Patent Application
20130170208
The present disclosure relates to light emitting devices and surface light source devices, and more particularly to a light emitting device including a reflector configured to reflect light emitted sideways from a light-emitting element.
There is a known light emitting device in which a reflector for reflecting light emitted sideways from a light-emitting element to a direction immediately upward from the light-emitting element is disposed around the immediately above in order to utilize the light from the light-emitting element efficiently. To utilize light more efficiently, proposed is a configuration in which a plurality of inverted conical reflectors are concentrically arranged about a light-emitting element has been investigated in order to enhance the efficiency of utilizing light (see, for example, Patent Document 1).
Multiple reflectors are expected to be able to increase the number of reflections to enhance emission intensity above the light-emitting element.
The above conventional light emitting device, however, has the following drawbacks. The conventional light emitting device is intended to scatter light by means of repetitive reflections of light among the reflectors. To achieve this, the reflectors are located above the light-emitting element to allow light to enter from below the reflectors. In the configuration in which reflectors are located above the light-emitting element, light emitted diagonally upward from the light-emitting element is reflected by the reflectors, but light emitted immediately upward from the light-emitting element passes among the reflectors and does not contribute to enhancement of the light emission efficiency. In addition, the reflectors located above the light-emitting element disadvantageously blocks light emitted from the light-emitting element.
It is therefore an object of the present invention to provide a light-emitting device with high light emission efficiency in which light emitted from a light-emitting element can be efficiently guided upward.
To achieve the object, a light emitting device according to the present disclosure includes a plurality of reflectors concentrically surrounding a light-emitting element, where upper ends of the reflective surfaces are located higher with increasing distance from the light-emitting element.
Specifically, a light emitting device according to the present disclosure includes: a board; and a light-emitting element fixed onto the board and having a light emission region that faces upward, wherein the board includes a plurality of projections spaced from one another and each surrounding the light-emitting element, a side surface of each of the projections facing the light-emitting element is a reflective surface that reflects light emitted sideways from the light emission region, the reflective surfaces of the projections are concentric about the light-emitting element, and upper ends of the reflective surfaces are located higher with increasing distance from the light-emitting element.
A light emitting device according to the present disclosure can be achieved as a light emitting device in which light emitted from a light-emitting element can be efficiently guided upward to have a high emission efficiency.
a)-3(c) illustrate a light emitting device according to the embodiment,
a) and 4(b) illustrate an example of a lead frame,
a)-5(c) illustrate the light emitting device of the embodiment except for a light-control lens,
a) and 6(b) illustrate an example of a lead frame assembly,
An example light emitting device includes light emitting device, includes: a board; and a light-emitting element fixed onto the board and having a light emission region that faces upward, wherein the board includes a plurality of projections spaced from one another and each surrounding the light-emitting element, a side surface of each of the projections facing the light-emitting element is a reflective surface that reflects light emitted sideways from the light emission region, the reflective surfaces of the projections are concentric about the light-emitting element, and upper ends of the reflective surfaces are located higher with increasing distance from the light-emitting element.
The example light emitting device can cause light emitted obliquely upward from the side of the light-emitting element to be reflected on the reflective surfaces. In addition, since upper ends of the reflective surfaces are located higher with increasing distance from the light-emitting element, light not reflected on an inner one of the reflective surfaces but travelling straight can be reflected on an outer one of the reflective surfaces. Thus, light can be emitted efficiently upward.
In the light emitting device, the reflective surfaces may be sloped at larger angles with increasing distance from the light-emitting element. In this configuration, the reflection angles of the reflective surfaces decrease with increasing distance from the light-emitting element, thereby efficiently collecting light from the light-emitting element to the direction immediately above the light-emitting element.
The light emitting device may further include a light-control lens having an axis that coincides with an optical axis of the light emission region, wherein the light-control lens my include a recess that is located around the optical axis and having a diameter that is larger in a bottom than in an upper end, and at least one of the reflective surfaces may be located immediately under the recess. In this configuration, light collected to the direction immediately above the light-emitting element can be dispersed by the light-control lens, thereby irradiating a wide range.
In the light emitting device, at least part of a wall surface of the recess may be a reflective surface that reflects light reflected on the at least one of the reflective surface located immediately under the recess in a direction away from the optical axis. In this configuration, variations in luminance, i.e., a phenomenon in which the luminance is higher in a region immediately above the light-emitting element with a high emission intensity than in its periphery, can be reduced.
An example surface light source device includes a plurality of light emitting devices described above, wherein the plurality of light emitting devices are arranged to have a lattice pattern. This configuration can provide a surface light source device capable of uniformly irradiating a wide range.
As illustrated in
The light-control member 20 includes a diffuser plate 21, a diffuser sheet 22, a first light-control sheet 23, and a second light-control sheet 24.
The diffuser plate 21 can be, for example, a resin plate having a coarse surface similar to frosted glass in order to diffuse light from the surface light source part 30. The diffuser plate 21 can be made of, for example, a polycarbonate (PC) resin, a polyester (PS) resin, or a cyclic olefin polymer (COP) resin.
The diffuser sheet 22 is provided to further diffuse light diffused by the diffuser plate 21, and can be made of a resin sheet of, for example, polyester.
The first light-control sheet 23 collects light diffused by the diffuser plate 21 and the diffuser sheet 22, and directs the collected light toward the liquid crystal panel D. The first light-control sheet 23 is a sheet having a prism surface. Specifically, the first light-control sheet 23 can be made of, for example, a polyester resin provided with triangular strips (i.e., linearly extending triangular projections) of an acrylic resin. The prism surface with the triangular strips can have a sawtooth profile in cross section. The second light-control sheet 24 collects light that has not been collected by the first light-control sheet 23. The second light-control sheet 24 reflects S waves toward the surface light source part 30 to increase the proportion of P waves that pass through the liquid crystal panel D, thereby increasing the accumulated light amount to increase the luminance. In this manner, the first light-control sheet 23 and the second light-control sheet 24 can reduce unevenness of brightness.
As illustrated in
A configuration of the light emitting devices 32 of this embodiment will now be described in detail. As illustrated in
In this embodiment, the light-emitting element 110 has a substantially rectangular solid shape, and the upper surface of the light-emitting element 110 is substantially rectangular in plan view. The light-emitting element 110 can be, for example, a blue light-emitting diode. In general, the light-emitting element 110 includes a semiconductor layer and an electrode formed on a substrate. The semiconductor layer includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, which are stacked in this order on the substrate. The electrode includes a p-side electrode in contact with the p-type semiconductor layer and an n-side electrode in contact with the n-type semiconductor layer. In this embodiment, the n-side electrode is formed on the n-type semiconductor layer exposed by etching the p-type semiconductor layer, the light-emitting layer, and part of the n-type semiconductor layer. In this embodiment, the p-side electrode and the n-side electrode are located at the opposed longer sides with the light emission region sandwiched therebetween. The light-emitting element 110 serves as a point light source that emits light from the light emission region by applying a voltage across the p-side electrode and the n-side electrode. The light emission region is actually a surface with a predetermined size, but is a very small region and thus, when being seen as a light emitting device 32, can be regarded as a point.
The light-control lens 114 is made of a silicon-based resin, and diffuses light emitted from the light-emitting element 110 to a wide range. The light-control lens 114 includes a substantially hemispherical lens portion 141 and a brim portion 142 located around the periphery of the lens portion 141 and having a square outer shape.
The lens portion 141 has a recess 141a around the optical axis L. In the recess 141a, the diameter at the upper end is larger than the diameter at the bottom, and the slope of the wall gradually becomes gentle from the bottom to the upper end.
The recess 141a is surrounded by a horizontal surface 141b that is substantially horizontal (i.e., substantially orthogonal to the optical axis L). The horizontal surface 141b is surrounded by an arc surface 141c that is a gently convex surface. The arc surface 141c is surrounded by a peripheral surface 141d that is substantially vertical. A bottom portion 141e having a gently concave curve is provided between the peripheral surface 141d and the brim portion 142. The peripheral surface 141d is partially cut out in the vertical direction, thereby forming flat portions 141f. The flat portions 141f are opposed to each other with the optical axis L sandwiched therebetween. The flat portions 141f are opposed to the longer sides of the light-emitting element 110. The flat portions 141f are slightly sloped toward the optical axis L from the bottom to the top thereof. In this embodiment, each of the flat portions 141f is sloped at about 2° with respect to the optical axis L.
The board 112 has a lead frame 121 and a resin frame 122. The lead frame 121 may be a copper alloy plate obtained by patterning laminated plating layers of, for example, nickel or gold. As illustrated in
As illustrated in
As illustrated in
As illustrated in
A first opening 122a, which is circular in plan view, for exposing the die bonding part 123A of the lead frame 121 therein is formed at the center of the resin frame 122. The first opening 122a is formed to have its diameter gradually increase from the lower end to the upper end, and the wall of the first opening 122a is sloped. The first opening 122a is surrounded by a first projection 125 having a square shape in plan view. Accordingly, the wall of the first opening 122a is integrated with a side surface (i.e., the inner side surface) of the first projection 125 facing the first opening 122a to form a first reflective surface 125A that upward reflects part of light emitted from the light-emitting element 110 fixed to the die bonding part 123A. That is, the first opening 122a and the first projection 125 serve as a first reflector. The outer side surface of the first projection 125 has a slope such that the height of the first projection 125 gradually decreases. The first reflector is located immediately under the recess 141a formed in the light-control lens 114.
A second projection 126 having a circular shape in plan view and surrounding the light-emitting element 110 is provided outside the first projection 125. The inner side surface of the second projection 126 serves as a second reflective surface 126A, so that the second projection 126 serves as a second reflector. The second reflective surface 126A is sloped at an angle larger than the first reflective surface 125A. The second reflector reflects, for example, light not reflected by the first reflector and light reflected on the light-control lens 114 toward the board 112.
The first reflective surface 125A and the second reflective surface 126A are formed concentrically about the light-emitting element 110. The upper end of the second reflective surface 126A is located at a level higher than the upper end of the first reflective surface 125A.
The outer side surface of the second projection 126 is partially cut out such that a straight portion 126B is formed. The straight portion 126B serves as a polarity indicator for enabling visual recognition of orientation of the electrodes of the light emitting device 32.
Between the first projection 125 and the second projection 126, a second opening 122b, a third opening 122c, a fourth opening 122d, and a fifth opening 122e for exposing the wire bonding part 123B, the protection-device die bonding part 123C, the wire bonding part 124A, and the protection-device wire bonding part 124B, respectively, are formed.
The p-side electrode of the light-emitting element 110 fixed to the die bonding part 123A exposed in the first opening 122a is connected to the wire bonding part 123B exposed in the second opening 122b by the wire 116. The n-side electrode of the light-emitting element 110 is connected to the wire bonding part 124A exposed in the fourth opening 122d by the wire 116. An electrode of the protection device fixed to the protection-device die bonding part 123C exposed in the third opening 122c is connected to the protection-device wire bonding part 124B exposed in the fifth opening 122e by a wire 118. The wires 116 and 118 may be, for example, gold (Au) fine wires.
An encapsulating resin is embedded in a region surrounded by the first projection 125, and a resin encapsulating part 127 encapsulating the light-emitting element 110 fixed to the die bonding part 123A is formed. The resin encapsulating part 127 includes a first encapsulating part 127A of, for example, a transparent silicone resin and a second encapsulating part 127B of, for example, a silicone resin containing a phosphor. The upper surface of the second encapsulating part 127B is in contact with the wires 116 connecting the p-side electrode and the n-side electrode of the light-emitting element 110 to the wire bonding part 123B and the wire bonding part 124A, respectively. Accordingly, the second encapsulating part 127B has its thickness gradually increase from the outer rim toward the center thereof in accordance with the shape of the wires 116.
The presence of the second encapsulating part 127B containing a phosphor can convert light emitted from the light-emitting element 110 to light with another wavelength. For example, in a case where the light-emitting element 110 emits blue light, the use of a phosphor that is excited by blue light and emits yellow light as light of a complementary color can obtain white light as a mixture of the blue light and the yellow light. In this case, the phosphor can be, for example, a silicate phosphor or an yttrium aluminium garnet (YAG)-based phosphor.
The light emitting device of this embodiment is configured such that the first encapsulating part 127A containing no phosphor covers the light-emitting element 110 except for the upper surface thereof. Accordingly, even when light emitted sideways from the light-emitting element 110 is reflected by the first reflector and the second reflector to travel a distance longer than light emitted upward, excessive conversion and attenuation of the wavelength caused by a phosphor are not likely to occur.
The protection device 117 constitutes a protection circuit for protecting the light-emitting element 110 against overvoltage. In this embodiment, the protection device 117 is a Zener diode, but may be a diode, a capacitor, a resistor, or a varistor, for example. When the light-emitting element 110 has a sufficiently high breakdown voltage, the protection device 117 is not necessarily provided.
An example of a method for fabricating a light emitting device 32 will now be described. First, as illustrated in
Next, the lead frame assembly 161 is clamped with a mold, and resin frames 122 are molded by transfer molding.
Then, light-emitting elements 110 are fixed (die-bonded) to die bonding parts 123A of anode frames 121A. In addition, protection devices 117 are fixed to protection-device die bonding parts 123C, and the protection devices 117 are connected to protection-device wire bonding parts 124B by wires 118.
Thereafter, as illustrated in
The above-described arrangement of the wires 116 can prevent an encapsulating resin from flowing out of a region surrounded by the first projection 125 in potting the encapsulating resin, and can keep the encapsulating resin raised. In
This arrangement can allow the wires 116 to be bonded at positions close to the first projection 125. Accordingly, the size of the device can be reduced, and the length of the wires 116 can also be reduced.
Subsequently, a first encapsulating resin of, for example, a transparent liquid silicone resin is potted into a region surrounded by the first projection 125, and then cured, thereby forming a first encapsulating part 127A. In potting the first encapsulating resin, the amount of the first encapsulating resin is adjusted such that the upper surface of the light-emitting element 110 is not covered with the first encapsulating resin.
After formation of the first encapsulating part 127A, a second encapsulating resin of, for example, a liquid silicone resin containing a phosphor is potted to cover the upper surface of the light-emitting element 110, and then cured, thereby forming a second encapsulating part 127B. When the second encapsulating resin is potted to a position near the upper end of the first projection 125, the second encapsulating resin is attached to the wires 116 in contact with the upper end of the first projection 125 and is raised, and thus extends to the upper end of the first projection 125. When the second encapsulating resin is further potted, the second encapsulating resin is lifted by the wires 116 vertically drawn from the upper surface of the light-emitting element 110. Thus, the upper surface of the second silicone resin is held by the wires 116, and is gradually raised from the outer rim toward the center of the region surrounded by the first projection 125. Above the light emission region of the light-emitting element 110, since no wires supporting the second encapsulating resin are present, an indentation is formed. By curing the second encapsulating resin in this state, the second encapsulating part 127B having its thickness gradually increase from the outer rim to the center and having an indentation 127a at the center thereof is formed.
The second encapsulating part 127B containing a phosphor is preferably relatively thick on the light-emitting element 110 in order to convert the wavelength of light efficiently. However, if the first projection 125 is excessively high, light travelling sideways is blocked. On the other hand, a configuration in which the wires 116 lift the encapsulating resin can ensure a sufficient thickness of the second encapsulating part 127B while reducing an increase in the height of the first projection 125. This configuration can also reduce an overflow of the second encapsulating resin across the first projection 125.
Since the wires 116 are connected to the p-side electrode and the n-side electrode located at both sides of the light-emitting element 110 with the center (i.e., the light emission region) thereof sandwiched therebetween, the indentation 127a is formed immediately above the light emission region. Accordingly, the indentation 127a is located immediately under the recess 141a provided in the light-control lens 114.
The wires 116 only need to be formed such that in potting the second encapsulating resin, the second encapsulating resin is made higher than the upper end of the first projection 125 by means of surface tension and lifting by the wires 116 to prevent the second encapsulating resin from overflowing across the first projection 125. Thus, although the wires 116 are in contact with the upper end of the first projection 125 in
Subsequently, using a mold having a cavity in the shape of the light-control lens 114, a light-control lens 114 is molded on a board 112 by transfer molding.
Then, the lead frame assembly 161 is diced into lead frames 121 with a dicer, thereby obtaining light emitting devices 32.
Before molding the light-control lens 114, a transparent liquid silicone resin, for example, may be potted onto a region surrounded by the second projection 126 to encapsulate the wires 116 and 118. The encapsulation of the wires 116 and 118 can reduce the possibility of disconnection of the wires 116 and 118 in forming the light-control lens 114.
Then, reflection of light by the first reflective surface 125A and the second reflective surface 126A will be described. The first projection 125 serving as the first reflector and the second projection 126 serving as the second reflector are formed in the shape of concentric circles about the light-emitting element 110. The height of the second projection 126 located outside the first projection 125 is larger than that of the first projection 125. Thus, as illustrated in
Then, the shape of the light-control lens 114 will be described. As illustrated in
The region C1 is a range having an angle θ1 of about 0°-3°, and corresponds to a portion near the bottom of the recess 141a. The region C1 serves as a reflective surface on which light incident from the direction of the light emission region of the light-emitting element 110 to the direction away from the optical axis L. In this region, the reflection angle increases as the distance from the optical axis L increases and the angle θ1 increases. Accordingly, light emitted immediately upward from the light-emitting element 110 is not directly emitted from the emission surface S of the light-control lens 114. Thus, it is possible to reduce a considerable rise of the emission intensity near the optical axis L.
In the indentation 127a of the second encapsulating part 127B containing the phosphor, the phosphor has a low efficiency of wavelength conversion. However, since the indentation 127a is located immediately under the recess 141a, light incident on the region C1 through the indentation 127a is reflected, and sufficiently mixed with the color of ambient light. Thus, advantageously, the difference in chromaticity caused by the indentation 127a can be made less visible from immediately above.
The region C2 is a range having an angle θ1 of about 3°-7°, and corresponds to a range from a portion near the bottom of the recess 141a to a portion near the lower end of the slope of the recess 141a. The region C2 is a refractive surface which has a high ratio θ2/θ1 and in which light incident from the direction of the light emission region is refracted to the direction away from the optical axis L. As the angle θ1 increases, the ratio θ2/θ1 increases and the refraction angle increases. Thus, in the region C2 that is a circumferential surface continuous to the outer periphery of the region C1, concentration of light to a portion near optical axis L can be avoided, and a decrease in emission intensity caused by total reflection of light in the region C1 can be compensated for.
The region C3 is a range having an angle θ1 of about 7°-24°, and corresponds to a range from a portion near the lower end of the slope of the recess 141a to a portion near the upper end of the recess 141a. The region C2 serves as a reflective surface on which light incident from the direction of the light emission region is totally reflected in the direction away from the optical axis L. In the same manner as in the region C1, as the angle θ1 increases, the reflection angle increases. Thus, in the region C3, light around the optical axis L is dispersed from the direction immediately above to the outward direction.
The region C4 is a range having an angle θ1 of about 24°-37°, and corresponds to a range from a portion near the upper end of the recess 141a to a portion near the middle of the horizontal surface 141b. The region C4 serves as a refractive surface which has a ratio θ2/θ1 greater than 1 (one) and in which light incident from the direction of the light emission region is refracted to the direction away from the optical axis L. However, the refraction angle is smaller than the angle θ2 (i.e., the ratio θ2/θ1 is about 2.5-1.5), and conversely to the region C2, as the angle θ1 increases, the refraction angle decreases. Thus, in the region C4, concentration of light to a portion near optical axis L can be avoided, and a decrease in emission intensity caused by total reflection of light on the region C3 can be compensated for.
The region C5 is a range having an angle θ1 of about 37°-43°, and corresponds to a portion near the middle of the horizontal surface 141b. The region C5 serves as a refractive surface in which light incident from the direction of the light emission region is refracted in the direction away from the optical axis L, and as the angle θ1 increases, the refraction angle slightly increases.
The region C6 is a range having an angle θ1 of about 43°-70°, and corresponds to a range extending from a portion near the middle of the horizontal surface 141b to the peripheral surface 141d and including the arc surface 141c. The region C6 serves as a refractive surface in which the refraction angle decreases as the angle θ1 increases. The ratio θ2/θ1 is 1 (one) near the boundary between the region C6 and the region C7.
The region C7 is a range having an angle θ1 of about 70°-82°, and corresponds to the flat portion 141f. The flat portion 141f is slightly sloped from the lower end to the upper end thereof to approach the optical axis L gradually. Accordingly, in the region C7, the ratio θ2/θ1 is less than 1 (one), and light incident from the direction of the light emission region is refracted toward the optical axis L. Since the flat portion 141f is located to oppose a longer side of the light-emitting element 110, light travelling sideways from the longer side of the light-emitting element 110 can be refracted toward the optical axis L, thereby increasing emission intensity immediately above the light-emitting element 110.
The region C8 is a range having an angle θ1 of about 82°-90°, and corresponds to the bottom portion 141e. In the region C8, the ratio θ2/θ1 is much less than 1 (one), and light incident from the direction of the light emission region is refracted toward the optical axis L. As the angle θ1 increases, the refraction angle increases.
As illustrated in
Since the light emitting device 32 of this embodiment includes the second projection 126 as well as the first projection 125, light emitted from the light-emitting element 110 does not directly reach the bottom portion 141e. However, part of light reflected on the emission surface S of the light-control lens 114, for example, reaches the bottom portion 141e, and thus, a region immediately above the light-emitting element 110 can be irradiated. This configuration is expected to contribute to uniformization of the emission intensity.
The light-control lens 114 includes the region C1 and the region C3 on which light travelling from the light-emitting element 110 toward the optical axis L is totally reflected to a direction away from the optical axis L. The first reflective surface 125A is located below the region C1 and the region C3, and light collected toward the optical axis L by the first reflective surface 125A is reflected on the region C1 and the region C3 in a direction away from the optical axis L. In this manner, a wide range can be irradiated.
The region C3 has a reflection angle that gradually increases as the distance from the optical axis L increases. Thus, as the distance from the optical axis L increases, the reflection angle of light reflected on the first reflective surface 125A and entering the region C3 increases, and the light is reflected in a direction away from the optical axis L. In this manner, the region C3 can disperse light to the surrounding while reducing light travelling immediately upward from light-emitting element 110, thereby enabling more uniform irradiation with light. In addition, since light emitted from the light-emitting element 110 and entering the region C3 is reflected to the direction away from the optical axis L, a wide range can be irradiated.
The light emitting device 32 of this embodiment includes the light-control lens 114 having a curved surface, the first reflector constituted by the first projection 125, and the second reflector constituted by the second projection 126. Thus, it is possible to obtain light distribution characteristics in which a larger amount of light is distributed to the periphery of the optical axis L than to the optical axis L itself, as illustrated in
Then, luminance characteristics of the light emitting device 32 will be described. Since the light-emitting element 110 has a substantially rectangular solid shape, the luminance is higher in its longer sides than in its shorter sides. On the other hand, the light-control lens 114 has the flat portions 141f opposing the longer sides of the light-emitting element 110. Since the flat portions 141f do not have convex curves, the flat portions 141f have a small lens effect. In this manner, even in the case where the light-emitting element 110 has a substantially rectangular solid shape, the emission intensity at the longer sides can be made equal to that at the shorter sides, thus enabling substantially uniform irradiation in all the directions.
As described above, the light emitting device 32 of this embodiment can substantially uniformly distribute light to a region around the light-control lens 114. Accordingly, in the surface light source part 30 as illustrated in
In this embodiment, two reflective surfaces concentrically surrounding the light-emitting element 110 are provided. Alternatively, three or more reflective surfaces may be provided. In this case, upper ends of the reflective surfaces are located higher with increasing distance from the light-emitting element. In the embodiment, the innermost reflective surface is located immediately under the recess 141a in the light-control lens 114. Alternatively, at least one of the reflective surfaces only needs to be located immediately under the recess 141a.
In this embodiment, the inner side surface of the first projection 125 and the wall surface of the first opening 122a are sloped at the same angle, and the outer side surface of the first projection 125 is sloped at an angle different from that of the wall surfaces of the second opening 122b and the fourth opening 122d. Alternatively, as illustrated in
In a light emitting device according to the present invention, light emitted from a light-emitting element is efficiently guided upward, thereby enhancing the emission efficiency, and is particularly useful as, for example, a light emitting device and/or a surface light source device including a reflector that reflects light emitted sideways from the light-emitting element.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-231243 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/005740 | 10/13/2011 | WO | 00 | 3/4/2013 |
