Patent Application
20100141572
1. Field of the Invention
The present invention relates to an illumination device for use as a backlight of a display device and a display device using the same. In particular, the present invention relates to an illumination device and a display device that can achieve lower power consumption and high gray-scale image display by controlling the brightness of a backlight.
2. Description of the Related Art
In recent years, liquid crystal display devices characterized by low power consumption, thinness, and light weight have been widely used as display devices for a television. Such a liquid crystal display device includes a liquid crystal panel as a display element, which is a so-called non-luminous display element that does not emit light by itself. Thus, an illumination device called a backlight usually is provided on the back surface of the liquid crystal panel. The liquid crystal panel controls an amount of transmission light from the backlight to be transmitted through a number of pixels, each being a unit of image display, formed in a display region, thereby displaying an image.
Since each of the pixels of the liquid crystal panel only can block light to be transmitted therethrough as a shutter, the maximum amount of light to be transmitted through the pixel never exceeds the maximum amount of light emitted from the backlight. Under the circumstances, the backlight usually is designed to continue to always irradiate the whole display region of the liquid crystal panel with the maximum amount of light as a surface light source that irradiates light uniformly.
As a result, in the case where a black image is displayed in a large portion of the display region for a long time, for example, light that does not contribute to actual image display continues to be irradiated from the backlight only to be blocked by the liquid crystal panel, which is a waste of power for lighting the backlight. Further, since each of the pixels of the liquid crystal panel does not block transmission light with 100% reliability, a phenomenon called “backlight bleeding” occurs in which brightness is not decreased sufficiently when a black image is displayed, which leads to a lower contrast of an image to be displayed on the liquid crystal panel.
In order to solve the above-described problems, a so-called active-backlight-type backlight for use in the liquid crystal display device has been proposed that irradiates each of a plurality of regions obtained by dividing the display region with a necessary amount of light in accordance with a display image, rather than continuing to always irradiate the whole display region of the liquid crystal panel with light having the same brightness (JP 2001-142409 A).
As shown in
However, there still is a cost problem in using a large number of the package-type light-emitting diodes as used in the above-described conventional active backlight, although a per-unit price of the package-type light-emitting diodes recently is dropping because of the economies of volume production. Further, since a number of the light-emitting diodes are disposed in the limited region, the influence of heat generated from the respective light-emitting diodes is not negligible. More specifically, in the case where some of the light-emitting diodes emit light while the others do not for a relatively long time, an ambient temperature rises in a region surrounded by the light-emitting diodes that emit light, and accordingly may vary from an ambient temperature in a region surrounded by the light-emitting diodes that are extinguished. The variation in the ambient temperature of the light-emitting diodes has an influence on temperature characteristics of the light-emitting diodes, so that slightly different emission brightness is obtained by applying the same current, which may make it impossible to display an image accurately in each of the divided display regions.
In view of the above-described problems, preferred embodiments of the present invention provide a so-called active-backlight-type display device allowing irradiation brightness to be controlled individually for each of a plurality of divided display regions that enables a cost reduction of a light source and can display an image more accurately by eliminating an influence on temperature characteristics, and an illumination device suitable for use in this display device.
An illumination device according to a preferred embodiment of the present invention is an illumination device for use in a display device that is capable of irradiating each of a plurality of divided irradiation regions with an amount of light controlled individually. The device includes: a plurality of light sources that correspond one to one to the plurality of divided irradiation regions and whose number is the same as that of the divided irradiation regions; and a light transmission medium that transmits light emitted from each of the light sources to the divided irradiation region corresponding to the light source to irradiate the same. Brightness of the plurality of light sources is controlled individually, so that an amount of light irradiated onto each of the plurality of divided irradiation regions is controlled.
Further, a display device according to a preferred embodiment of the present invention includes: a display element that controls an amount of transmission light to be transmitted through pixels, thereby displaying an image in a display region; and an illumination device that irradiates each of a plurality of divided display regions obtained by dividing the display region with an amount of light controlled individually. The display device controls an amount of irradiation light from the illumination device for each of the divided display regions and transmittance of each of the pixels corresponding to the amount of irradiation light based on an input vide signal, thereby displaying an image. The illumination device includes: a plurality of light sources that correspond one to one to the plurality of divided display regions and whose number is the same as that of the divided display regions; and a light transmission medium that transmits light emitted from each of the light sources to the divided display region corresponding to the light source to irradiate the same. Brightness of the plurality of light sources is controlled individually, so that the amount of irradiation light is controlled.
According to various preferred embodiments of the present invention, it is possible to provide an illumination device that can achieve a cost reduction and control brightness accurately by eliminating non-uniform brightness caused by an ambient temperature variation, as an active-backlight-type illumination device allowing an amount of irradiation light to be controlled individually for each of divided irradiation regions. Further, when the illumination device according to one of the preferred embodiments of the present invention is used as an active-backlight-type backlight for a display element that controls an amount of transmission light to be transmitted through pixels, thereby displaying an image in a display region, it is possible to realize a display device that can achieve lower power consumption and prevent the backlight light source from being influenced in temperature characteristics by an ambient temperature, thereby displaying a high-quality image by accurate brightness control.
Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
An illumination device according to preferred embodiments of the present invention preferably is an illumination device for use in a display device that is capable of irradiating each of a plurality of divided irradiation regions with an amount of light controlled individually. The device includes a plurality of light sources that correspond one to one to the plurality of divided irradiation regions and whose number is the same as that of the divided irradiation regions, and a light transmission medium that transmits light emitted from each of the light sources to the divided irradiation region corresponding to the light source to irradiate the same. Brightness of the plurality of light sources is controlled individually, so that an amount of light irradiated onto each of the plurality of divided irradiation regions is controlled.
With this configuration, light is irradiated by the light transmission medium between each of the light sources and the divided irradiation region corresponding to the light source. This increases the degree of freedom in the locations of the light sources, and eases limitations on the number of the light sources. Therefore, it is possible to obtain an illumination device that can be applied suitably as a highly practical active-backlight-type backlight.
Further, in the above configuration, each of the light sources preferably is provided on a side wall of a light source box containing the light sources and the light transmission medium therein. Consequently, it is possible to prevent effectively a variation in temperature characteristics that is caused when an ambient temperature of each of the light sources rises by heat generated from other light sources surrounding the same.
Further, the light sources are preferably white light-emitting diodes. Consequently, it is possible to obtain a light source that can emit white light, which is most suitable as backlight light for a display element, and provide a sufficient amount of light with a small area. Light from this light source can be transmitted and irradiated onto the corresponding irradiation region easily by means of the light transmission medium.
Further, the light transmission medium is preferably an optical fiber. An optical fiber enables free design as to the length of a transmission path, the degree of bending, and the like, and has significantly excellent practicality as a high-efficiency light transmission medium.
Further, it is more preferable that the light transmission medium is a collection of a plurality of the optical fibers, which extend radially at an end portion on the divided irradiation region side. Consequently, light from each of the light sources can be transmitted and irradiated uniformly onto the divided irradiation region that has a larger area than a light-emitting surface of the light source.
Further, the light transmission medium may be a light guide that includes an optical member having a light diffusing effect on an end surface on the divided irradiation region side and has a constant diameter throughout its length.
Still further, a display device according to a preferred embodiment of the present invention includes a display element that controls an amount of transmission light to be transmitted through pixels, thereby displaying an image in a display region, and an illumination device that irradiates each of a plurality of divided display regions obtained by dividing the display region with an amount of light controlled individually. The display device controls an amount of irradiation light from the illumination device for each of the divided display regions and transmittance of each of the pixels corresponding to the amount of irradiation light based on an input vide signal, thereby displaying an image. The illumination device includes a plurality of light sources that correspond one to one to the plurality of divided display regions and whose number is the same as that of the divided display regions, and a light transmission medium that transmits light emitted from each of the light sources to the divided display region corresponding to the light source to irradiate the same. Brightness of the plurality of light sources is controlled individually, so that the amount of irradiation light is controlled.
With this configuration, the amount of irradiation light required for displaying an image in each of the divided display regions and the transmittance of each of the pixels are obtained based on the video signal. Therefore, it is possible to obtain a display device that includes an active-backlight-type illumination device that is highly effective in achieving lower power consumption and can display a high-quality image with uniform display brightness.
In implementing the display device according to various preferred embodiments of the present invention, by adopting various preferable aspects of the above-described illumination device according to preferred embodiments of the present invention, it is possible to obtain a display device that can perform more preferable image display.
Hereinafter, preferred embodiments of an illumination device and a display device using the same according to preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the display device according to various preferred embodiments of the present invention is exemplified by a liquid crystal display device for a television that includes a transmission type liquid crystal display element, and the illumination device according to preferred embodiments of the present invention is used as a backlight of the display device. However, applications of the present invention are not limited thereto. For example, a semi-transmission type liquid crystal display element can be used as a display element of the display device according to the present invention. Further, the display device according to the present invention is not limited to the liquid crystal display device for a television, but can be used as an information display monitor for use in public institutions such as a station and a museum, a computer monitor required to have a large screen, and the like.
The liquid crystal panel 1 is a transmission type liquid crystal display element that controls an amount of transmission light to be transmitted through pixels, thereby displaying an image. The type of the liquid crystal panel 1 is not limited particularly as long as multi-gray-scale image display is possible, and may be either an active matrix type using a switching element such as a TFT or a simple matrix type. Further, the liquid crystal panel 1 may be of any of various liquid crystal display modes such as a vertically-aligned (VA) mode type, an IPS type, and an OCB type. In a central portion of the liquid crystal panel 1 other than a peripheral portion where a sealing portion, a circuit for displaying an image, a terminal portion for supplying a voltage to the liquid crystal panel 1, and the like are formed, a display region 6 in which pixels for displaying an image are formed is provided. As shown in
In the example shown in
The backlight unit 2, which irradiates the display region 6 of the liquid crystal panel 1 with light from the light sources to be described later, can control an amount of irradiation light for each of the above-described divided display regions 6a of the liquid crystal panel 1. In
Next, the following description is directed to signal processing for image display in the display device according to the present preferred embodiment. As shown in
Based on the amount of irradiation light to be irradiated onto each of the divided display regions 6a determined based on the above-described brightness control signal, the image control signal determines the level of gray-scale to be assigned to a pixel included in the corresponding divided display region 6a. Namely, the image control signal controls transmittance in each pixel. As described above, in the display device according to the present preferred embodiment, the amount of irradiation light to be irradiated from the backlight unit 2 onto each of the divided display regions 6a always varies. Thus, unless each pixel is assigned with transmittance corresponding to the amount of irradiation light, the amount of transmission light in the pixel cannot be controlled accurately. For this reason, even if the amount of transmission light in each pixel as one luminescent spot for image display is the same, the gray-scale signal for determining transmittance in the pixel is different when the amount of light irradiated from the backlight unit 2 varies.
The image control signal is input to the gray-scale control circuit 12 as an image signal with gray-scale information that accommodates active backlight display of a preferred embodiment of the present invention, and is divided into a horizontal driving signal and a vertical driving signal, so that one image can be displayed by scanning in the vertical and horizontal directions. The horizontal driving signal and the vertical driving signal drive the horizontal driving circuit 14 and the vertical driving circuit 15, respectively. The vertical and horizontal scanning for image display is performed in the same manner as that for driving a liquid crystal panel using a usual backlight that always irradiates light having uniform brightness unlike the active backlight type. The liquid crystal panel according to the present preferred embodiment is driven in a manner different from that of the conventional liquid crystal panel only in that the gray-scale signal assigned as described above corresponds to the amount of light from the backlight.
The brightness control signal is input to the brightness control circuit 13, and in order to obtain the amount of irradiation light to be irradiated onto each of the plurality of divided display regions 6a, the brightness control circuit 13 generates a light source driving signal for adjusting the brightness of the light source corresponding to each of the divided display regions 6a to irradiate light thereon. The light source driving signal is input to the light source driving circuit 16, and the light source driving circuit 16 controls a voltage or current to be applied to each of the light sources in the backlight unit 2 individually, so that the light source emits light having desired brightness at a desired timing to irradiate a necessary amount of light.
In this manner, the active backlight type according to the present preferred embodiment makes it possible to reduce the amount of irradiation light from the backlight in a portion that does not contribute to image display, thereby achieving lower power consumption of the backlight unit. Further, in the case of the active backlight type, it is highly likely that the amount of irradiation light from the backlight unit 2 can be suppressed in the divided display region 6a that is required to display a black image. Thus, a phenomenon so-called a “backlight bleeding”, which is caused due to an inevitable leakage of light in each pixel of the liquid crystal panel 1, can be minimized and prevented. Therefore, by using the active backlight type, it is possible to achieve high gray-scale image display on the liquid crystal panel, as well as to reduce power consumption for lighting the backlight.
Next, the configuration of the backlight unit 2 in the display device according to a preferred embodiment of the present invention will be described with reference to
Although not shown in the figure, the liquid crystal panel 1, which preferably is a transmission type active matrix liquid crystal element, includes a liquid crystal layer sandwiched between two glass substrates sealed together. In the central portion of the liquid crystal panel 1, the display region 6 in which a number of pixels for displaying an image are arranged in a matrix is formed. As shown also in
The backlight unit 2 includes a bottomed frame 5, white light-emitting diodes 4 as light sources fixed to short-side side walls of the frame 5, and optical fibers 3 as a light transmission medium that transmit light emitted from each of the white light-emitting diodes 4 to irradiate the corresponding divided display region 6a therewith. Since the white light-emitting diodes 4 as light sources correspond one to one to the divided display regions 6a, the number of the white light-emitting diodes 4 in the display device of the present preferred embodiment is the same as that of the divided display regions 6a, i.e., twelve.
Next, the white light-emitting diodes 4 as light sources and the optical fibers 3 as a light transmission means will be described in more detail with reference to
As shown in
One end portion 3d of the optical fibers 3 is arranged so as to be opposed to a light-emitting surface 4a of the white light-emitting diode 4. Each of the optical fibers 3 according to the present preferred embodiment is a so-called power transmission fiber that transmits at least light in a visible light region and uses quartz glass as a core material, and has a diameter of about 1 mm in cross section. From the one end portion 3d of the optical fibers 3 opposed to the light-emitting surface 4a of the white light-emitting diode 4 to an intermediate portion 3c, the plurality of optical fibers 3 are held in a bundle. However, at the other end portion of the optical fibers 3, i.e., an end portion 3b on a side of the divided display region 6a to be irradiated with light, the optical fibers 3 extend radially as shown in
Further, as shown in an enlarged view in
It is preferable that the optical fibers 3 extend radially at the end portions 3b on the divided display region 6a side such that vicinities of the end surfaces 3a of the optical fibers 3 on the divided display region 6a side are perpendicular or substantially perpendicular to the divided display region 6a as shown in
As described above, the white light-emitting diodes 4 capable of controlling brightness on its own are used in the active-backlight-type backlight unit, and light irradiated from each of the white light-emitting diodes 4 is transmitted through the optical fibers 3 as a light transmission medium so as to be irradiated onto the corresponding divided display region 6a. Thus, the light sources, which conventionally have been required to be arranged directly behind the back surface of the divided display regions 6a, can be disposed as appropriate in any portion other than directly behind the back surface of the divided display regions 6a. Consequently, it is possible to realize an active-backlight-type backlight unit that can irradiate each of the divided display regions 6a with light having predetermined brightness by solving the problem of the conventional backlight unit 2 that the light-emitting diode as a light source varies in temperature characteristics under the influence of heat radiated from other surrounding light-emitting diodes, so that brightness cannot be controlled at a predetermined value.
In
In the present preferred embodiment, the white light-emitting diodes as light sources are preferably provided on the short-side side walls of the backlight unit. However, the display device and the illumination device for use in the display device according to the present invention are not limited thereto. They may be provided not only on the short-side side walls but also on long-side side walls, or may be provided on the bottom of the light source box, i.e., on a surface on the back surface side of the liquid crystal panel. In any case, since the backlight unit of various preferred embodiments of the present invention includes the light transmission medium for directing light from the light sources to the divided display regions, there is no such limitation that the light sources should be disposed directly behind the back surface of the divided display regions. Thus, it is possible, for example, to locate the light sources so that heat therefrom does not remain in view of the structure of the backlight, to adjust the space between the light sources so as to prevent each of the light sources from being influenced by heat generated from the adjacent light sources, and to provide a mechanism for dissipating heat to the outside such as a cooling fin and a heat dissipating fan, so as to concentrate the light sources in the vicinity thereof.
Next, a second preferred embodiment of the display device according to the present invention will be described with reference to
As shown in
As shown in
As shown in
Further, on the end surface 10b of the light guide 10 on the white light-emitting diode 4 side, a member having a so-called optical coupling effect may be applied by, for example, covering a gap between the light-emitting surface 4a of the white light-emitting diode 4 and the end surface 10b of the light guide 10 with transparent resin, thereby allowing light emitted from the white light-emitting diode 4 to be incident on the light guide 10 more efficiently.
The description has been given of the preferred embodiments of the display device according to the present invention particularly with respect to the configuration of the backlight unit. However, the present invention is not limited to these specific examples. For example, the white light-emitting diode is used as a light source in the above-described preferred embodiments because the light-emitting diode is appropriate in terms of responsiveness to the brightness control signal and the amount of irradiation light. Accordingly, another light source such as an EL element, a discharge element, and a fluorescent tube is also available, as long as it can respond to the brightness control signal sufficiently and produce a sufficient amount of irradiation light. Further, the white light-emitting diode is used because color display on the liquid crystal panel usually requires a white light source and color filters of three colors of RGB formed in the liquid crystal panel. Accordingly, the light source is not necessarily limited to the white light source when used in a display device that does not perform color display, or depending on the combination with colors of the color filters formed in the liquid crystal panel even when used in a display device that performs color display. Needless to say, light of a necessary color may be irradiated as appropriate.
Further, in order to ensure and improve the uniformity of the amount of irradiation light in the divided display region, an optical diffuser having a function of scattering irradiation light or the like may be provided between the end portion of the light transmission medium on the light emission side and the divided display region. The light diffuser in this case can be a diffuser to be provided between a usual direct-type backlight light source and a liquid crystal panel in a liquid crystal display device.
The present invention is industrially applicable as an illumination device usable as an active-backlight-type backlight that is suitable for achieving lower power consumption of a display device and higher gray-scale image display, and a display device using the illumination device.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-112263 | Apr 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/057433 | 4/16/2008 | WO | 00 | 10/13/2009 |
