Patent Application
20120140448
The present application claims priority from Japanese application JP2010-269876 filed on Dec. 3, 2010, the content of which is hereby incorporated by reference into this application.
The present invention relates to a backlight device which irradiates a liquid crystal panel with light and an image display using the same and more particularly to a backlight device which converts light from light source such as, for example, light emitting diodes (LED's) into surface light to irradiate the liquid crystal panel therewith and an image display using the same.
A backlight device for an image display using a liquid crystal panel as a display device uses light emitting diodes as a light source thereof in order to conform to energy saving and environmental regulation. Light emitting diodes are substantially point-like light sources and accordingly light from light emitting diodes is converted into surface light by means of plate-like light guide plate made of transparent resin, for example, to irradiate liquid crystal panel side with surface light, so that depth (thickness) of the backlight device can be made thinner and wide area can be irradiated.
JP-A-2006-236701, for example, is known as a prior art of such a backlight device using light guide plate. JP-A-2006-236701 discloses that plural depressions formed in bottom plane of light guide plate in longitudinal direction corresponding to horizontal direction are provided in vertical direction and plural side-emission type light emitting diodes are disposed in the respective depressions, so that light from light emitting diodes is reflected in light guide plate to irradiate the liquid crystal panel side.
In JP-A-2006-236701, light having the strongest intensity out of light from light emitting diodes mounted in depressions, that is, light near optical axis of light emission plane of light emitting diodes travels straight within light guide plate and reaches package on the back (surface opposite to light emission plane) of light emitting diodes mounted in depressions. This light having strong intensity is mostly absorbed in package on the back of light emitting diodes to be loss of light. Accordingly, unevenness in brightness occurs in the vicinity of depressions and the picture quality of displayed image is deteriorated. Further, temperature of light emitting diodes rises to thereby reduce the luminous efficiency of light emitting diodes.
It is an object of the present invention to provide technique suitable for reduction of unevenness in brightness in backlight device in which liquid crystal panel is irradiated with light from light sources such as light emitting diodes by means of light guide plate.
According to the present invention, a backlight device comprises light emitting diodes and a plate-like light guide plate which guides light from the light emitting diodes to a liquid crystal panel. Depressions are disposed on the back of the light guide plate and the light emitting diodes are disposed in the depressions. The light emitting diodes disposed in the depressions are arranged so that light emission direction thereof is parallel with light emission plane of the light guide plane. Optical patterns are formed on first side of the depressions which light from the light emitting diodes enters and on second side opposite to the first side.
The optical patterns may be surface subjected to roughening processing, for example, or may be formed into minute prism array or lens array.
Further, diffuse reflection members may be disposed in parts corresponding to the depressions on the side of light emission plane of the light guide plate.
According to the present invention, unevenness in brightness or increased temperature of light emitting diodes can be suppressed and image with high picture quality can be provided.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
A backlight device (or illumination device) and an image display using the backlight device according to an embodiment of the present invention are now described in detail with reference to the accompanying drawings. Elements having the same function and structure are designated by like reference numerals throughout the drawings and duplicate description is omitted.
Referring first to
In
The liquid crystal panel 1 controls transmissivity of liquid crystal pixels in accordance with inputted image signal to modulate light from backlight device 3 for each of liquid crystal pixels. Thus, image is formed in liquid crystal panel 1 in accordance with inputted image signal.
Referring now to
Referring now to
A plurality of depressions 6 (hereinafter also referred to as “grooves”) which are formed to extend in horizontal direction of the image display, for example, are disposed on the back of light guide plate 4, that is, on the surface opposite to chassis 12 of light guide plate 4. Light guide plate 4 has substantially fixed thickness except the grooves 6. Light emitting diodes 7 mounted on light source substrates 8 are disposed in grooves 6. Light emitting diodes 7 disposed in grooves 6 emit light in the same direction, here in right direction of the drawing. Light emitted from light emitting diodes 7 disposed in grooves 6 enters the side opposite to light emission plane of light emitting diodes 7 (hereinafter this side is referred to as “incidence side”). Light diffused by incidence plane diffusion parts 11 travels within light guide plate 4 and are emitted from light emission plane of light guide plate 4 while being reflected and refracted by the back and the light emission plane (plane opposite to liquid crystal panel 1) of light guide plate 4.
Further, reflection sheet 9 is disposed on the back of light guide plate 4, so that light passing through the back of light guide plate 4 and traveling toward chassis is reflected by reflection sheet 9 to be returned to light guide plate 4. Here, one reflection sheet 9 is disposed for one light guide plate 4. Reflection sheet 9 has holes formed in parts corresponding to places where light emitting diodes 7 are disposed and light emitting diodes 7 are put into grooves 6 through the holes from below (from chassis side). The upper surface (reflection surface) of reflection sheet 9 is disposed on the chassis side lower than lower end of light emission plane of light emitting diodes 7. Furthermore, it is desirable that transmissivity of reflection sheet 9 is smaller than or equal to 4% at maximum, so that light is diffused and reflected by reflection sheet with high efficiency.
As shown in
One to three out of the plurality of light emitting diodes 7 mounted on light source substrate 8 are defined to be one control unit and if intensity of light is controlled in accordance with brightness of image for each control unit, light intensity of backlight can be controlled partially, that is, area control can be performed. For example, 15 light emitting diodes are mounted on one light source substrate 8 and 2 light emitting diodes are defined to be one control unit. In addition thereto, if light source substrate 8 is also disposed in lower end of light guide plate 4, light guide plate 4 can be divided into 15 areas in the structure of
The reason that light source substrates 8 are separated without integrating them and are disposed in respective places corresponding to grooves 6 is that distance between light emitting diodes 7 and incidence planes in grooves 6 of light guide plane 4 is prevented from being changed when light guide plate 4 is expanded by heat from light emitting diodes 7. When distance between light emitting diodes 7 and incidence planes is changed, incidence efficiency of light from light emitting diodes 7 is changed largely and this causes unevenness in brightness. In the embodiment, in order to prevent it, light source substrates 8 are disposed in a corresponding manner to grooves 6. By constructed in this manner, since light source substrates 8 are also moved together with thermal expansion of light guide plate 4, distance between light emitting diodes 7 and incidence planes can be maintained to be fixed and occurrence of unevenness in brightness can be suppressed.
In the embodiment, as shown in
In the embodiment, in order to prevent the above deficiency, light traveling toward liquid crystal panel 1 from grooves 6 is diffused and reflected by the diffuse reflection members 5 and accordingly brightness of parts right above grooves 6 is reduced, so that unevenness in brightness can be reduced. In this example, the diffuse reflection members 5 are disposed on light emission plane of light guide plate 4, although the diffuse reflection members 5 may be disposed on inner side of grooves 6 right above light emitting diodes 7 and opposite to light emitting diodes 7. The diffuse reflection members 5 may be formed of white oblong plate-like sheet or film of resin extending in horizontal direction of the image display so as to cover grooves 6 from light emission plane side of light guide plate 4 and having surface subjected to roughening processing, for example.
In the embodiment, optical pattern 10 is provided on the side on light incidence side opposite to light emission plane of light emitting diodes 7 in grooves 6 and optical pattern 11 is provided on the side (hereinafter referred to as “side on back”) opposite to the back of light emitting diodes 7. Light incident to the sides is diffused or dispersed by optical patterns 10 and 11. The first pattern 10 and the second pattern 11 are described in detail with reference to
Since light guide plate 4 is formed into flat board having a fixed thickness except grooves as described above, light emitted with strongest intensity from light emitting diodes 7 disposed within a certain groove 6 travels straight within light guide plate 4 as shown in
On the other hand, first optical pattern 10 is formed on incidence side opposite to light emission plane of light emitting diodes 7 in groove 6. The provision of first optical pattern 10 can disperse light from light emitting diodes 7 with relatively short distance to be extended. Accordingly, spatial uniformity of light can be improved and unevenness in brightness can be more reduced. When light emitting diodes which emit light having colors different from one another instead of white light are used as light emitting diodes 7, the colors can be mixed with short distance by first optical pattern 10. As described above, first optical pattern 10 can disperse light from light emitting diodes 7 with short distance, so that it can be prevented parts between light emitting diodes 7 from being dark and unevenness in brightness can be still more reduced.
First and second optical patterns 10 and 11 are formed into prism array in
As shown in
The common point to
As described above, according to the embodiment, unevenness in brightness between light emitting diodes 7 can be reduced by first optical patterns 10 on the side on incidence side of grooves 6 and unevenness in brightness caused by the fact that light in optical axis direction of light emitting diodes 7 is absorbed in package on the back of light emitting diodes 7 disposed in next groove and increased temperature of light emitting diodes 7 can be suppressed. Therefore, according to the embodiment, unevenness in brightness in case where grooves are formed in light guide plate 4 and light emitting diodes 7 are disposed in grooves to construct the backlight can be reduced.
In the embodiment, grooves 6 extend in horizontal direction of the image display continuously as shown in
Moreover, diffuse reflection members 5 disposed in opposing relationship with grooves 6 on light emission plane of light guide plate 4 are not limited to the above structure and may be structured as modification example shown in
Further, minute pattern such as minute lenses as shown in
Furthermore, in the embodiment, white side-view type light emitting diodes may be used as light source, although point light source such as laser diode (LD) may be used or fluorescent lamp such as hot cathode fluorescent lamp (HCFL), cold cathode fluorescent lamp (CCFL) and external electrode fluorescent lamp (EEFL) may be used. Moreover, light source having plural colors as represented by red (R), green (G) and blue (B) to be mixed to get white light may be used except light source emitting white light. When white light emitting diodes are used, either YAG-W or RG-W may be used. Further, top-view type light emitting diodes which emit light in vertical direction to electrode plane thereof may be used. By using side-view type light emitting diodes as in the embodiment, even when cooling mechanism is provided in substrate although not shown, width of outside frame of backlight can be narrowed, so that the image display having narrow vessel, for example, can be realized. Moreover, package of light emitting diodes 7 may be made of ceramic or resin.
Further, light guide plate 4 is made of PMMA, polycarbonate, polystyrene, zeonor, BMC, OZ, silicone, glass or the like. Zeonor and polycarbonate can prevent moisture absorption and are difficult to cause deformation such as curve due to heat. Furthermore, two or more kinds of materials described above may be combined to form light guide plate. When light guide plate according to the embodiment is formed by molding, molding is performed with the draught taper for groove 6 set to be equal to or larger than 1 degree and smaller than 5 degrees.
Moreover, chassis 12 is made of aluminum, steel, magnesium or titanium alloy and is molded by pressing, die casting or scraping out. Further, chassis may be made of resin such as acryl, PMMA, zeonor, BMC, OZ, polycarbonate, polystyrene and silicone. Alternatively, 2 or more kinds of materials described above may be combined to form chassis.
In addition, optical sheet group 2 is composed of one or plural optical sheets, containing diffusion plates, diffusion sheets, micro-lens sheets, prism sheets, reflection type polarization films and the like, for example. One-dimensional pattern or two-dimensional pattern may be formed on surface of diffusion plates. Printing may be gradationally made on surface of diffusion plates or diffusion sheets by diffusion agent. One or both of sheets on which prisms are formed in longitudinal direction of backlight and sheets on which prisms are formed in short-side direction can be used as prism sheets. In this case, prism sheets having prisms formed thereon in longitudinal direction can be disposed on side of liquid crystal panel 1 to thereby widen viewing angle of the image display. On the other hand, prism sheets having prisms formed thereon in short-side direction can be disposed on side of liquid crystal panel 1 to thereby more improve central brightness of the image display.
One reflection sheet 9 is provided for one light guide plate 4, although construction between reflection sheet and light guide plate is not limited thereto and when plural light guide plates 4 are connected two-dimensionally, one reflection sheet 9 may be used for plural light guide plates 4 connected. When light guide plate 4 is divided into plural areas (optical control unit in area control), one reflection sheet 9 may be used in each area and one reflection sheet 9 having the same size as effective area of backlight or illumination device may be used.
As described above, according to the embodiment, unevenness in brightness in case where light from light emitting diodes is converted into surface light by means of light guide plate can be reduced. Therefore, according to the embodiment, there can be provided the backlight device capable of displaying image with high picture quality and the image display using the backlight device.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the scope of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2010-269876 | Dec 2010 | JP | national |
