JP2001255507A - Backlight for color liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight for color liquid crystal display device where no color unevenness is generated, even if a red (R) light source is formed by using a cold-cathode tube. SOLUTION: A mixture of colors, formed by mixing a red color with the other color, is prevented more surely, even if the red (R) light source is formed by using the cold cathode tube, since lighting-off timing of the red (R) light source is set earlier, taking into consideration afterglow of the red beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a backlight for a color liquid crystal display.

[0002]

2. Description of the Related Art Recently, OA of personal computers and the like has been developed.
2. Description of the Related Art A color liquid crystal display device is used for a display of a home appliance such as a device or a television. As this type of color liquid crystal display device, a TFT type color liquid crystal display device is widely known. In the TFT type, a clear full-color image can be obtained, but a color filter and a thin film transistor are provided for each pixel (liquid crystal cell). Because of the necessity, very fine processing is required for manufacturing the liquid crystal cell, and there are also problems such as difficulty in adjusting the color balance.

Therefore, as an alternative to the TFT method,
A color filter-less color liquid crystal display device that does not require a color filter or a thin film transistor and combines a monochrome liquid crystal cell with three primary color backlights has been proposed (see, for example, JP-A-7-281647). That is, the light sources of the three primary colors are pulsed sequentially and periodically,
By opening the liquid crystal at the same timing as the color of the emitted light, it is possible to obtain afterimage color mixture by a combination of red (R), green (G), and blue (B).

[0004] As a backlight used in this filterless color liquid crystal display device, a reflector having a U-shaped cross section opened at one end face of one light guide plate is provided at one end face thereof. It has a structure in which three light sources of red (R), green (G), and blue (B) are arranged in a reflecting mirror. The three light sources are tubes of the same diameter, two of the green (G) light source and the blue (B) light source are formed of cold cathode tubes, and the red (R) light source is formed of a rare gas discharge tube. The reason why only the red (R) light source is formed by a rare gas discharge tube is that if the red (R) light source is a cold cathode tube, the afterglow of red becomes longer and overlaps with other colors, causing color unevenness. That's why.

[0005]

However, the rare gas discharge tube used for the red (R) light source has a higher lighting voltage than the cold cathode tube and a larger inverter for the same, so that cost is reduced. Disadvantageous. Therefore, there is a demand for a proposal of a new technique that does not cause color unevenness even if the red (R) light source is formed by a cold cathode tube.

The present invention has been made by paying attention to such a conventional technique. Even if a red (R) light source is formed by a cold cathode tube, a back for a color liquid crystal display device in which color unevenness does not occur. It provides light.

[0007]

According to the first aspect of the present invention,
A light guide plate is provided at one end face thereof with a reflector having a sectional shape open to the one end face side, and a light source of an independent cold-cathode tube of three primary colors which sequentially and periodically emits a pulse in the reflector is provided. A backlight for a color liquid crystal display device arranged side by side in a plane direction of a light plate, wherein a turn-off timing of a red (R) light source among the three primary color light sources is advanced to reduce a lighting pulse time of the red (R) light source. A control circuit for shortening is provided.

According to the first aspect of the present invention, red (R)
In consideration of the afterglow, the turning off timing of the red (R) light source is advanced, so that even if the red (R) light source is formed by a cold cathode fluorescent lamp, the red (R) light and other colors Color mixing is more reliably prevented.

According to the second aspect of the present invention, the tube current of the red (R) light source is higher than that of the other light sources.

According to the second aspect of the present invention, red (R)
Since the tube current of the light source is higher than that of the other light sources, it is possible to compensate for the decrease in brightness due to the earlier turn-off timing. Moreover, even if the tube current of the red (R) light source is increased, the turn-off timing is advanced, so that the life of the tube of the red (R) light source is not different from other tubes.

According to the third aspect of the present invention, the red (R) light source is turned off 2.6 ms earlier than the other light sources.

According to the third aspect of the present invention, red (R)
By turning off the light source 2.6 ms earlier than the other light sources, the red afterglow is reduced to about 10% when the other light source is turned on, so that the influence of the afterglow can be reliably eliminated.

According to the fourth aspect of the present invention, halftone dots are provided in a dot pattern on the back surface of the light guide plate, and the areal density of the halftone dots increases as the light amount attenuates.

According to the fourth aspect of the present invention, since the area density of the halftone dots provided on the back surface of the light guide plate increases as the light amount attenuates, the reflection in the range where the luminance is easily attenuated. Efficiency is increased and luminance can be made uniform.

According to a fifth aspect of the present invention, light diffusing means is provided on the surface of the light guide plate.

According to the fifth aspect of the invention, the light emitted from the front side of the light guide plate is diffused by the diffusion means to become scattered light, so that the light source itself and the halftone dot pattern cannot be directly seen. The effect that the entire surface shines uniformly is obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to FIGS. Note that, in FIG.
Is the surface direction, arrow Y is the thickness direction, the upper side is the front side, and the lower side is the back side.

Reference numeral 1 in the drawing denotes a backlight used in a filterless color liquid crystal display device, and a liquid crystal cell (not shown) is provided on the surface side thereof. This liquid crystal cell is a known liquid crystal cell in which liquid crystal (STN) is sealed between two glass substrates and the liquid crystal is turned on and off via a transparent conductive film (ITO film) arranged in a matrix. This liquid crystal cell can be used for monochrome,
Since no color filter or thin film transistor is required, the structure is simple.

The backlight 1 includes one light guide plate 2, a reflecting mirror 3, three light sources 4, 5, 6, a diffusion sheet (diffusion means) 7, a halftone dot (dot pattern) 8, , And a reflection sheet 9.

As the light guide plate 2, a transparent resin plate or a molded product having six smooth surfaces can be used. As the transparent resin, an acrylic plate, a polyester plate, a vinyl chloride plate and the like are preferable. The cross-sectional area (that is, the thickness) of one end face (light incident face) of the light guide plate 2 is an important factor for effectively introducing light from the light sources 4, 5, and 6, and the larger the size in the thickness direction Y, the larger the size. Efficiency is high and a large amount of light can enter the light guide plate 2. However, if it is too thick, it takes up space, which is against the weight and size reduction of the electronic device, and also leads to light loss. Since the backlight 1 of this embodiment requires only one light guide plate 2, it is advantageous in that the structure is simple and the device is reduced in size and thickness.

Printed on the back surface of the light guide plate 2 are white dots 8. The halftone dots 8 are for scattering light, and are formed by printing an ink in which a filler having a high refractive index is mixed with an organic resin in a dot shape. This dot 8
The surface density increases as the distance from the light sources 4, 5, 6 and the reflection sheet 9 increases (as the position approaches the center position), contributing to the uniformity of luminance. It should be noted that the halftone dots 8 have essentially no thickness, but are shown with a certain thickness in the figure for easy understanding.

The reflecting mirror 3 is mounted on one end face of the light guide plate 2. The reflecting mirror 3 has a cross-sectional curved shape (a U-shaped cross section) opened on one end surface side. All the inner surfaces of the reflecting mirror 3 efficiently transmit light from the light sources 4, 5, and 6 to the light guide plate 2.
It is a silver mirror surface with high reflectivity so that it is introduced into the inside and does not leak to the outside.

The reflection sheet 9 is a sheet made of a white high-reflectance material, on which a metal film such as aluminum or silver is adhered by vapor deposition or the like. A metal tape such as aluminum or silver may be adhered to the side surface.

Light emitted from the surface of the light guide plate 2 passes through the diffusion sheet 7. The light passing through the diffusion sheet 7 becomes scattered light due to minute irregularities and satin patterns on the surface, so that the light sources 4, 5, and 6 themselves and the pattern of the halftone dots 8 are not directly seen, and an effect of uniformly illuminating the entire surface is obtained. Can be

The red (R) light source 4
Is disposed closest to the light guide plate 2 and the green (G) light source 5
Are arranged second, and the blue (B) light source 6 is arranged third on the innermost side. And all three are cold cathode tubes.

The color light emitted from the light sources 4, 5 and 6 is incident on the light guide plate 2 from the end face of the light guide plate 2 directly or after being reflected by the reflecting mirror 3. The light that has entered the light guide plate 2 hits a halftone dot 8 and is scattered, so that the light is reflected toward the surface of the light guide plate 2. Light emitted from the surface of the light guide plate 2 is diffused by the diffusion sheet 7 and then reaches a liquid crystal cell (not shown), where a color liquid crystal display can be performed.

Next, a lighting circuit of the backlight 1 will be described with reference to FIG. The green (G) and blue (B) signal generation circuits 10 and the red (R) signal generation circuit 11 generate a pulse waveform signal of each color. The three light sources 4, 5, and 6 in the backlight 1 are connected to the control circuit 14 via the corresponding inverters 11, 12, and 13, respectively. Reference numeral 15 denotes a power supply.

FIG. 3 shows the tube current of each of the light sources 4, 5, and 6, and FIG. 4 shows the tube current of only the red (R) light source 4. Each of the light sources 4, 5, and 6 has a pulse waveform in which the duty is set to 1/3, and the pulse rises in a form shifted by exactly 1/3 period. However, in this embodiment, the control circuit 14
1. Only the pulse of the red (R) light source 4 is higher than other pulses.
The light is turned off as early as 6 ms, and the lighting pulse time of the red (R) light source 4 is shortened. FIG. 5 is a graph showing the light-on (light-off) timing. It can be seen from this graph that the red (R) light source 4 is turned off quickly. Therefore, the afterglow of the red (R) light source 4 does not reach the range of the next green (G) light source 5. The turning off timing of the red (R) light source 4 is 2.6 m
If s is advanced, when the green (G) light source 5 rises, the afterglow is reduced to about 10%, and the effect is eliminated. Further, in this embodiment, as is apparent from FIG. 4, the current of the red (R) light source 4 is higher than the levels of the other green (G) and blue (B) light sources 5 and 6. This makes it possible to compensate for the decrease in brightness due to the earlier turn-off timing of the red (R) light source 4. Moreover, even if the tube current of the red (R) light source is increased,
Since the turn-off timing is advanced, the life of the tube of the red (R) light source is not different from that of other tubes.

[0029]

According to the present invention, since the turning off timing of the red (R) light source is advanced in consideration of the afterglow of red in advance, even if the red (R) light source is formed by a cold cathode tube. Therefore, the mixing of red and other colors is more reliably prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a backlight for a color liquid crystal display device of the present invention.

FIG. 2 is an exploded perspective view showing the backlight of FIG. 1;

FIG. 3 is a view showing a tube current waveform of the light source shown in FIGS.

FIG. 4 is a view showing a tube current waveform of the red (R) light source of FIG. 3;

FIG. 5 is a diagram showing lighting (turning off) timing of a light source.

FIG. 6 illustrates a lighting circuit of a light source.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 backlight 2 light guide plate 3 reflecting mirror 4 red (R) light source 5 green (G) light source 6 blue (B) light source 7 diffusion sheet (diffusion means) 8 halftone dot 9 reflection sheet 14 control circuit X plane direction Y thickness direction

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 642 G09G 3/34 J 3/34 3/36 3/36 F21W 101: 14 // F21W 101 : 14 F21Y 103: 00 F21Y 103: 00 113: 00 113: 00 G02F 1/1335 530 F term (reference) 2H091 FA14Z FA23Z FA31Z FA42Z FB02 FC02 FD04 FD22 FD24 GA11 LA15 LA18 2H093 NC42 NC43 ND09 ND17 ND24 NE06 NF13 A11A11A AF44 AF78 BB14 EA01 FA00 FA56 5C080 AA10 BB06 CC03 DD05 EE30 FF01 FF09 JJ02 JJ04 JJ06 5G435 BB12 BB15 CC12 DD09 EE27 EE30 FF03 FF06 FF08 GG24 GG26 GG27

Claims (5)

[Claims] An independent cold cathode of three primary colors is provided on one end surface of one light guide plate with a reflecting mirror having a sectional shape opened on the one end surface side, and sequentially and periodically emitting light in the reflecting mirror. A backlight for a color liquid crystal display device, wherein a light source of a tube is arranged side by side in a plane direction of a light guide plate, wherein a turning off timing of a red (R) light source is accelerated among the three primary color light sources, and A backlight for a color liquid crystal display device, comprising a control circuit for shortening the lighting pulse time. 2. The color liquid crystal display device according to claim 1, wherein the tube current of the red (R) light source is higher than that of the other light sources. For backlight. 3. The backlight for a color liquid crystal display device according to claim 1, wherein the red (R) light source is turned off 2.6 ms earlier than other light sources. Backlight for color liquid crystal display devices. 4. The backlight for a color liquid crystal display device according to claim 1, wherein a halftone dot is provided in a dot pattern on a back surface of the light guide plate, and A backlight for a color liquid crystal display device, wherein the areal density is increased in a range where the light amount is attenuated. 5. The backlight for a color liquid crystal display device according to claim 1, wherein a light diffusing means is provided on a surface of the light guide plate. Backlight for liquid crystal display.