JP2005347010A - Planar lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar lighting device with color changes of irradiating light of a light source side and a side opposite to the light source, as conventional light guide plate materials are used. <P>SOLUTION: The planar lighting device is so structured that area densities of dots 15a, 15b as silver regions filmed on a white-color film 14 of a reflecting plate 13 are gradually decreased from an end 13c arranged at a light-incident side of the light guide plate toward the other end 13d arranged at the final end face side as side end face opposing the light-incident face, so that a reflectance of a blue-color light (near wavelengths of 430 nm) is increased from one end 13c toward the other end 13d. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In recent years, liquid crystal display devices have been widely used as display devices for electronic devices such as personal computers and mobile phones. Since a liquid crystal is not a self-luminous display element unlike a cathode ray tube or the like, for example, in a transmissive liquid crystal display device, an illuminating means for irradiating light to the liquid crystal panel is indispensable. Even in the transmissive liquid crystal display device, auxiliary illumination means is provided to enable use in a dark place. A planar illumination 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, and thus is suitable as an illumination means for such a liquid crystal display device. Is used. In addition, with the recent increase in performance of white light emitting diodes (LEDs), the number of planar lighting devices using white LEDs as a light source has increased in order to further reduce the size and thickness of planar lighting devices and reduce power consumption. ing.

  Fig.5 (a) is an exploded perspective view which shows the principal part of such a planar illuminating device. In FIG. 5A, the planar illumination device 100 includes a light guide plate 101, a white LED 102 disposed on the side of the light incident surface 101 c that is one side end face of the light guide plate 101, and the lower surface 101 b side of the light guide plate 101. And a reflection plate 103 disposed on the surface. Further, on the lower surface 101b of the light guide plate 101, regular reflection means or diffuse reflection means (not shown) is provided. 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 reflecting plate 103 is usually a diffuse reflection or regular reflection member made of a white film, a silver deposited film, or the like.

  In the 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 toward the end surface 101d. In the process, a part of the light reflected by the regular reflection means or the diffuse reflection means provided on the lower surface 101b is emitted from the emission surface 101a to irradiate an object to be illuminated such as a liquid crystal panel. At this time, the reflecting plate 103 reflects the light leaking from the reflecting surface 101b and makes it incident on the light guide plate 101 again, thereby improving the light utilization efficiency.

  In general, the light guide plate material is required to have high transparency in order to increase the brightness of the planar lighting device. In this regard, although the above-described polycarbonate resin has relatively good transparency as a whole, 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. FIG. 5 (b) shows an example of the spectral light transmittance of the polycarbonate resin when the thickness of the test piece is about 3 mm. In this example, the transmittance on the long wavelength side (about 500 nm or more) is shown. While it is maintained at about 85%, it can be seen that the transmittance in the wavelength region on the short wavelength side (wavelength 400 to 450 nm) corresponding to blue light is reduced to about 60 to 70%. . Therefore, white light that has entered the light guide plate usually propagates at least a few tens of millimeters within the light guide plate. Therefore, a light guide plate made of polycarbonate resin absorbs the blue component of white light during the propagation process. Thus, the luminous intensity of the blue light in the light emitted from the emission surface gradually decreases from the light incident surface side toward the end surface side.

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 a 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. 6, the portion showing a sharp peak near the wavelength of 430 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 a conventional planar lighting device, when such a white LED is used as a light source, the influence of absorption of the blue component by the light guide plate appears remarkably, so that the emitted light near the end surface turns yellow. there were. Conventionally, for such problems, it has been proposed to improve the spectral light transmittance characteristics by mixing an acrylic resin or the like with a polycarbonate resin (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. .

  In order to achieve the above object, a planar illumination device according to the present invention includes a light guide plate, a light source disposed on a side end surface of the light guide plate, and a reflector disposed on a lower surface of the light guide plate. In the planar lighting device, the reflection plate has a spectral reflectance that is different between a side where the light source is disposed and a side opposite to the side where the light source is disposed.

  In particular, the spectral reflectance is characterized in that the reflectance in the vicinity of a wavelength of 430 nm is larger on the side facing the side where the light source is disposed than on the side where the light source is disposed.

  Furthermore, the light guide plate is made of polycarbonate, and the light source is made of a white LED.

  Further, the reflection plate is formed by forming silver on a white film as a base material. In particular, the silver is formed in a dot shape, and the area density of the dots is determined by the light source. It is comprised so that it may become so small that it leaves | separates from the side by which it is arrange | positioned.

  In another aspect, the reflector is configured by performing white printing on a silver reflective film as a base material, and in particular, the white printing is performed in a dot shape, and the area density of the dots is The light source is configured to be smaller as it approaches the side where the light source is disposed.

  According to the planar illumination device of the present invention, the spectral reflectance of the reflection plate is different between the light incident surface side where the light source is disposed and the end surface side facing it, and thus is absorbed by the light guide plate. By selectively increasing the reflectance with respect to the wavelength component, it is possible to correct the spectral light intensity of the light emitted from the light guide plate without changing the resin material forming the light guide plate. In particular, by increasing the reflectance of blue light (near 430 nm) on the terminal surface side rather than the light incident surface side, the influence of absorption of the blue component by the light guide plate is corrected, and the terminal surface of the light emitted from the light guide plate The yellowing at the side can be improved. The present invention has a remarkable effect particularly in a planar illumination device including a light guide plate made of polycarbonate and a light source made of white LED.

  In addition, according to the present invention, the reflection of blue light can be achieved by forming silver on the white film in the form of dots or applying white printing on the silver reflective film in the form of dots and changing the area density of the dots. It is possible to easily form a reflector having a larger rate on the end surface side than on the light incident surface side, and at that time, by smoothly changing the area density of dots, the reflectance of the blue component can be changed seamlessly. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing a main part of a planar illumination device 10 according to an embodiment of the present invention. The planar illumination device 10 includes a light guide plate 11, a plurality of (three in the present embodiment) point light sources 12 disposed on the side of a light incident surface 11 c that is one end face of the light guide plate 11, and a light guide. And a reflecting plate 13 disposed on the lower surface 11b of the optical plate 11. The lower surface 11b is provided with regular reflection means or diffuse reflection means (not shown). The light guide plate 11 is a plate-shaped light guide formed by molding a transparent resin material, and in this embodiment, is made of polycarbonate resin. Therefore, the light guide plate 11 has a spectral transmittance characteristic as shown in FIG. The point light source 12 is a white LED and has a spectrophotometer as shown in FIG.

  In the present embodiment, the reflecting plate 13 extends from one end 13c disposed on the light incident surface 11c side of the light guide plate 11 to the other end 13d disposed on the terminal surface 11d side that is the side end surface facing the light incident surface 11c. On the other hand, the reflectance of blue light (wavelength around 430 nm) is increased. Hereinafter, although the specific aspect is demonstrated, first, the spectral reflectance characteristic of the silver reflective film and white film which are normally used as a reflecting plate in the conventional planar apparatus is demonstrated.

  FIG. 2 is a graph showing spectral reflectance characteristics of the silver reflective film and the white film. Here, the silver reflective film is a reflective member formed by depositing silver on a PET film as a base material by vapor deposition, and the white film is a PET film added with a white pigment such as barium sulfate or titanium dioxide. It is a reflecting member formed into a shape. As shown in the figure, the spectral reflectances of both have a significant difference in the tendency in the wavelength region corresponding to blue light (in the range of approximately 400 to 500 nm), and the silver reflective film reflects in this wavelength region. On the other hand, in the case of a white film, the reflectance is equal to or higher than the reflectance on the long wavelength side. Therefore, the reflectance of blue light of the reflecting plate can be locally adjusted by mixing the silver region and the white region on the same reflecting plate at an appropriate area ratio and changing the ratio. The white film may be whitened by adding fine bubbles to a resin material such as PET, or may be printed with white ink mainly composed of the white pigment as described above. Since these all exhibit the same spectral reflectance characteristics, the white region of the reflector in this embodiment may have any of these aspects.

  FIG. 3A and FIG. 3B are plan views showing the first embodiment of the reflecting plate 13, respectively. 3 (a) and 3 (b), the reflecting plate 13 is composed of a white film 14 as a base material and silver regions formed into dots 15a and 15b on the white film 14 by vapor deposition or the like. Has been. In the present embodiment, the dots 15a and 15b, which are silver regions, are provided so that the area density gradually decreases from one end 13c on the light incident surface 11c side toward one end 13d on the termination surface 11d side, Such a variation in the area density is caused by the reflection plate 13 shown in FIG. 2A by reflecting the area shown in FIG. 2B by decreasing the area of each dot 15a from the one end 13c toward the other end 13d. The plate 13 is realized by decreasing the number density of the dots 15b from the one end 13c toward the other end 13d.

  As described above with reference to FIG. 2, since the reflectance for blue light is higher in the white region than in the silver region, the area density of the dots 15a and 15b, which are silver regions, is increased from one end 13c toward the other end 13d. By making it small, the reflectance of the blue light of the reflecting plate 13 increases from the one end 13c toward the other end 13d. At this time, the area density of the dots 15a and 15b is preferably set so as to form a smooth gradation without exhibiting a rapid change.

  In the planar lighting device 10 including such a reflector 13, the light emitted from the white LED 12 enters the light guide plate 11 from the light incident surface 11 c and then between the light exit surface 11 a and the lower surface 11 b. Propagating to the end surface 11d side while repeating the reflection, and in the process, a part of the light reflected by the regular reflection means or the diffuse reflection means provided on the lower surface 101b is emitted from the emission surface 101a and is applied to a liquid crystal panel or the like. Illuminate the illuminator. At that time, the reflecting plate 13 functions to reflect the light leaking from the reflecting surface 11b and enter the light guide plate 11 again. In the present embodiment, the reflecting plate 13 has the spectral reflection as described above. Since it has a rate characteristic, the intensity of the blue component of the reflected light with respect to the blue component in the leaked light increases as it moves away from the light incident surface 11c side, so that the absorption of the blue component accompanying propagation in the light guide plate 11 is corrected. Thus, yellowing of the emitted light on the end surface side 11d is improved.

  FIG. 4A and FIG. 4B are plan views showing a second embodiment of the reflecting plate 13, respectively. 4 (a) and 4 (b), the reflecting plate 13 includes a silver reflecting film 16 as a base material and dots 17a and 17b formed by printing the above-described white ink on the silver reflecting film 16. And a white region. In the present embodiment, the dots 17a and 17b, which are white regions, are provided so that the area density gradually decreases from one end 13d on the end surface 11d side toward one end 13c on the light incident surface 11c side, Such a variation in area density is caused in the reflection plate 13 shown in FIG. 4A by reducing the area of each dot 17a from the one end 13d toward the other end 13c, thereby reflecting the area shown in FIG. 4B. The plate 13 is realized by decreasing the number density of the dots 17b from the one end 13d toward the other end 13c.

  As described above, the reflecting plate 13 in the present embodiment reduces the reflectance of blue light from the one end 13c to the other end 13c by decreasing the area density of the dots 17a and 17b, which are white regions, from the one end 13d to the other end 13c. It is increased toward the end 13d, and has the same effect as the reflector 13 in the first embodiment described above. The area density of the dots 17a and 17b is preferably set so as to form a smooth gradation without exhibiting a rapid change.

  Through the above-described embodiments, the area density of dots provided on the reflection plate and the rate of change thereof are appropriately set in consideration of the size of the light guide plate used, spectral transmittance characteristics, and the like. Further, the shape, size, and arrangement pattern of each dot are not limited to the modes shown in FIGS. 3 and 4, and are arbitrarily set as long as the appropriate area density and the rate of change thereof are maintained. For example, both the dot size and the number density may be varied, or the dot arrangement pattern may be randomly distributed.

In one Embodiment of the planar illuminating device which concerns on this invention, it is a disassembled perspective view which shows the principal part. It is a graph which shows the spectral reflectance characteristic of a silver reflective film and a white film. (A) is a top view which shows the one aspect | mode in 1st Embodiment of the reflecting plate which concerns on this invention, (b) is another in 1st Embodiment of the reflecting plate which concerns on this invention. It is a top view which shows an aspect. (A) is a top view which shows the one aspect | mode in 2nd Embodiment of the reflecting plate which concerns on this invention, (b) is another in 2nd Embodiment of the reflecting plate which concerns on this invention. It is a top view which shows an aspect. (A) is a disassembled perspective view which shows the principal part of the conventional planar illuminating device, (b) is a graph which shows the spectral transmittance characteristic of polycarbonate resin. It is a graph which shows the typical spectrophotometry of white LED.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Planar illumination apparatus 11 Light guide plate 12 Light source (white LED)
13 Reflector 14 White film 15a, 15b Silver dot 16 Silver reflection film 17a, 17b White print dot

Claims (8)

In a planar lighting device comprising a light guide plate, a light source disposed on a side end surface of the light guide plate, and a reflector disposed on a lower surface of the light guide plate,
The planar illumination device according to claim 1, wherein the reflector has a spectral reflectance that is different between a side where the light source is disposed and a side opposite to the side where the light source is disposed.   2. The spectral reflectance according to claim 1, wherein the reflectance in the vicinity of a wavelength of 430 nm is larger on a side facing the side where the light source is disposed than on a side where the light source is disposed. The surface illumination device described.   The planar lighting device according to claim 1, wherein the light guide plate is made of polycarbonate.   The planar illumination device according to claim 1, wherein the light source is a white LED.   The planar lighting device according to any one of claims 1 to 4, wherein the reflecting plate is configured by forming silver on a white film as a base material.   The planar illumination according to claim 5, wherein the silver is formed in a dot shape, and the area density of the dots is configured to decrease as the distance from the side where the light source is disposed. apparatus.   The planar lighting device according to any one of claims 1 to 4, wherein the reflecting plate is configured by performing white printing on a silver reflecting film as a base material. The planar illumination according to claim 7, wherein the white printing is performed in a dot shape, and the area density of the dots is configured to become smaller as it approaches a side where the light source is disposed. apparatus.

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