JP2004127934A - Planar light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light emitting device having high and uniform luminance. <P>SOLUTION: This planar light emitting device has light sources; and a light guide plate for making light of the light sources incident from a side surface to emit the light from the upper surface. The planar light emitting device is so structured that at least one of the side surfaces of the light guide plate has an uneven part; the incident surface of the light guide plate has a plurality of stepped surfaces continuing at predetermined steps from the upper surface to the bottom surface; the stepped surfaces on the upper surface side are formed so as to project in the direction of the light sources with respect to the continuing bottom surface side; and the light sources are so disposed on the respective stepped surfaces on the upper surface side and on the bottom surface side as to face the respective stepped surfaces. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a planar light emitting device used for a liquid crystal backlight, a panel meter, an indicator lamp, a surface light switch, and the like.

Conventionally, as a light source such as a liquid crystal backlight, a planar light emitting device that emits light from a semiconductor light emitting element, for example, a light emitting diode (hereinafter, referred to as an LED) in a planar manner has been used. FIG. 9 shows an example of the structure of the planar light emitting device. The planar light-emitting device 100 includes a light-transmitting light guide plate 101 and an LED 102 provided on one end surface of the light guide plate 101 and allowing light to enter from the end surface of the light guide plate. Most of the light from the LED 102 is guided into the light guide plate 101 from the incident surface 105 of the light guide plate 101. Further, the lost light is also reflected by the reflector 103 and guided to the incident surface 105 of the light guide plate 101. In addition, a reflection plate 104 is provided except for an emission surface 106 of the light guide plate 101 and an end surface where the LEDs are arranged to face each other, and incident light from the LEDs is reflected by the reflection plate 104 and emitted from the emission surface 106. Further, a prism sheet (not shown) separate from the light guide plate is disposed on the light-exiting surface in order to increase the ratio of light emitted in the direction of the light-exiting surface to improve the brightness of the backlight (for example, see Patent Document 1). 1) has also been proposed.
JP-A-2002-107515

However, in order to increase the light emitting area of the surface light emitting device or to perform surface light emission with higher luminance, there is a problem as described below when further increasing the luminance of the LED as a light source. That is, the light from the LED has a directional characteristic of emitting light radially at a certain directional angle. For this reason, the light emission intensity near the LED is strong, and the light emission intensity becomes weaker as the distance from the LED increases, which tends to cause uneven brightness. In particular, corners viewed between the LEDs and from the emission surface side tend to be dark. Furthermore, when a high-brightness LED whose light emission intensity has been improved to several thousand mcd is made to emit light fully, there is an advantage that the number of LED chips can be reduced and the size can be reduced. An intensity distribution results. On the other hand, a method is considered in which a reflection pattern is provided on the bottom surface of the light guide plate opposite to the emission surface, and incident light is scattered and reflected in the light guide plate to make luminance uniform. However, it is difficult to eliminate the intensity distribution of light emission in the vicinity of the LED using only this method.
In addition, when the prism sheet is used, it is difficult to reduce the thickness of the light emitting device, and there is a problem that the manufacturing process is complicated due to an increase in the number of components.
Therefore, an object of the present invention is to provide a planar light emitting device having high luminance and uniform luminance.

In order to solve the above problems, a planar light emitting device of the present invention is a planar light emitting device having a light source, and a light guide plate that causes light from the light source to enter from a side surface and emit from a top surface by reflection, and At least one side surface of the light guide plate has an uneven portion, and the incident surface of the light guide plate has a plurality of step surfaces continuous from the upper surface to the bottom surface of the light guide plate at a predetermined step. A light source is arranged so as to protrude in the direction of the light source with respect to a continuous bottom surface side surface, and to each of the top surface side surface surface and the bottom surface side surface surface so as to face each step surface. This is a planar light emitting device characterized by comprising: Here, it is preferable that the light sources are alternately arranged on the step surface on the top surface and the step surface on the bottom surface along the longitudinal direction of the incident surface. Thereby, transmission of light from the side surface is suppressed.

In addition, the planar light emitting device of the present invention can use, as the concavo-convex portion, a prism row composed of a number of protrusions having a continuous triangular cross section. Also, an uneven portion can be provided on the upper surface of the light guide plate.

In addition, in the planar light emitting device of the present invention, the light source is disposed so as to face the light incident surface of the light guide plate, and the light incident surface may be provided with an uneven portion.

In the planar light emitting device of the present invention, since the uneven portion is provided on at least one side surface of the light guide plate, light from the light source is reflected on the uneven portion, and transmission of light to the side surface can be prevented. This makes it possible to reduce the number of reflectors and improve the light extraction efficiency. Further, by providing the projections and depressions on the emission surface, the emission direction can be adjusted and the proportion of light emitted perpendicular to the emission surface can be increased, so that the emission luminance can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic plan view showing the structure of the planar light emitting device C according to the present embodiment, FIG. 2 is a side view, and FIG. 3 is a perspective view. The planar light emitting device C has two light source arrays arranged on two step surfaces provided on the side surfaces.
The planar light-emitting device C has a light-transmitting light guide plate 5 and two light source arrays 1 and 2. The incident surface 5c of the light guide plate 5 has a first step surface 51c and a second step surface 52c that are continuous from the upper surface 5a to the bottom surface 5b with a predetermined step, and the first step surface 51c is It is formed so as to protrude in the direction of the light source with respect to the second step surface 52c. The first light source array 1 is arranged to face the first step surface 51c, and the second light source array 2 is arranged to face the second step surface 52c. Here, the first light source row 1 and the second light source row 2 are respectively composed of a plurality of LEDs 1a and 2a arranged linearly in the longitudinal direction of the incident surface, and the LED 1a and the LED 2a are arranged in the longitudinal direction of the incident surface. Are alternately arranged on the first step surface 51c and the second step surface 52c.

The light guide plate 5 includes an emission surface 5a as an upper surface, a bottom surface 5b facing the emission surface 5a, an incidence surface 5c on which light from the LED is incident, a side surface 5d facing the incidence surface 5c, and an incidence surface. It has a pair of side surfaces 5e and 5f which are adjacent to and opposed to 5c. Further, an uneven portion composed of a prism array shown in FIG. 3 is formed on the entire surface of the light guide plate 5 except for the LED mounting surfaces 5g and 5g '.

In this embodiment, since two light sources are provided on the side surface and the brightness is high, an extremely strong light emission intensity distribution is generated in the vicinity of the LED constituting the light source. However, light that has entered the light guide plate from the two light sources is reflected inside the light guide plate, partly returns to the incident surface, is reflected by the incident surface, and exits from the exit surface. Therefore, the uneven brightness near the LED is eliminated, and the uniformity of the brightness can be improved. In particular, by arranging the LEDs 1a and the LEDs 2a alternately along the longitudinal direction of the incident surface, the intensity distribution of light emission in the vicinity of the LED is made more uniform, so that uneven brightness in the vicinity of the LED is more effectively eliminated. can do.

In addition, since the light source row composed of one or more LEDs is arranged on each of the two step surfaces provided on the side surfaces, many light sources can be arranged on the incident surface without increasing the size of the light guide plate, thereby saving space. A light emitting device can be provided.

Further, the light source of the first light source row has a longer optical path than the light source of the second light source row, so that the brightness is lower than the light source of the second light source row, but the directivity is weakened, and The color mixing between them becomes high. On the other hand, since the light sources of the second light source row have a short optical path, they are less likely to be reflected and scattered inside the light guide plate, resulting in high brightness. Therefore, according to the light emitting device of the present embodiment, it is possible to achieve both high luminance and color mixing.
Note that, in the present embodiment, the case where there are two step surfaces is shown. However, even when the number of step surfaces is three or more, the same effect as that of the present embodiment can be obtained.

According to the present embodiment, since the side surface can prevent the transmission of light to the side surface without using a reflector, the light extraction efficiency can be improved. Further, the prism array provided on the exit surface adjusts the exit direction so as to increase the proportion of light exiting perpendicular to the exit surface. Thus, the luminance of the light emitting device can be improved. In addition, when a high-brightness LED emits full light, an extremely strong emission intensity distribution is generated in the vicinity of the LED serving as a light source. By providing a prism array on the incident surface, transmission of light from the incident surface is prevented. However, since light can be introduced into a dark portion near the LED, the luminance can be made uniform.

Further, conventionally, for the reflection plate, polyethylene terephthalate, polycarbonate, and a sheet-like material molded by containing a white pigment or a scattering material in a resin such as polypropylene is used, according to the present embodiment, Since the number of reflectors can be reduced, the light emitting device can be manufactured at lower cost.

As a material constituting the light guide plate, a material excellent in light transmittance and molding, for example, a polycarbonate resin, an acrylic resin, an amorphous polyolefin resin, a polystyrene resin and the like can be mentioned.

In order to manufacture a light guide plate having a desired uneven portion, the light guide plate can be manufactured by, for example, an injection molding method using a mold having a desired uneven pattern. When a prism row is used for the uneven portion, the prism pitch is preferably 30 to 100 μm. If the prism pitch is smaller than 30 μm, the depth of the V-shaped groove between the prisms becomes shallow, the proportion of light emitted perpendicular to the exit surface decreases, and the luminance decreases. On the other hand, if it is larger than 100 μm, the ratio of the reflected light decreases, and the luminance decreases.
Further, the apex angle of the prisms of the first prism row 32 is preferably 80 to 120 degrees. This is because, by causing total reflection and increasing the reflected light and confining the light inside the light guide plate, it is possible to increase the proportion of light emitted perpendicularly to the exit surface.

Further, the light guide plate may contain a diffusing agent for more uniform light emission, or may contain a coloring agent to emit light of a desired emission color. A diffusing agent or a coloring pigment may be uniformly dispersed in the light guide plate, or may be inclinedly distributed. Examples of the material of the diffusing agent include an acrylic resin, a polycarbonate resin, an amorphous polyolefin resin, and a polymethylenepentene resin. Various pigments and dyes can be used as the colorant. Further, a fluorescent dye or a fluorescent pigment can also be used.

金属 Alternatively, a metal film having high reflectivity such as Al, Ag, and Cu can be formed on the bottom surface of the light guide plate by sputtering or vacuum evaporation. Thereby, the reflectance of the bottom surface can be increased, and the light extraction efficiency can be further improved.

に お い て In the present invention, any other light emitter such as a light bulb, a fluorescent lamp, a laser diode, etc. can be used as the light source. Various light emitting diodes that can be used as the light source of the present invention can be used as long as light can be efficiently introduced into the light guide plate. The light emitting diode may be an SMD (surface emitting type) light emitting diode or a shell type light emitting diode. Further, the LED chip itself, which is a light emitting element, may be used.

Further, as a material of the light emitting element, various semiconductors such as BN, SiC, ZnSe, GaN, InGaN, InAlGaN, AlGaN, BAlGaN, and BInAlGaN can be given. Similarly, these elements may contain Si, Zn, or the like as an impurity element to serve as a light emission center. As the semiconductor structure, a homo structure, a hetero structure, or a double hetero structure having a MIS junction, a PIN junction, a pn junction, or the like can be preferably exemplified. Various emission wavelengths can be selected depending on the material of the semiconductor layer and its mixed crystal ratio. The output can be further improved by using a single quantum well structure or a multiple quantum well structure in which the semiconductor layer is formed as a thin film in which a quantum effect occurs.

In addition, two or more light emitting elements can be used, and two or more light emitting elements can be used. When two or more types are used, various emission colors can be obtained by mixing the emission colors. White light can be emitted by mixing all the light emitting elements with RGB (red, green, blue) or BY (blue, yellow).

As the white light emitting capable emitting element in combination with a phosphor, a blue light emission can be a nitride-based semiconductor _{(In x Al y Ga 1-} x-y N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) The used light emitting element can be suitably used. In this case, it is preferable to use a YAG: Ce phosphor or a perylene derivative as the phosphor. In the case of a light-emitting element that emits ultraviolet light, an alkaline earth metal halogen apatite phosphor activated with Eu containing at least Mn and / or Cl can be used.

場合 When a nitride semiconductor is used, sapphire, spinel, SiC, Si, ZnO, GaAs, GaN, or the like can be suitably used for the semiconductor substrate. In order to form a nitride semiconductor with good crystallinity with high productivity, it is preferable to use a sapphire substrate. A nitride semiconductor can be formed on the sapphire substrate by using the HVPE method, the MOCVD method, or the like. On a sapphire substrate, a buffer layer made of non-single crystal such as GaN, AlN, and GaAlN is formed by low-temperature growth, and a nitride semiconductor having a pn junction is formed thereon.

As an example of a light emitting element that can efficiently emit light in an ultraviolet region having a pn junction using a nitride semiconductor, SiO ₂ is formed on a buffer layer in a stripe shape substantially perpendicular to the orientation flat surface of a sapphire substrate. GaN is grown on the stripe by ELOG (Epitaxial Lateral Over Growth) using HVPE. Subsequently, a first contact layer formed of n-type gallium nitride, a first cladding layer formed of n-type aluminum gallium nitride, a well layer of indium aluminum gallium nitride and aluminum gallium nitride are formed by MOCVD. , An active layer having a multiple quantum well structure in which a plurality of barrier layers are stacked, and a double hetero structure in which a second contact layer formed of p-type gallium nitride is sequentially stacked.

Nitride semiconductor shows n-type conductivity without doping impurities. When a desired n-type nitride semiconductor is formed, for example, to improve luminous efficiency, it is preferable to appropriately introduce Si, Ge, Se, Te, C, or the like as an n-type dopant. On the other hand, when forming a p-type nitride semiconductor, it is preferable to dope a p-type dopant such as Zn, Mg, Be, Ca, Sr, and Ba. Since it is difficult to make a nitride semiconductor p-type only by doping it with a p-type dopant, it is preferable to lower the resistance by introducing a p-type dopant by heating in a furnace or irradiating plasma. Each contact layer is exposed by etching from the p-type side up to the surface of the first contact layer. After the electrodes are formed on the respective contact layers, the semiconductor wafer is cut into chips to form a light emitting element made of a nitride semiconductor.

The planar light emitting device of the present invention can emit light from a light emitting element into various colors by a color conversion member, and emit light in a planar manner, in addition to emitting light from the light emitting element in a planar state. The color conversion member can take various forms, for example, a coating film containing a phosphor may be formed on the light incident surface of the light guide plate, and a sheet holding the phosphor may be formed on the light exit surface of the light guide plate. Can also be placed. A specific color conversion member is formed by applying a resin containing a phosphor to a sheet-like base film having a light transmittance of 70% or more with respect to light from the light emitting element using a roll coater or the like. be able to. As such a base film, a polycarbonate film or a polyester film having high translucency and heat resistance are preferably exemplified. As the base film, in order to further improve the uniformity of light emission, a film coated with refractive fine resin beads or translucent inorganic fine particles, and a film obtained by embossing the above film can be suitably used. Further, a more uniform white display can be obtained by containing a white pigment together with the phosphor.

The above-described phosphor can be used as the phosphor contained in the color conversion member. That is, in the case of the light emitting device using a blue light emitting capable nitride semiconductor _{(In x Al y Ga 1-} x-y N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), YAG is the phosphor: Ce It is preferable to use a phosphor or a perylene derivative. In the case of a light-emitting element that emits ultraviolet light, it is preferable to use an alkaline earth metal halogen apatite phosphor activated with Eu containing at least Mn and / or Cl.

In the above-described first embodiment, no irregularities were formed on the LED mounting surface surfaces 5g and 5g '. However, the LED mounting surface surfaces 5g and 5g' were the same as the other surfaces. An uneven portion may be formed on the surface. By forming the concave and convex portions on the mounting surfaces 5g and 5g 'of the LED as described above, it is possible to effectively eliminate the intensity distribution of light emission in the vicinity of the LED.

Also, in the embodiment, the prism rows having the shape shown in FIG. 3 are used, but the uneven portions used in the present invention are not limited to the prism rows having the shape shown in FIG. For example, the following modifications are possible.

(Modification 1)
FIG. 4 is a schematic diagram showing the shape of the uneven portion according to this modification, and shows an example in which the present invention is applied to the planar light emitting device of the first embodiment. The concavo-convex portion of the present modified example is a prism row, and includes a first prism row 32 formed at a predetermined prism pitch and one or more prisms formed between two adjacent prisms of the first prism row. And the second prism row 33 is formed such that the cross-sectional area of the prisms of the second prism row 33 is smaller than the cross-sectional area of the prisms of the first prism row 32.

By forming two types of prism rows each including a prism having a different cross-sectional area, it is possible to increase reflected light and increase the proportion of light emitted perpendicular to the exit surface.
FIG. 7 is a schematic enlarged view of the uneven portion according to the present modification. As described above, the prism pitch of the first prism row is preferably 30 to 100 μm, and the apex angle of the prisms of the first prism row 32 is preferably 80 to 120 degrees.
The prism pitch of the second prism row 33 is preferably 5 to 20 μm, and the width in the pitch direction is preferably 15 to 60 μm.
The vertex angle of the prism is preferably 80 to 120 degrees. This is because, by causing total reflection and increasing the reflected light and confining the light inside the light guide plate, it is possible to increase the proportion of light emitted perpendicularly to the exit surface.

(Modification 2)
FIG. 5 is a schematic diagram showing the shape of the uneven portion according to this modification, and shows an example in which the present invention is applied to the planar light emitting device of the first embodiment. The uneven portion of this modification is a prism row, and a first ridge 34 having a prism row composed of a large number of second ridges 34a having a continuous triangular cross section on the surface is continuous at a predetermined pitch. It is formed.
By forming a fine first ridge on the surface of the second ridge, reflected light is increased, and light is confined inside the light guide plate, thereby increasing the proportion of light emitted perpendicular to the emission surface. can do.

(Modification 3)
FIG. 6 is a schematic diagram showing the shape of the uneven portion according to this modification, and shows an example in which the present invention is applied to the planar light emitting device of the first embodiment. In the concavo-convex portion of the present modified example, a pyramid-shaped portion 35 is continuously arranged vertically and horizontally instead of a prism array having a triangular cross section.
As in the case of using the prism array, the light from the light source is reflected on the pyramid-shaped portion to increase the reflected light, and the proportion of the light emitted perpendicular to the emission surface can be increased.

Here, as shown in the schematic enlarged view of FIG. 8, the bottom surface of the pyramid-shaped portion 35 has a square shape, and the length of one side is preferably 10 to 100 μm. If the length of one side is smaller than 10 μm, the depth of the V-shaped groove between the pyramid-shaped portions becomes shallow, the proportion of light emitted perpendicular to the exit surface decreases, and the luminance decreases. On the other hand, if it is larger than 100 μm, the ratio of the reflected light decreases, and the luminance decreases. It is preferable that the angle at which the opposing inclined surfaces of the prism 35 intersect is 80 to 120 degrees. This is because reflected light can be increased to increase the proportion of light emitted perpendicular to the exit surface. Note that the pyramid-shaped portion 35 may be convex in the inner direction of the light guide plate 3 or convex in the outer direction of the light guide plate 3.

FIG. 2 is a schematic plan view showing the structure of the planar light emitting device according to Embodiment 1 of the present invention. FIG. 2 is a schematic side view showing the structure of the planar light emitting device according to Embodiment 1 of the present invention. FIG. 2 is a schematic view showing a structure of the planar light emitting device according to Embodiment 1 of the present invention, and is a perspective view including a partially enlarged view. It is a schematic diagram which shows the structure of the planar light-emitting device which concerns on the modification 1 of this invention, and is a perspective view including a partially enlarged view. It is a schematic diagram which shows the structure of the planar light-emitting device which concerns on the modification 2 of this invention, and is a perspective view including a partially enlarged view. It is a schematic diagram which shows the structure of the planar light-emitting device which concerns on the modification 3 of this invention, and is a perspective view including a partially enlarged view. It is a typical enlarged view showing the surface shape of the surface light emitting device concerning modification 1 of the present invention. It is a typical enlarged view showing the surface shape of the surface light emitting device concerning modification 3 of the present invention. It is a schematic cross section which shows the structure of the conventional planar light emitting device.

Explanation of reference numerals

1, 2 light source rows,
1a, 2a light emitting element,
5 light guide plate,
5a top surface (emission surface),
5b bottom,
5c side surface (incident surface),
5d, 5e, 5f side,
5g, 5g 'mounting surface,
32 first prism row,
33 second prism row,
34 First ridge,
34a second ridge,
35 pyramid-shaped part,
51c first step surface,
52c second step surface,
C Planar light emitting device.

Claims (5)

A planar light emitting device having a light source and a light guide plate that causes light from the light source to enter the side surface and emit from the upper surface by reflection,
At least one side surface of the light guide plate has an uneven portion,
The incident surface of the light guide plate has a plurality of step surfaces that are continuous with a predetermined step from the top surface to the bottom surface of the light guide plate, and the step surface on the top surface projects in the direction of the light source with respect to the continuous step surface on the bottom surface. A planar light emitting device comprising: a light source disposed on each of a top surface side and a bottom surface side so as to face each step surface. The planar light emitting device according to claim 1, wherein the light sources are alternately arranged on a step surface on the upper surface side and a step surface on the bottom surface side along the longitudinal direction of the incident surface. (3) The planar light emitting device according to (1) or (2), wherein the uneven portion is a prism row including a number of protrusions having a continuous triangular cross section. 4. The planar light emitting device according to claim 1, wherein the uneven portion is provided on an upper surface of the light guide plate. The planar light emitting device according to any one of claims 1 to 4, wherein the light source is disposed so as to face an incident surface of the light guide plate, and the uneven surface is provided on the incident surface.

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