Patent Publication Number: US-2015060901-A1

Title: Light Emitting Module and Lighting Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priorities from Japanese Patent Application No. 2013-178636 filed on Aug. 29, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a light emitting module and a lighting device. 
     BACKGROUND 
     In recent years, as a lighting device, a lighting device including a power-saving light emitting element such as an LED (Light Emitting Diode) is used. The lighting device including such a light emitting element can obtain higher brightness or illuminance with lesser power consumption compared with, for example, a conventional incandescent lamp. 
     In the lighting device including the light emitting element, a plurality of kinds of light emitting elements having different light emission colors are sometimes mounted on a light emitting module. In this case, light output from the lighting device is light obtained by mixing lights respectively output from the plurality of kinds of light emitting elements mounted on the light emitting module. In other words, a light emission color of the light output from the lighting device is a color obtained by mixing light emission colors of the respective plurality of kinds of light emitting elements. 
     However, in the related art, an output balance of the lights respectively output by the plurality of kinds of light emitting elements sometimes changes. For example, when temperature characteristics or current characteristics of the light emitting elements mounted on the light emitting module are different, the balance of light outputs from the respective light emitting elements changes during adjustment of brightness corresponding to a change in a driving current or changes according to a change in an environmental temperature. 
     That is, when temperature characteristics or current characteristics of the respective plurality of kinds of light emitting elements are different, a change in light emission amounts of the light emitting elements varies according to a temperature rise. When the temperatures of the light emitting elements rise, the light emission amounts of the light emitting elements change at amounts of change different from one another. As a result, the balance of light outputs output from the light emitting modules changes. Therefore, a color temperature of light output from the light emitting module as a whole changes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of the configuration of a lighting device mounted with a light emitting module according to an embodiment; 
         FIG. 2  is a diagram showing an example of the configuration of the light emitting module according to an embodiment; 
         FIG. 3  is a diagram showing an example of electric wiring of the light emitting module according to an embodiment; 
         FIG. 4  is a conceptual diagram for explaining lights emitted by the light emitting module according to an embodiment; 
         FIG. 5  is a conceptual diagram showing an example of a change with temperature of a light amount of the light emitting module according to an embodiment; 
         FIG. 6  is a conceptual diagram showing an example of a change with temperature of a light amount of a light emitting module in a comparative example; and 
         FIG. 7  is an explanatory diagram summarizing a relation between a change in a color temperature and light emitting efficiency. 
     
    
    
     DETAILED DESCRIPTION 
     In view of the problems of the related art, it is an object of the present invention to provide a light emitting module and a lighting device that can suppress a change in an output balance of lights respectively output by a plurality of kinds of light emitting elements. 
     According to one embodiment, there is provided a light emitting module including: a blue LED, which is an example of a first light emitting element; a red LED, which is an example of a second light emitting element; a yellow phosphor, which is an example of a first phosphor; and a red phosphor, which is an example of a second phosphor. The yellow phosphor converts light emitted by the blue LED into light having a color different from a color of the light emitted by the blue LED. The red phosphor converts the light emitted by the blue LED into light having a color different from the color of the light emitted by the blue LED and the color of the light converted by the yellow phosphor. The red LED emits light having a color different from the color of the light emitted by the blue LED and the color of the light converted by the yellow phosphor. A light amount of the red LED is a light amount with which an amount of change of a color temperature of light obtained by mixing the light emitted by the blue LED, the light emitted by the red LED, the light converted by the yellow phosphor, and the light converted by the red phosphor is equal to or lower than 400 Kelvin, with respect to a change with temperature of the light emitting module. Consequently, the light emitting module can improve light emitting efficiency while suppressing the change with temperature of the color temperature equal to or lower than 400 Kelvin. 
     In the light emitting module according to the embodiment, the light amount of the read LED may be a light amount with which the amount of change of the color temperature of the light obtained by mixing the light emitted by the blue LED, the light emitted by the red LED, the light converted by the yellow phosphor, and the light converted by the red phosphor is equal to or lower than 200 Kelvin, with respect to a change with temperature of the light emitting module. Consequently, the light emitting module can improve light emitting efficiency while suppressing the change with temperature of the color temperature equal to or lower than 200 Kelvin. 
     In the light emitting module according to the embodiment, the red phosphor may convert the light emitted by the blue LED into light within a range of a peak wavelength of 600 to 660 nm. The red LED may emit light within a range of a peak wavelength of 590 to 640 nm. 
     According to another embodiment, there is provided a lighting device including: the light emitting module; and a control section, which is an example of a power control section. The control section controls electric power supplied to the light emitting module. The blue LED and the red LED in the light emitting module emit lights using in common the electric power supplied from the control section. Since it is unnecessary to separately supply different kinds of electric power to the blue LED and the red LED, it is possible to reduce the size of the light emitting module. 
     A light emitting module and a lighting device according to an embodiment are explained below with reference to the drawings. In the embodiment, components having the same functions are denoted by the same reference numerals and signs and redundant explanation of the components is omitted. The light emitting module and the lighting device explained in the embodiment are only an example and do not limit the present invention. The embodiments may be combined as appropriate to the extent that the embodiments do not contradict each other. 
     Configuration of a Lighting Device 
       FIG. 1  is a diagram showing an example of the configuration of a lighting device mounted with a light emitting module according to an embodiment. As shown in  FIG. 1 , a lighting device  1  according to this embodiment includes a light emitting module  10 , a main body  11 , a cap member  12 , an eyelet section  13 , a cover  14 , a control section  15 , an electric wire  16   a , and an electric wire  16   b . The light emitting module  10  is formed on a board  110  arranged on an upper surface  11   a  of a main body  11 . The board  110  is formed of ceramics having low heat conductivity, for example, alumina, silicon nitride, silicon oxide, or aluminum. 
     The main body  11  is formed of metal having high heat conductivity, for example, aluminum in a columnar shape substantially circular in a cross section. The cap member  12  is attached to one end of the main body  11 . The cover  14  is attached to the other end of the main body  11 . The main body  11  is formed such that the outer circumferential surface of the main body  11  forms a taper surface having a substantially conical shape, the diameter of which sequentially increases in a direction from one end toward the other end. 
     The main body  11  is formed in an external shape approximate to a silhouette of a neck section in a conventional mini-krypton bulb. On the outer circumferential surface of the main body  11 , a not-shown large number of thermal radiation fins radially projecting from one end toward the other end are integrally formed. 
     The cap member  12  is, for example, an E-type cap of an Edison type. The cap member  12  includes a cylindrical shell made of a cooper plate including a thread ridge. The cap member  12  includes a conductive eyelet section  13  provided at an apex at the lower end of the shell via an electrically insulated section. An opening section of the shell is electrically insulated from and fixed to an opening section at one end of the main body  11 . 
     An input line led out from a power input terminal of a not-shown circuit board in the control section  15  is connected to the shell and the eyelet section  13 . The cap member  12  is inserted into a socket provided in, for example, the ceiling to supply electric power, which is supplied from the commercial power supply, to the control section  15 . 
     The cover  14  is formed of, for example, milky-white polycarbonate. The cover  14  is formed in a smooth curved surface shape approximated to a silhouette of a mini-krypton bulb having an opening at one end. An opening end portion of the cover  14  is fit in and fixed to the main body  11  to cover a light emitting surface of the light emitting module  10 . A method of fixing the cover  14  to the main body  11  may be any of boning, fitting, screwing, and locking. 
     The control section  15  supplies electric power to the light emitting module  10  provided on the board  110  and controls lighting and extinction of the light emitting module  10 . The control section  15  includes a control circuit housed to be electrically insulated from the outside. The control section  15  converts an alternating-current voltage into a direct-current voltage according to the control by the control circuit and applies the converted direct-current voltage to the light emitting module  10  on the board  110 . The electric wires  16   a  and  16   b  for supplying electric power to the light emitting module  10  on the board  110  are connected to an output terminal of the control circuit of the control section  15 . 
     The electric wires  16   a  and  16   b  are led out to an opening section at the other end of the main body  11  via a not-shown through-hole and a not-shown guide groove formed in the main body  11 . Insulation coating is peeled from distal end portions of the electric wires  16   a  and  16   b . The distal end portions are connected to a below-mentioned connector  160  arranged on the board  110 . 
     In this way, the control section  15  supplies electric power, which is input via the shell and the eyelet section  13 , to the light emitting module  10  on the board  110  via the electric wires  16   a  and  16   b . The control section  15  collects the electric power, which is supplied to the light emitting module  10 , via the electric wires  16   a  and  16   b.    
     Configuration of the Light Emitting Module 
       FIG. 2  is a diagram showing an example of the configuration of the light emitting module according to this embodiment.  FIG. 2  is a top view showing an example of the configuration of the light emitting module  10  viewed from an arrow A direction in  FIG. 1 . As shown in  FIG. 2 , a plurality of blue LEDs  121  and a plurality of red LEDs  122  are arranged on an arrangement surface  110   a  of the board  110 . 
     Each of the blue LEDs  121  is a light emitting element configured to emit blue-based light having a peak wavelength within a range of, for example, 445 to 465 nm. Each of the red LEDs  122  is a light emitting element configured to emit red-based light having a peak wavelength within a range of, for example, 590 to 640 nm. 
     In  FIG. 2 , one blue LED among the plurality of blue LEDs  121  is denoted by reference numeral “ 121 ”. However, members indicated by the same white square shape are equivalent to the blue LEDs  121 . In  FIG. 2 , one red LED among the plurality of red LEDs  122  is denoted by reference numeral “ 122 ”. However, members indicated by the same black square shape are equivalent to the red LED  122 . 
     An annular blocking member  130  is arranged on the arrangement surface  110   a  of the board  110  to surround the blue LEDs  121  and the red LEDs  122 . In a recess formed by the inner surface of the blocking member  130  and the arrangement surface  110   a  of the board  110 , below-mentioned resin including a phosphor is filled. 
     As the resin, resin obtained by adding a phosphor to transparent resin having high diffusibility such as epoxy resin, urea resin, or silicone resin is used. Each of the blue LEDs  121  and the red LEDs  122  is entirely covered with the resin including such a phosphor from above. 
     The phosphor added to the resin is excited by the blue-based light emitted by the blue LED  121  and emits light having a color different from a color of the light emitted by the blue LED  121 . In this embodiment, a yellow phosphor excited by the blue-based light emitted by the blue LED  121  to emit yellow-based light (a peak wavelength is, for example, 540 to 570 nm), which is in a complementary color relation with the blue-based light, is added to the resin. 
     Consequently, the light emitting module  10  can emit white light as a whole using the blue-based light emitted by the blue LED  121  and the yellow-based light emitted by the yellow phosphor. Besides the yellow phosphor, a green phosphor excited by the light emitted by the blue LED  121  to emit green-based light may be added to the resin. 
     In this embodiment, a red phosphor excited by the blue-based light emitted by the blue LED  121  to emit red-based light (a peak wavelength is, for example, 600 to 660 nm) is further added to the resin  140 . It is possible to improve, with the red-based light emitted by the red phosphor and the red-based light emitted by the red LED  122 , color rendering properties of the white light emitted by the light emitting module  10  as a whole. 
     Wiring patterns  151  and  152  are formed on the arrangement surface  110   a  of the board  110 . The wiring patterns  151  and  152  are electric conductors printed on the board  110 . One end of the wiring pattern  151  and one end of the wiring pattern  152  are connected to the connector  160  provided on the board  110 . 
     As shown in  FIG. 2 , the other end of the wiring pattern  151  and the other end of the wiring pattern  152  are formed in substantially parallel linear shapes on the arrangement surface  110   a  of the board  110 . 
       FIG. 3  is a diagram showing an example of electric wiring of the light emitting module according to this embodiment. As shown in  FIG. 3 , the plurality of blue LEDs  121  and the plurality of red LEDs  122  are arranged in each of a plurality of regions  18   a  to  18   c  (in the example shown in  FIG. 3 , three regions) on the board  110 . In each of the regions  18   a  to  18   c , the plurality of blue LEDs  121  and the plurality of red LEDs  122  are connected in series by a bonding wire  172 . 
     In each of the regions  18   a  to  18   c , one end of the plurality of blue LEDs  121  and the plurality of red LEDs  122  connected in series is connected to the other end of the wiring pattern  151 , which is formed in a linear shape, by a bonding wire  171 . The other end of the plurality of blue LEDs  121  and the plurality of red LEDs  122  connected in series is connected to the other end of the wiring pattern  152 , which is formed in a linear shape, by the boding wire  171 . 
     In each of the regions  18   a  to  18   c , as shown in  FIG. 3 , the plurality of blue LEDs  121  and the plurality of red LEDs  122  connected in series are arranged to meander from the wiring pattern  151  to the wiring pattern  152  while being folded back at every predetermined number (in the example shown in  FIG. 3 , at every three LEDs) along a linear portion of the wiring pattern  151 . 
     Electric power supplied to the wiring pattern  151  and electric power supplied to the wiring pattern  152  from the control section  15  via the connector  160  are respectively supplied in common to the plurality of blue LEDs  121  and the plurality of red LEDs  122  connected in series in each of the regions  18   a  to  18   c.    
       FIG. 4  is a conceptual diagram for explaining light emitted by the light emitting module according to this embodiment. The resin  140  includes a yellow phosphor  141  and a red phosphor  142 . The blue LED  121  emits blue-based light. The yellow phosphor  141  is excited by the light of the blue LED  121  to emit yellow-based light. The light emitting module  10  emits while light as a whole using the blue-based light emitted by the blue LED  121  and the yellow-based light emitted by the yellow phosphor  141 . 
     The red phosphor  142  is excited by the light of the blue LED  121  to emit red-based light. The red LED  122  emits red-based light. The light emitting module  10  can improve color rendering properties of white light with these red-based lights. 
     The red phosphor  142  absorbs the light of the blue LED  121  and emits a part of the light as red-based light. Therefore, when the red-based light is generated by the blue LED  121  and the red phosphor  142 , a conversion loss occurs. The red phosphor  142  is excited by the light of the blue LED  121  to further absorb yellow-based light emitted by the yellow phosphor  141  and emit a part of the yellow-based light as red-based light. A conversion loss also occurs in that case. 
     If all red-based lights are generated by the red LED  122 , the conversion loss due to the red phosphor  142  does not occur and higher light emitting efficiency is obtained. However, since a change with temperature of a light amount of the red LED  122  is large, in the light emitting module  10  in this embodiment, a generation amount of red-based lights is shared by the red phosphor  142  and the red LED  122 . 
       FIG. 5  is a conceptual diagram showing an example of a change with temperature of a light amount of the light emitting module in this embodiment. In  FIG. 5 , “B” indicates a change with temperature of a light amount of blue-based light emitted by the blue LED  121 . “Y” indicates a change with temperature of a light amount of yellow-based light emitted by the yellow phosphor  141  by being excited by the light of the blue LED  121 . 
     “R 1 ” indicates a change with temperature of a light amount of red-based light emitted by the red LED  122 . “R 2 ” indicates a change with temperature of a light amount of red-based light emitted by the red phosphor  142  by being excited by the light of the blue LED  121 . “R” indicates a change with temperature of a light amount obtained by combining “R 1 ” and “R 2 ”. 
     In the blue LED  121  and the red LED  122 , for example, as indicated by “B” and “R 1 ” in  FIG. 5 , the light amounts decrease according to a rise of temperature. An amount of decrease in the light amount involved in the temperature rise is larger in the red LED  122  than the blue LED  121 . As indicated by “Y” and “R 2 ” in  FIG. 5 , light amounts of yellow-based and red-based lights emitted by the yellow phosphor  141  and the red phosphor  142  by being excited by light of the blue LED  121  show temperature changes substantially the same as the change with temperature of the light amount of the blue LED  121 . 
     When the lighting device  1  is lit, the temperature of the light emitting module  10  rises to a certain degree according to heat generation of the blue LED  121  and the red LED  122 . The temperature stabilizes in an equilibrium state of heat generation and heat radiation. The temperature of the light emitting module  10  during the lighting (e.g., “X” in  FIG. 5 ) and the temperature of the light emitting module  10  in a stable state after the lighting (e.g., “X′” in  FIG. 5 ) are different by about several ten ° C. 
     Since change amounts of the light amounts with respect to the temperature change are different in the blue LED  121  and the red LED  122 , if the balance of light amounts of lights having the colors emitted by the light emitting module  10  is designed such that a color temperature is a predetermined color temperature in the stable state, a color temperature of light emitted by the light emitting module  10  during the lighting is different from a design value. 
     If red-based light is generated by only the red LED  122 , a relation between an amount of light emitted by the light emitting module  10  and temperature is, for example, as shown in  FIG. 6 .  FIG. 6  is a conceptual diagram showing an example of a change with temperature of a light amount of a light emitting module in a comparative example. In  FIG. 6 , “R” indicates a change with temperature of a light amount of red-based light emitted by the red LED  122 . If the red-based light is generated by only the red LED  122 , a light amount necessary for improving color rendering properties of light emitted by the light emitting module  10  as a whole is covered by the red-based light emitted by the red LED  122 . 
     If an amount of the light emitted by the red LED  122  is designed such that a color temperature of light of the light emitting module  10  at the temperature in the stable state (“X′” in  FIG. 6 ) is a predetermined color temperature, at the temperature of the light emitting module  10  during the lighting (“X” in  FIG. 6 ), an amount of light emitted by the red LED  122  is extremely large compared with amounts of lights emitted by the blue LED  121  and the yellow phosphor  141 . 
     Therefore, during the lighting, the balance of amounts of lights having the colors emitted by the light emitting module  10  as a whole greatly deviates from the design value. Consequently, a color temperature of the light emitted by the light emitting module  10  is greatly different during the lighting and in the stable state. In particular, an amount of light emitted by the red LED  122  during the lighting is large compared with amounts of other lights. Therefore, the light emitted by the light emitting module  10  during the lighting is reddish white light having a color temperature lower than the design value. 
     It is also conceivable to generate red-based light with the blue LED  121  and the red phosphor  142  without using the red LED  122  having the large change with temperature of the light amount. However, when a conversion loss that occurs when the red phosphor  142  converts light emitted by the blue LED  121  into red-based light and a conversion loss that occurs when the red phosphor  142  further converts light converted by the yellow phosphor  141  are taken into account, it is possible to improve the light emitting efficiency of the light emitting module  10  when red-based light is generated using the red LED  122 . Therefore, it is undesirable to generate red-based light only with a combination of the blue LED  121  and the red phosphor  142 . 
     Therefore, in the light emitting module  10  according to this embodiment, red-based light is generated by combining the red LED  122  having high light emitting efficiency and the red phosphor  142  that shows a temperature change close to the temperature change of the light amount of the blue LED  121 . Consequently, for example, as it is apparent from  FIG. 5 , it is possible to suppress, compared with the comparative example shown in  FIG. 6 , the deviation of the balance between an amount of red-based light and amounts of blue-based and yellow-based lights during the lighting and in the stable state. 
     Consequently, it is possible to suppress a change in a color temperature of white light emitted by the light emitting module  10  during the lighting and in the stable state. Compared with the generation of red-based light only by the combination of the blue LED  121  and the red phosphor  142 , the light emitting module  10  can improve light emitting efficiency. 
       FIG. 7  is an explanatory diagram summarizing an example of a relation between a change in a color temperature and light emitting efficiency. The above explanation is summarized as shown in  FIG. 7 . When blue-based light is generated by the blue LED  121 , yellow-based light is generated by the yellow phosphor  141 , and red-based light is generated by the red phosphor  142 , for example, as shown in an upper stage of  FIG. 7 , a temperature change of a color temperature of light emitted by the light emitting module  10  as a whole is small (e.g., about 20 Kelvin). However, in this case, the light emitting efficiency of the light emitting module  10  is deteriorated by a conversion loss, re-absorption, and the like by the red phosphor  142 . 
     When blue-based light is generated by the blue LED  121 , yellow-based light is generated by the yellow phosphor  141 , and red-based light is generated by the red LED  122 , for example, as shown in a middle stage of  FIG. 7 , a temperature change of a color temperature of light generated by the light emitting module  10  as a whole is large (e.g., about 400 Kelvin). 
     However, in this case, since the red phosphor  142  is not used, the light emitting efficiency of the light emitting module  10  is relatively high. For example, when the light emitting efficiency of the light emitting module  10  in the configuration in the upper stage in which the blue LED  121 , the yellow phosphor  141 , and the red phosphor  142  are used is represented as 100%, light emitting efficiency in the configuration in the middle stage in which the blue LED  121 , the yellow phosphor  141 , and the red LED  122  are used is, for example, about 120%. 
     On the other hand, in this embodiment in which blue-based light is generated by the blue LED  121 , yellow-based light is generated by the yellow phosphor  141 , red-based light is generated by the red phosphor  142 , and red-based light is generated by the red LED  122 , for example, as shown in a lower stage of  FIG. 7 , it is possible to suppress a change with temperature of a color temperature of light generated by the light emitting module  10  as a whole to a medium degree (e.g., about 200 Kelvin). 
     In this case, since an amount of the red phosphor  142  can be reduced, it is possible to suppress deterioration in the light emitting efficiency of the light emitting module  10 . For example, when the light emitting efficiency of the light emitting module  10  in the configuration in the upper stage in which the blue LED  121 , the yellow phosphor  141 , and the red phosphor  142  are used is represented as 100%, light emitting efficiency in the configuration in this embodiment in which the blue LED  121 , the yellow phosphor  141 , the red phosphor  142 , and the red LED  122  are used is, for example, about 110%. 
     In the light emitting module  10  in this embodiment, the number of red LEDs  122 , the sizes of the respective red LEDs  122 , and the like are designed such that a light amount of the red LED  122  is a predetermined light amount. The predetermined light amount is a light amount with which an amount of change of a color temperature of light obtained by mixing light emitted by the blue LED  121 , light converted by the yellow phosphor  141 , light converted by the red phosphor  142 , and light emitted by the red LED  122  is equal to or lower than 400 Kelvin, with respect to a change with temperature of the light emitting module  10 . 
     In the light emitting module  10  in this embodiment, the predetermined light amount is more preferably a light amount with which an amount of change of a color temperature of light obtained by mixing light emitted by the blue LED  121 , light converted by the yellow phosphor  141 , light converted by the red phosphor  142 , and light emitted by the red LED  122  is equal to or lower than 200 Kelvin, with respect to a change with temperature of the light emitting module  10 . 
     As explained above, as the light emitting module  10  in this embodiment, it is possible to provide the light emitting module  10  having high light emitting efficiency while keeping a change with temperature of a color temperature within an allowable range by increasing an amount of light emitted by red LED  122  within a range in which the change with temperature of the color is within the allowable range. 
     In the light emitting module  10  in this embodiment, a light amount of the red LED  122  is designed such that a temperature change of a color temperature of light emitted by the light emitting module  10  as a whole is within 400 Kelvin. Consequently, to set a temperature change of a color temperature of white light emitted by the light emitting module  10  within 400 Kelvin, it is unnecessary to separately control electric power supplied to the blue LED  121  and electric power supplied to the red LED  122 . Therefore, it is possible to reduce the size of the control section  15  configured to supply electric power to the light emitting module  10 . Consequently, it is possible to reduce the size of the lighting device  1 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.