Patent Publication Number: US-2012025221-A1

Title: Light Emitting Device

Description:
TECHNICAL FIELD 
     The present invention relates to a light emitting device having a light emitting element such as a light emitting diode, 
     BACKGROUND ART  
     In recent years, in place of conventional light emitting devices such as fluorescent lamps or incandescent lamps, light emitting devices have been developed which include a light source having a light emitting element such as a light emitting diode. Light emitting devices including a light emitting element are anticipated from the point of view of power consumption and product lifetime in comparison to conventional light emitting devices. 
     SUMMARY OF INVENTION 
     In light emitting devices including a light emitting element, the size of a light source is smaller than that of conventional light emitting devices, and thus a light intensity distribution is required to be improved. 
     According to an aspect of the invention, a light emitting device includes a plurality of light sources each including a light emitting element, a first light reflective member which surrounds the plurality of light sources, and a second light reflective member disposed ahead of the first light reflective member in a light radiation direction of the plurality of light sources with reference to the plurality of light sources. The second light reflective member includes a light transmitting material. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a perspective view of a light emitting device according to a first embodiment of the invention; 
         FIG. 2  shows a perspective view of a light emitting unit  90  shown in  FIG. 1 ; 
         FIG. 3  shows a vertical section view taken along the line A-A of the light emitting unit shown in  FIG. 2 ; 
         FIG. 4  shows a vertical section view of an exemplary light emitting unit  1 ; 
         FIG. 5  shows a vertical section view of another exemplary light emitting unit  1 ; 
         FIG. 6  shows a section view partially of a light source  12 ; 
         FIG. 7  schematically shows alight intensity distribution of the light emitting unit  90 ; 
         FIG. 8  schematically shows a light intensity distribution of the another light source unit  1 ; 
         FIG. 9  schematically shows how light propagates from a light source unit  90  in a light emitting device according to a second embodiment of the invention; 
         FIG. 10  schematically shows how light propagates from a light source unit  90  in a light emitting device according to a third embodiment of the invention; and 
         FIG. 11  schematically shows how light propagates from a light source unit  90  in a light emitting device according to a fourth embodiment of the invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Now referring to the drawings, exemplary embodiments of the invention are described below. 
     First Embodiment 
     A light emitting device according to a first embodiment of the invention will be described with reference to  FIG. 1 . The light emitting device includes a power source unit  80  and a light emitting unit  90  electrically connected to the power source unit  80 . In  FIG. 1 , the light emitting device is disposed in an imaginary xyz space. An upper direction in  FIG. 1  indicates a positive direction of an imaginary z axis. 
     As shown in  FIGS. 2 and 3 , the light emitting unit  90  includes a light source unit  1  and a light reflective member  2 . In  FIG. 3 , an internal structure of the light emitting unit  90  is partially omitted. 
     As shown in  FIG. 4 , an exemplary light source unit  1  includes a mounting substrate  11 , a plurality of light sources  12  disposed on the mounting substrate  11 , and a light reflective member  13  disposed on the mounting substrate  11 . The light reflective member  13  has a plurality of light reflective surfaces  131  which are disposed corresponding to the plurality of light sources  12 . The light reflective surfaces  131  surround the light sources  12  and have, for example, a paraboloid shape. The light reflective surfaces  131  reflect light radiated from the light sources  12  in a negative direction of the imaginary z axis. 
     As shown in  FIG. 5 , another exemplary light source unit  1  further includes a light reflective member  14  which is disposed ahead of the light reflective member  13  in a light radiation direction of the light sources  12  with reference to the light sources  12 . In  FIG. 5 , the “light radiation direction of the light sources  12 ” indicates the negative direction of the imaginary z axis. The light reflective member  2  includes a light transmitting material. The “light transmitting property” of the light reflective member  2  means that at least some of light rays radiated from the light source  12  can pass through the light reflective member. Examples of the light transmitting material include polymethylmethacrylate (PMMA), acrylic resin, polybutylene terephthalate, polypropylene, acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS resin), polycarbonate, polyester, polyethylene and epoxy resin. 
     As shown in  FIG. 6 , the light source  12  includes a package  121 , a light emitting element  124  mounted on the package  121 , a light transmitting member  125  enclosing the light emitting element  124 , and a wavelength conversion member  126  disposed on or above the light transmitting member  125 . An upper direction in  FIG. 6  indicates the negative direction of the imaginary z axis. 
     The package  121  includes a base  122  and a frame member  123  disposed on the base  122 . The frame member  123  surrounds the light emitting element  124 . 
     The light emitting element  124  is, for example, a semiconductor device such as a light emitting diode (LED) and radiates primary light in response to driving power. 
     The light transmitting member  125  is disposed inside the frame member  123  and covers the light emitting element  124 . The “light transmitting property” of the member  125  means that a wavelength of at least some of light rays radiated from the light emitting element  124  can pass through the light transmitting member. The light transmitting member  125  includes, for example, a silicone resin. 
     The wavelength conversion member  126  covers the light transmitting member  125  and is fixed to the frame member  123 . The wavelength conversion member  126  includes a plurality of fluorescent particles which radiate secondary light in response to the primary light, and a light transmitting resin. The plurality of fluorescent particles are contained in the light transmitting resin. The “light transmitting property” of the resin means that a wavelength of at least some of light rays radiated from the light emitting element  124  and a wavelength of at least some of light rays radiated from the plurality of fluorescent particles can pass through the light transmitting resin. 
     As described above, an example of the light source  12  is a light emitting diode lamp (LED lamp). Another example of the light source  12  is an organic electroluminescence (organic EL). 
     Referring to  FIGS. 2 and 3  again, the light reflective member  2  is disposed ahead of the light reflective member  13  in the light radiation direction of the plurality of light sources  12  with reference to the plurality of light sources  12 . In  FIGS. 2 and 3 , the “light radiation direction of the plurality of light sources  12 ” indicates the negative direction of the imaginary z axis. That is, the light radiation direction of the plurality of light sources  12  indicates a downstream side in a light emission direction of the light emitting device. 
     The light reflective member  2  includes a light transmitting material. The “light transmitting property” of the light reflective member  2  means that at least some of light rays radiated from the light source  12  can pass through the light reflective member. Examples of the light transmitting material include polymethylmethacrylate (PMMA), acrylic resin, polybutylene terephthalate, polypropylene, acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS resin), polycarbonate, polyester, polyethylene and epoxy resin. 
     The light reflective member  2  surrounds the plurality of light sources  12 . To “surround the plurality of light sources  12 ” includes not only a structure in which each of the plurality of light sources  12  is surrounded by the light reflective surface  131 , as shown in  FIG. 4 , but also a structure in which the plurality of light sources  12  are surrounded by one light reflective surface  131 . 
     As schematically shown in  FIG. 7 , some light rays  120   a  radiated from the light source  12  are reflected by the light reflective member  2  and propagate in the negative direction of the imaginary z axis. A light intensity distribution  901  is formed by the light rays  120   a  and the like. Other light rays  120   b  radiated from the light source  12  pass through the light reflective member  2  and propagate in the negative direction of the imaginary z axis since the light reflective member  2  includes a light transmitting material. A light intensity distribution  902  is formed by the light rays  120   b  and the like. 
     Since the light emitting device of this embodiment is provided with the light reflective member  2  including the light transmitting material, the light emitting device has a light intensity distribution  900  including the distribution  902 . Accordingly, the light emitting device of this embodiment has an appropriate level of light spread and can realize, for example, a pleasant illumination space. 
     As schematically shown in  FIG. 8 , in another exemplary light source unit  1 , some light rays  120   c  radiated from the light source  12  are reflected by the light reflective member  14  and propagate in the negative direction of the imaginary z axis. A light intensity distribution  101  is formed by the light rays  120   c  and the like. Other light rays  120   d  radiated from the light source  12  pass through the light reflective member  14  and propagate in the negative direction of the imaginary z axis since the light reflective member  14  includes a light transmitting material. A light intensity distribution  102  is formed by the light rays  120   d  and the like. Due to the overlap of the light intensity distributions  102  of the neighboring light sources  12 , another exemplary light source unit  1  can have a continuous light intensity distribution. Accordingly, in another exemplary light source unit  1 , unevenness in the light intensity distribution is reduced. 
     Second Embodiment 
     A second embodiment of the invention will be described with reference to  FIG. 9 . A configuration of a light emitting device of the second embodiment that is different from that of the light emitting device of the first embodiment is a configuration of the light reflective member  2 . In other respects, the configuration is the same as in the light emitting device of the first embodiment. 
     The light reflective member  2  of the second embodiment has an internal surface having a rougher surface texture than that of the light reflective surface  131  of the light reflective member  13 . The “rougher surface texture than that of the light reflective surface  131 ” means that the internal surface has higher arithmetic mean roughness Ra than that of the light reflective surface  131 . The exemplary arithmetic mean roughness Ra of the internal surface of the light reflective member  2  is in the range of 0.1 μm to 30 μm. The exemplary arithmetic mean roughness Ra of the light reflective surface  131  is in the range of 0.001 μm to 0.1 μm. 
     Some light rays  120   a  radiated from the light source  12  are reflected to be scattered in the internal surface of the light reflective member  2 . The light emitting device of the second embodiment can properly scatter some light rays  120   a  radiated from the light source  12 . Accordingly, the light emitting device of the second embodiment has an improved light intensity distribution. 
     Third Embodiment 
     A third embodiment of the invention will be described with reference to  FIG. 10 . A configuration of a light emitting device of the second embodiment that is different from that of the light emitting device of the first embodiment is a configuration of a second light reflective member  3 . In other respects, the configuration is the same as in the light emitting device of the first embodiment. 
     The light reflective member  2  of the second embodiment has an external surface having a rougher surface texture than that of the light reflective surface  131 . The “rougher surface texture than that of the light reflective surface  131 ” means that the external surface has higher arithmetic mean roughness Ra than that of the light reflective surface  131 . The exemplary arithmetic mean roughness Ra of the external surface of the light reflective member  2  is in the range of 0.1 μm to 30 μm. The exemplary arithmetic mean roughness Ra of the light reflective surface  131  is in the range of 0.001 μm to 0.1 μm. 
     Some light rays  120   b  radiated from the light source  12  pass through the light reflective member  2  so as to be scattered by the external surface of the light reflective member  2 . The light emitting device of the second embodiment can properly scatter light rays  120   b  radiated from the light source  12 . Accordingly, the light emitting device of the second embodiment has an improved light intensity distribution. 
     Fourth Embodiment 
     A fourth embodiment of the invention will be described with reference to  FIG. 11 . A configuration of a light emitting device of the fourth embodiment that is different from that of the light emitting device of the first embodiment is a configuration of the light reflective member  2 . In other respects, the configuration is the same as in the light emitting device of the first embodiment. 
     The light reflective member  2  of the fourth embodiment includes a plurality of light scattering particles. The “light scattering property” of the particles means that the propagation direction of the light radiated from the light source  12  is changed by reflection or light refraction. Some light rays  120   b  radiated from the light source  12  are reflected or refracted by the light scattering particles in the light reflective member  2 . Examples of the material for the light scattering particles include metallic oxide particles such as aluminum oxide, zirconium oxide, titanium oxide and yttrium oxide, glass particles having a refractive index different from that of the second light reflective member  3 , polymethylmethacrylate (PMMA), acryl, polybutylene terephthalate, polypropylene, acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS resin), polycarbonate, polyester, polyethylene and epoxy resin which have a light transmitting property. The light emitting device of the fourth embodiment can properly scatter the light radiated from the light source  12 . Accordingly, the light emitting device of another embodiment has an improved light intensity distribution.