JP2012094283A - Planar lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve on color changes of irradiated light at a light source side and an opposite side of a planar lighting system.SOLUTION: Intensity of blue-color light in the irradiated light from a main face 12a is gradually lowered from an incident side toward a terminal end side, as a blue-color component of white-color light is absorbed in the process of propagation inside a light guide plate 12. Such lowering is compensated through improvement of utilization efficiency of blue-color light with a blue-color light reflecting means arranged at least at an end face 12d of the light guide plate 12 by reflecting the blue-color light leaked from an end face side of the light guide plate 12 making it re-incident into the light guide plate 12, and further, by deflecting it with a dot pattern formed at the main face 12a to be irradiated from the main face 12a of the light guide plate. The blue-color light reflecting means may have a housing frame 20 itself structured of a blue-color reflecting material, or may have a part 20a opposed to the terminal end face 12d coated with a blue-color light reflecting material.

Description

The present invention relates to a planar illumination device used as illumination means such as a liquid crystal display device.

Nowadays, liquid crystal display devices are generally used as display devices for electronic devices such as personal computers and mobile phones. Since liquid crystal is not a self-luminous display element, for example, in a transmissive liquid crystal display device, illumination means for irradiating light to the liquid crystal panel is essential, and a transflective liquid crystal display device using external light However, auxiliary lighting means are provided to enable use in the dark. As an illuminating means of such a liquid crystal display device, a planar illuminating device having a light guide plate and a light source disposed on the side of the light guide plate as main components has an advantage that it can be easily reduced in thickness. Therefore, it is widely used in combination with a liquid crystal display device. In addition, with the recent improvement in performance of white light emitting diodes (LEDs), a planar lighting device using a white LED as a light source is generally used in order to further reduce the size and thickness of the planar lighting device and reduce power consumption. It has become.

FIG. 3 is an exploded perspective view showing a main part of such a planar illumination device. In FIG. 3, the planar illumination device 100 includes a light guide plate 101, a white LED 102 disposed on a side of a light incident surface 101 c that is one end face of the light guide plate 101, and a light emission surface (mainly) of the light guide plate 101. A light reflecting sheet 103 disposed on the lower surface (the other main surface) 101b facing the surface 101a. The light guide plate 101 is a plate-like light guide made of a transparent resin material such as polycarbonate resin, and the polycarbonate resin is excellent in heat resistance and impact resistance, and thus is particularly used in portable electronic devices and the like. It is suitable as a light guide plate material for a state lighting device. The light reflecting sheet 103 is usually a diffuse reflection or regular reflection member made of a white film, a silver deposited film, or the like.

If necessary, the main surfaces 101a and 101b of the light guide plate 101 are provided with, for example, a plurality of dome-shaped dots having a substantially circular shape, a substantially dotted shape, a substantially rectangular shape, or the like in plan view. In addition, the plurality of dots are usually provided so that the area density increases according to the distance from the light incident surface 101c in order to improve the luminance distribution of the illumination light emitted from the light emission surface 101a.

In such a planar illumination device 100, the light emitted from the white LED 102 enters the light guide plate 101 from the light incident surface 101c, and then repeats reflection between the light emission surface 101a and the lower surface 101b side of the end surface 101d. In the process, a part of the reflected light is reflected from the light reflection sheet 103 which is a regular reflection means or a diffuse reflection means provided on the lower surface 101b and is emitted from the emission surface 101a. Irradiate the object to be illuminated.

Incidentally, the material of the light guide plate 101 is generally required to have high transparency in order to increase the luminance of the planar lighting device. In this regard, the polycarbonate resin described above has relatively good transparency as a whole, but its spectral light transmittance rapidly decreases on the short wavelength side, and this decrease in transmittance is due to the plate thickness through which the light passes. It is known that it extends to the wavelength region of visible light with the increase of. Specifically, the transmittance on the long wavelength side (about 500 nm or more) is maintained at about 89.5%, whereas in the wavelength region on the short wavelength side (wavelength 400 to 450 nm) corresponding to blue light. The transmittance is reduced to about 88 to 89%. Therefore, since the white light that has entered the light guide plate propagates through the inside thereof at a distance of at least about several tens of millimeters, in the light guide plate 101 made of polycarbonate resin, the blue component of white light is generated during the propagation process. The blue light beam in the light emitted from the exit surface 101a is gradually reduced from the light incident surface 101c side toward the end surface 101d side after being absorbed.

On the other hand, at present, the mainstream of white light emission in an LED is a method of mixing blue light from a blue light emitting element and yellow light from a phosphor or the like that absorbs the blue light and emits complementary yellow light. (See, for example, Patent Document 1) A typical spectrophotometer of a white LED according to this method is as shown in FIG. In FIG. 4, the portion showing a sharp peak near the wavelength of 450 nm corresponds to blue light emitted directly from the light emitting element, and the portion showing a gentle peak around the wavelength of 580 nm corresponds to yellow light emitted from the phosphor or the like. . In the conventional planar illumination device, when such a white LED is combined with the light guide plate 101 made of polycarbonate resin to constitute the planar illumination device 100, the influence of absorption of the blue component by the light guide plate 101 appears remarkably. There is a problem that the emitted light in the vicinity of the end face 101d changes to yellow. Conventionally, it has been proposed to improve the spectral light transmittance characteristics by mixing an acrylic resin or the like with a polycarbonate resin to solve such a problem (see, for example, Patent Document 2).

JP 2003-179259 A Japanese Patent Laid-Open No. 2002-60609

However, the resin composition described in Patent Document 2 is more expensive than the conventional polycarbonate resin, and its spectral light transmittance characteristics are the transmittance of the blue component and a longer wavelength than that. The balance with the transmittance on the side is not necessarily sufficient.
In view of the above problems, an object of the present invention is to provide a planar illumination device that improves color change of emitted light between a light source side and a side facing the light source while using a conventional light guide plate material. .

(Aspect of the Invention)
The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

(1) A main surface including a light guide plate and a white light source disposed on one end face of the light guide plate, and light emitted from the white light source is incident on the inside of the light guide plate from the one end face A planar illumination device that propagates through the light guide plate while repeating reflection between the main surface and the other main surface opposite to the main surface, and emits from the main surface in the process. A planar illumination device in which a blue light reflecting means is disposed on an end surface facing one end surface.

The planar illumination device described in this section reflects light between the main surface and the other main surface after the light emitted from the white light source enters the light guide plate from one end surface of the light guide plate. Propagating to the end face opposite to the one end face while repeating, part of the white light is emitted from the main surface in the process, and illuminates an object to be illuminated such as a liquid crystal panel. At this time, the blue component of the white light is absorbed in the process of propagation in the light guide plate, and the blue light flux in the light emitted from the main surface is an end surface (termination surface) facing the one end surface that is the light incident surface. It gradually decreases toward the side. Such a decrease in the luminous flux of the blue light is reflected by the blue light reflecting means disposed on the end surface facing at least one side end surface of the light guide plate, and the blue light leaking from the end surface side of the light guide plate is reflected again to enter the light guide plate. It is supplemented by improving the utilization efficiency of blue light.

(2) The planar illumination device according to (1), wherein a dot pattern is formed on at least one main surface of the light guide plate.
In the planar illumination device described in this section, the blue light leaking from the end face side of the light guide plate is reflected by the blue light reflecting means, and the light incident on the light guide plate again is incident on at least one main surface of the light guide plate. The light is deflected by the formed dot pattern and emitted from the main surface of the light guide plate. Therefore, the blue component of the white light absorbed in the process of propagation in the light guide plate is complemented by the synergistic effect of the re-incidence of the blue light to the light guide plate by the blue light reflecting means and the deflection action of the re-incident light by the dot pattern. Then, the color imbalance of the illumination light on the end surface (termination surface) side facing the light incident surface side is eliminated.

(3) The planar illumination device according to (2), wherein the area density of the dot pattern increases in accordance with the distance from the one side end surface.
In the planar illumination device described in this section, the area density of the dot pattern formed on at least one main surface of the light guide plate increases in accordance with the distance from the one side end surface, so that the re-incident light by the dot pattern Is increased in accordance with the distance from the one end face. Then, the blue component of the white light absorbed in the propagation process in the light guide plate increases according to the re-incidence of the blue light to the light guide plate by the blue light reflecting means and the distance from the one side end face by the dot pattern. It complements in a well-balanced manner by the synergistic effect of the deflection action of re-incident light, and more effectively eliminates the color imbalance of illumination light on the end face (termination face) side facing the light incident face side.

(4) In the above items (1) to (3), the blue light reflecting means is a planar illumination device configured by a housing frame arranged so as to surround a side end surface of the light guide plate (claim 3). .
The planar illumination device described in this section reflects blue light leaking from the side end surface of the light guide plate by a housing frame that is disposed so as to surround the side end surface of the light guide plate, which constitutes the blue light reflecting means. By making the light incident again on the light guide plate and improving the utilization efficiency of the blue light, the decrease in the luminous flux of the blue light is compensated. In this case, at least a portion of the housing frame itself facing the end surface facing the one end surface of the light guide plate is made of a blue light reflecting material.

(5) In the above items (1) to (3), the blue light reflecting means is a planar shape disposed between the light guide plate and a housing frame disposed so as to surround a side end surface of the light guide plate. Lighting device (Claim 3).
In the planar illumination device described in this section, the blue light reflecting means disposed between the housing frame and the light guide plate reflects the blue light leaking from the side end surface of the light guide plate and makes it incident on the light guide plate again. This improves the utilization efficiency of blue light.
In this case, as the blue light reflecting means, for example, a plate or film made of a blue light reflecting material, or a plate or film coated with a blue light reflecting material is disposed between the housing frame and the light guide plate. Moreover, these plates and films are affixed to the end surface facing one side end surface of the light guide plate, or a portion facing the end surface of the housing frame. Further, a blue light reflecting material is applied to an end face facing one end face of the light guide plate or a portion facing the end face of the housing frame.

(6) In the above items (1) to (4), the white light source is a white LED, and the blue light reflecting means is a planar illumination device having a large spectral reflectance in the vicinity of a wavelength of 450 nm (claim 4).

The planar illumination device described in this section reflects light between the main surface and the other main surface after the light emitted from the white LED enters the light guide plate from one end surface of the light guide plate. Propagating to the end face opposite to the one end face while repeating, part of the white light is emitted from the main surface in the process, and illuminates an object to be illuminated such as a liquid crystal panel. At this time, the blue component of the white light is absorbed in the process of propagation in the light guide plate, and the blue light flux in the light emitted from the main surface gradually decreases from the light incident surface side toward the terminal surface side. Such a decrease in the luminous flux of the blue light is reflected by the blue light reflecting means disposed on the end surface facing at least one side end surface of the light guide plate, and the blue light leaking from the end surface side of the light guide plate is reflected again to enter the light guide plate. Therefore, it is supplemented by improving the utilization efficiency of blue light.
In particular, a typical spectrophotometer of a white LED has a portion having a sharp peak near a wavelength of 450 nm, which corresponds to blue light emitted directly from the light emitting element, and has a large spectral reflectance near a wavelength of 450 nm. The use efficiency of blue light is optimized.

(7) In the above items (1) to (6), the light guide plate is a planar illumination device made of polycarbonate resin (claim 5).
In the planar illumination device described in this section, the spectral light transmittance of the polycarbonate resin constituting the light guide plate is significantly reduced, particularly in the wavelength region on the short wavelength side corresponding to blue light, and propagation in the light guide plate is reduced. In the process, the blue component of the white light is absorbed, and the luminous flux of the blue light in the outgoing light from the main surface gradually decreases from the light incident surface side toward the terminal surface side. Such a decrease in the luminous flux of the blue light is reflected by the blue light reflecting means disposed on the end surface facing at least one side end surface of the light guide plate, and the blue light leaking from the end surface side of the light guide plate is reflected again to enter the light guide plate. It is supplemented by improving the utilization efficiency of blue light.

According to the planar illumination device according to the present invention, it is possible to improve the color change of the emitted light between the light source side and the side facing the light source while using the conventional light guide plate material.

(A) is a disassembled perspective view which shows the principal part of the planar illuminating device which concerns on embodiment of this invention, (b) is a graph which shows the spectral reflectance characteristic of the blue light reflection means of (a). And (c) is a plan view showing another embodiment of the light guide plate of (a). (A) It is a perspective view of the planar illuminating device which concerns on embodiment of this invention, (b) is a graph which illustrates the improvement effect of the chromaticity of the planar illuminating device shown by (a). It is a disassembled perspective view which shows the principal part of the conventional planar illuminating device. It is a graph which shows the typical spectrophotometry of white LED.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig.1 (a) is an exploded perspective view which shows the principal part of the planar illuminating device 10 in one Embodiment of this invention. The planar illumination device 10 includes a light guide plate 12, a plurality (three in this embodiment) of white light sources 14 disposed on the side of a light incident surface 12 c that is one end face of the light guide plate 12, and a light guide plate. And a light reflection sheet 16 as a regular reflection means or a diffuse reflection means, which is disposed on a lower surface (the other main surface) 12b facing the 12 emission surfaces (main surfaces) 12a. The light guide plate 12 is a plate-like light guide formed by molding a transparent resin material. In the present embodiment, the light guide plate 12 is made of polycarbonate resin. Therefore, the light guide plate 12 has the spectral transmittance characteristics as described in the related art.

Further, as in the conventional case, a plurality of dots are provided on at least one main surface 12a, 12b of the light guide plate 12. Since the dots are fine as will be described later, the illustration in FIG. 1 is omitted. As a method for forming the dots, for example, a method of integrally molding the surface of the light guide plate 12 with polycarbonate resin, a surface of the light guide plate 12 Include a method of forming a mat, a method of performing a specific wedge-shaped process, and a method of screen printing or vapor deposition of a predetermined ink or the like. Examples of the ink when formed by screen printing include volatile curable or ultraviolet curable ink containing fine particles for irregularly reflecting light.

Further, the area density of the dot pattern formed on the main surface (12a or 12b) of the light guide plate 12 is configured to increase as a whole in accordance with the distance from the one side end surface 12c, as in the prior art. . As a method of forming the dot pattern so as to increase the area density, for example, the dot pitch (center distance) is constant, and the dot area is increased according to the distance from the one side end face 12c. For example, the dot area may be constant and the dot pitch may be shortened according to the distance from the one side end face 12c. In the case of forming the dots, the dot area, for example, a 0.005~0.13mm ^2. The dot pitch is, for example, 0.08 to 0.3 mm. As an example, the dot area per unit area, that is, the dot occupation density (area density) is increased from 5% to 50%. Further, the dots may be arranged in parallel in the vertical direction and the horizontal direction of the light guide plate 12 or may be arranged so as to be partially offset.

Further, the white light source 14 encapsulates a blue light emitting LED chip with a translucent resin in which hard silicone resin is mixed with yttrium, aluminum, garnet (YAG) fine particles activated with cerium, which is a yellow light emitting phosphor. It is a white LED having a stopped structure and has a spectrophotometer as shown in FIG. The light guide plate 12, the white light source 14, and the light reflection sheet 16 correspond to the light guide plate 101, the white LED 102, and the light reflection sheet 103 of the conventional technology (see FIG. 3), respectively.
Furthermore, an optical sheet 18 such as a light diffusing plate is appropriately disposed on the emission surface 12 a of the light guide plate 12. The light guide plate 12, the white light source 14, the light reflection sheet 16, and the optical sheet 18 are accurately positioned by the housing frame 20 that is disposed so as to surround the side end surface of the light guide plate 12.

The housing frame 20 itself is made of a blue light reflecting material so that the blue light reflectance is increased. Note that the blue light reflecting material used here has a spectral reflectance characteristic as shown in FIG. 1B, and a material having a high reflectance at least in the vicinity of a wavelength of 450 nm is suitable.

Alternatively, blue light reflecting means different from the housing frame 20 may be disposed at least on the end surface (end surface) 12d facing the one side end surface 12c between the housing frame 20 and the light guide plate 12. The blue light reflecting means in this case is, for example, a plate or film made of a blue light reflecting material, or a plate or film coated with a blue light reflecting material, disposed between the housing frame 20 and the light guide plate 12. is there. Further, these plates and films may be attached to the end surface 12d of the light guide plate 12, or may be attached to the portion 20a of the housing frame 20 facing the end surface 12d. Furthermore, a blue light reflecting material may be applied to the end face 12d of the light guide plate 12 or the portion 20a of the housing frame 20 facing the end face 12d. Even in these cases, the blue light reflecting material used for each has spectral reflectance characteristics as shown in FIG. 1B, and has a high reflectance at least in the vicinity of a wavelength of 450 nm. Things are suitable.

  Further, as shown in FIG. 1 (c), a chamfered portion is provided at the corner of the light guide plate 12 having a rectangular shape as a whole, and the white light source 14 is disposed with the chamfered portion as the light incident surface 12c. It is also good. In this case, the two end surfaces facing the light incident surface 12c serve as the end surface 12d, and when blue light reflecting means made of a plate, film, or the like different from the housing frame 20 is used, at least these two end surfaces have blue color. A light reflecting means will be arranged. That is, regardless of the form of the light incident surface 12c of the light guide plate 12, it is sufficient that the blue light reflecting means is disposed at least on the end surface facing the light incident surface 12c.

Now, according to the embodiment of the present invention configured as described above, the following operational effects can be obtained.
In the planar illumination device 10 described in this section, the light emitted from the white LED that is the white light source 14 enters the light guide plate 12 from the one end surface 12c of the light guide plate 12, and then the main surface 12a and the other. While being repeatedly reflected from the main surface 12b, the light propagates to the end surface 12d facing the one end surface 12c, and in the process, part of the white light is emitted from the main surface 12a, and an object to be illuminated such as a liquid crystal panel Irradiate. At this time, the blue component of the white light is absorbed in the process of propagation in the light guide plate 12, and the blue light flux in the light emitted from the main surface 12a gradually decreases from the light incident surface side toward the terminal surface side. . Such a decrease in the luminous flux of blue light is guided again by reflecting the blue light leaking from the end face side of the light guide plate 12 by the blue light reflecting means disposed on the end face 12d facing the at least one side end face 12c of the light guide plate 12. It compensates by making it incident on the light plate 12 and improving the utilization efficiency of blue light.

Further, a dot pattern is formed on at least one main surface (12a or 12b) of the light guide plate 12 in order to efficiently emit light from the main surface (emission surface) 12a. For this reason, the blue light reflecting means reflects the blue light leaking from the end face side of the light guide plate 12 and is incident on the light guide plate 12 again. The light is deflected by the dot pattern and emitted from the main surface 12 of the light guide plate. The Rukoto.
Moreover, in the present embodiment, the dot pattern is formed so that the area density as a whole increases with the distance from the one side end face 12c in order to improve the luminance distribution of the light emitted from the emission face 12a. Yes. For this reason, the deflecting action of the re-incident light by the dot pattern can be increased according to the distance from the one side end surface 12c (in other words, the dot area density increases toward the end surface 12d side, and the end surface 12d side The blue light re-entered from the light guide plate 12 to the light guide plate 12 is emitted from the emission surface 12a as much as the terminal surface 12d side). As a result, the blue component of the white light absorbed in the process of propagation in the light guide plate 12 is re-entered into the light guide plate 12 by the blue light reflecting means and the distance from the one end face by the dot pattern. Thus, the increase in the re-incident light deflection action is complemented in a well-balanced manner, and the color imbalance of the illumination light on the end face 12d side is more effectively eliminated.

  Further, the blue light reflecting means is constituted by the housing frame 20 arranged so as to surround the side end face of the light guide plate 12, so that the blue light leaking from the side end face of the light guide plate 12 is reflected and again the light guide plate. By making the light incident on the light and improving the utilization efficiency of the blue light, it is possible to compensate for the decrease in the luminous flux of the blue light. In this case, at least a portion of the housing frame 20 itself facing the end surface 12d facing the one end surface 12c of the light guide plate 12 is made of a blue light reflecting material.

Further, as blue light reflecting means different from the housing frame 20, for example, a plate or film made of a blue light reflecting material, a plate or film coated with a blue light reflecting material, and the like between the housing frame 20 and the light guide plate 12. Similar effects can be obtained by arranging them in between. These plates and films are attached to the end face 12d of the light guide plate 12 or attached to the portion 20a of the housing frame 20 facing the end face 12d. Furthermore, a blue light reflecting material may be applied to the end face 12d of the light guide plate 12 or the portion 20a of the housing frame 20 facing the end face 12d.

In addition, as shown in FIG. 4, the typical spectrophotometer of the white LED corresponds to blue light emitted directly from the light emitting element, where the sharp peak in the vicinity of the wavelength of 450 nm corresponds to the wavelength. The use efficiency of blue light can be optimized by using a large blue light reflecting means in the vicinity of 450 nm.

Now, in FIG. 2, the chromaticity x, y of the planar illumination device according to the embodiment of the present invention is compared with the chromaticity of the planar illumination device according to the prior art.
In this example, the distance from the light incident surface 12c (FIG. 1) of the light guide plate 12 is set to Xmm, and measurement points P1 to P5 are measured using a color luminance meter as P1 to P5 in order from measurement points close to the light incident surface 12c. The chromaticity of was measured. Then, when the chromaticity difference between the measurement points is calculated by applying the equation Δxy = √ ((x1−x2) ² + (y1−y2) ² )), the measurement point (P2, P5) having the largest chromaticity difference is calculated. ) Value was improved from Δxy = 0.011 to Δxy = 0.005. Therefore, it has been clarified that the effect of absorption of the blue component by the light guide plate 12 is corrected, and an improvement effect can be obtained with respect to the yellowing of the outgoing light from the light guide plate 12 on the terminal surface 12d side.

DESCRIPTION OF SYMBOLS 10 Planar illuminating device, 12 Light guide plate, 12a: Output surface, 12b: Lower surface, 12c: Light entrance surface, 12d: Termination surface, 14: White light source (white LED), 20: Housing frame, 20a: Termination of light guide plate The part facing the surface

Claims (5)

A light guide plate and a white light source disposed on one side end surface of the light guide plate, and light emitted from the white light source is incident on the inside of the light guide plate from the one side end surface; A planar illumination device that propagates in the light guide plate while repeating reflection between the other main surface facing the surface and emits from the main surface in the process,
Blue light reflecting means is disposed on at least an end face of the light guide plate facing the one end face,
A planar illumination device, wherein a dot pattern is formed on at least one main surface of the light guide plate. The planar illumination device according to claim 1, wherein an area density of the dot pattern increases in accordance with a distance from the one end face. The blue light reflecting means is constituted by a housing frame disposed so as to surround a side end surface of the light guide plate, or is disposed between the housing frame and the light guide plate. 3. A planar illumination device according to 1 or 2. The planar illumination device according to any one of claims 1 to 3, wherein the white light source is a white LED, and the blue light reflecting means has a large spectral reflectance around a wavelength of 430 nm. The planar lighting device according to claim 1, wherein the light guide plate is made of polycarbonate resin.

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