is a side view. 
     The ceramic housing  20  is formed into a cylindrical shape, and includes the mounting portion  23  for the light-emitting unit  10  at one end  20   a  thereof and the mounting portion  25  for the external terminal  40  at the other end  20   b  thereof. In the embodiment, the ceramic housing  20  is formed into a cylindrical shape and the diameter R 1  of the one end  20   a  is larger than the diameter R 2  of the other end  20   b.    
     The ceramic housing  20  has translucency and includes at least selected one of aluminum oxide, aluminum nitride, YAG, or yttrium oxide. 
     The thickness of the ceramic housing  20  is preferably between 0.5 mm to 3.0 mm inclusive. If the thickness is 0.5 mm or smaller, the yield of the molding process is lowered and the cost is increased. In contrast, if the thickness is increased to 3.0 mm or larger, the transmittance is lowered. A material price is increased, which increases the cost correspondingly. 
     For example, the ceramic material scatters light by grain boundary and pore (air holes) existing therein, and has a light-shielding property by impurities which absorb light. In other words, the ceramic material reduces the optical anisotropy of the material, and inhibits the scattering of light by reducing the number of pores. In addition, the light absorption may be inhibited by reducing the impurities contained in the material, whereby the transparency is improved. 
     In the embodiment, the light distribution is improved by releasing the light transmitted through the ceramic housing  20  to the outside. Therefore, the scattering of the light propagating in the interior of the ceramic housing  20  is allowed. In contrast, the light absorption of the ceramic material is preferably reduced to improve the transmittance of the ceramic housing  20 . 
     For example, the light transmittance of the ceramic housing  20  is preferably 60% or higher and 95% or lower. In order to do so, the thickness of the ceramic housing  20  is reduced in a range from 0.5 mm to 3.0 mm inclusive, or the coefficient of light absorption of the translucent ceramic material is adjusted. 
     The ceramic housing  20  includes a thick portion  53 , and the mounting portion  23  for the light-emitting portion  10  corresponds to an end surface of the thick portion  53 . Then, as shown in  FIG. 3A , the mounting portion  23  includes an opening  51 . 
     In the process of molding of the ceramic housing  20 , a cylindrical body  50  is primarily molded and, for example, the end  20   a  is cut out to form the opening  51 . 
     Subsequently, engaging members  27  are inserted into the opening  51  and is sintered as shown in  FIG. 3B . Then, the engaging members  27  are fixed to the interior of the opening  51  by contraction of the body  50  in the process of sintering. 
     The engaging members  27  are, for example, screw brackets, and engage screws for fixing the light-emitting portion  10 . The engaging members  27  fixed by the process described above are stable for a heat cycle occurring by turning the luminaire ON and OFF repeatedly, and have reliability higher than connection using an adhesive agent. 
     The end  20   a  of the ceramic housing  20  includes a frame  57  formed along the outer periphery thereof. The frame  57  engages an end of the cover  60  and fixes the cover  60  to the ceramic housing  20 . 
     Guides  55  configured to support the circuit board  33  are provided on an inner surface of the ceramic housing  20 . The guides  55  are two grooves provided on the inner surface of the ceramic housing  20 , and end portions of the circuit board  33  are inserted into the guides  55  respectively. 
       FIG. 4  is a partial cross-sectional view schematically illustrating the engaging portion which engages the light-emitting portion  10  and the ceramic housing  20 . 
     The engaging member  27  is embedded into the mounting portion  23  of the light-emitting portion  10  provided on the one end  20   a  of the ceramic housing  20 . The light-emitting portion  10  is fixed to the mounting portion  23  by the fixing members  19  which engage the engaging members  27 . 
     More specifically, the engaging member  27  is, for example, a screw bracket, and configured to fix the end of the light-emitting portion  10  with a screw, which is the fixing member  19 . As shown in  FIG. 4 , the back surface of the base  15  of the light-emitting portion  10  comes into surface contact with the mounting portion  23 , and transfer of heat from the base  15  to the ceramic housing  20  is secured. As described above, the engaging member  27  is inserted into the opening  51  provided on the ceramic housing  20 , and fixed thereto. Therefore, the reliability of the connection between the light-emitting portion  10  and the ceramic housing  20  is high, and stable thermal radiation from the light-emitting portion  10  to the ceramic housing  20  is secured. 
     As shown in  FIG. 4 , an end portion  63  of the cover  60  engages the frame  57  and is fixed by, for example, an adhesive agent. The frame  57  is provided along the outer periphery of the end  20   a  of the ceramic housing  20  and the entire circumference of the frame  57  comes into contact with the end portion  63  of the cover  60 . Accordingly, the thermal radiation from the ceramic housing  20  to the cover  60  is improved. 
       FIG. 5  is a schematic drawing illustrating an example of installation of the luminaire  100  according to the embodiment. As shown in the drawing, the luminaire  100  is mounted on a down-light type lighting apparatus  300 . The lighting apparatus  300  includes a metallic mirror portion  75  having an opening  77  at the lower end and a socket  73 . The luminaire  100  is connected to the external power source by screwing the external terminal  40  (cap) thereof into the socket  73 . 
     When the socket  73  is energized and the luminaire  100  is illuminated, light L 4  emitted from the cover  60  is reflected from the inner surface of the mirror portion  75  and illuminates downward. Since the ceramic housing  20  has a translucency, light L 5  reflected from the mirror portion  75  and propagating in the direction toward the ceramic housing  20  passes through the ceramic housing  20  and illuminates downward. 
     In this manner, the light-distribution property is improved by providing the ceramic housing  20  with translucency, and hence the lighting apparatus  300  realizes uniform illumination which does not form a shadow of the housing. 
     Although several exemplary embodiments are described above, the embodiments are shown as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in other various modes, and various omissions, replacements, and modifications may be made without departing the scope of the invention. The embodiments and the modifications are included in the scope and gist of the invention and are also included in the range of the following claims and their equivalents.