Illumination – Revolving
Reexamination Certificate
2001-05-30
2004-01-06
Flynn, Nathan J. (Department: 2812)
Illumination
Revolving
Reexamination Certificate
active
06672733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a backlight unit having a color adjusting function and a liquid crystal display device having backlight units.
2. Description of the Prior Art
The liquid crystal display device has such a merit that the device is thin in thickness, is light in weight, is driven by a low voltage, and needs small power consumption. Thus, the liquid crystal display device is extensively employed in various electronic devices.
In particular, the active-matrix type liquid crystal display device in which active elements such as TFTs (Thin Film Transistors) are provided every pixel is excellent such that the device is equivalent to the CRT (Cathode-Ray Tube) in the respects such as the luminance, the viewing angle characteristic, etc. Therefore, recently the liquid crystal display device of this type is also employed as the display device for the mobile television, the personal computer, etc.
Normally the backlight units are incorporated into the liquid crystal display device on the back surface side of the liquid crystal display panel. The transmittance of lights that are emitted from the backlight units is controlled every pixel constituting the liquid crystal display panel to display the image.
FIG. 1
is a sectional view showing a configuration of the liquid crystal display device including the backlight unit in the prior art.
The backlight unit has a light guide plate
61
, white color fluorescent tubes
63
arranged on both longitudinal sides of the light guide plate
61
respectively, and reflectors
62
for reflecting the lights that are emitted from these fluorescent tubes
63
toward the light guide plate
61
respectively. The backlight unit is installed in a casing
69
. A reflection sheet
66
is arranged on the back surface side of the light guide plate
61
, and a diffusion sheet
64
and a prism sheet
65
are laminated to be arranged on the front surface side.
A liquid crystal panel
67
is placed over the prism sheet
65
, and is fitted to the casing
69
by using a metal bezel
68
.
In the liquid crystal display device constructed in this manner, the lights emitted from the fluorescent tubes
63
enter into the light guide plate
61
directly or after they are reflected by the reflectors
62
. The incident lights into the light guide plate
61
can propagate through the light guide plate
61
while reflecting repeatedly between an upper surface and a lower surface of the light guide plate
61
. The lights that exceed a critical angle are emitted from the light guide plate
61
to the liquid crystal panel
67
. The lights that are emitted from the light guide plate
61
are diffused by the diffusion sheet
64
and the prism sheet
65
such that the direction of the light is regulated, and then reach the liquid crystal panel
67
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a backlight unit having a color adjusting function to itself and a liquid crystal display device having backlight units.
In order to achieve the above object, there is provided a backlight unit of the present invention comprising a plurality of light sources whose luminescent chromaticities are different mutually, said plurality of light sources including at least one white color light source; and a light guide plate for receiving lights emitted from said plurality of light sources and emitting the lights to a predetermined direction.
According to the above configuration, in the backlight unit of the present invention, a plurality of light sources whose luminescent chromaticities are different mutually are provided to give a color adjusting function to the unit itself, and the luminances of respective light sources are controlled independently by the control voltages supplied from external devices. For example, since the white color fluorescent tube, the red color fluorescent tube, the green color fluorescent tube, and the blue color fluorescent tube are provided as the light sources, the lights emitted from the light guide plate can be controlled into the desired color.
In this case, since the white color fluorescent tube is provided, the magnitude of the influence upon the luminance change and the color change caused when a quantity of the lights emitted from the red color fluorescent tube, the green color fluorescent tube, and the blue color fluorescent tube are changed independently can be relaxed and adjusted by the luminance level of the white color fluorescent tube.
Such backlight unit is arranged on the back surface side of the liquid crystal panel, and the liquid crystal display device that is able to display the image having the excellent color reproducibility can be obtained.
REFERENCES:
patent: 5976686 (1999-11-01), Kaytor
patent: 6196691 (2001-03-01), Ochiai
patent: 7-301797 (1995-11-01), None
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Stevenson André C.
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