JP2002169153A - Illumination device for liquid crystal for color display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination device for a liquid crystal for color display which uses white light as the light source and which maintains proper white balance of the reproduced light reflected by the hologram of a light guide plate. SOLUTION: The illumination device of a liquid crystal display device has a light guide plate and illuminates the liquid crystal for color display with a light, reflected by the hologram formed on the reflection face of the light guide plate. The illumination device is provided with a light source, which uses LEDs of three colors of red, green and blue and mixes the lights emitted from the LEDs of three colors, to produce white light, and with a light guide plate having a hologram which reflects the light of wavelengths near the wavelengths of the red, green and blue color light from the light source with higher efficiency than the lights of other wavelengths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminating device for illuminating a color display liquid crystal, and more particularly to illuminating a color display liquid crystal with white light to change the color of characters and images displayed on the color display liquid crystal. The present invention relates to a color display liquid crystal lighting device that reproduces accurately.

[0002]

2. Description of the Related Art An illuminating device for illuminating a color display liquid crystal has a light source composed of a white LED (light emitting diode) and a light guide plate on which a hologram is formed as a reflection surface. There is a lighting device that projects and illuminates a color display liquid crystal. Since this lighting device has low power consumption and can be made very light and thin,
It is widely used in portable small electronic devices such as mobile phones.

However, as shown in FIG. 5, a white LED is formed on a blue LED 52 formed on a
An AG fluorescent layer 53 is formed, and a part of the blue light projected from the blue LED 52 excites the YAG fluorescent layer 53 to cause the YAG fluorescent layer 53 to emit light yellow. The blue light emitted from the blue LED 52 is mixed with light yellow, which is a complementary color emitted from the YAG fluorescent layer 53, to produce white light. Therefore, as shown in FIG. 6, the distribution of the light intensity with respect to the wavelength of the white light has a blue peak A and a pale yellow peak B, which are reflected on the hologram surface of the light guide plate. It is known that the reproduction light loses color balance (white balance) and becomes dull green or bluish purple.

In order to correct this white balance, the hologram must be a hologram that maximizes the diffraction efficiency of red (wavelength of about 620 nm) light. In this case, light of a wavelength other than red is used. The diffraction efficiency of the hologram, the intensity of the light reflected on the hologram surface decreases as a whole, the amount of light illuminating the color display liquid crystal decreases, and the illumination light illuminating the color display liquid crystal darkens. That is inevitable. It is known from the characteristics of the hologram that if the wavelength of the reproduction reference light is different, the reproduction light will be blurred. Has two peaks, blue and pale yellow, so that blur occurs between the blue light and the pale yellow light, making it difficult to maintain a good overall white balance. .

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a hologram formed on a reflection surface of a light guide plate in a color display liquid crystal lighting device using white light as a light source. It is an object of the present invention to provide a lighting device for a color display liquid crystal capable of maintaining a good white balance of the reproduction light reflected by the LCD.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention has a light guide plate, and the color reflected by the hologram formed on the reflection surface of the light guide plate. In a lighting device for a liquid crystal display device that illuminates a display liquid crystal, an LED that emits light of three colors, red, green, and blue, is used, and a light source that mixes light emitted from the three colors of LEDs to produce white light. A light guide plate formed with a hologram that reflects light of wavelengths close to the wavelengths of red, green and blue light of the light source with higher efficiency than light of other wavelengths. A liquid crystal lighting device is provided.

Here, a hologram that reflects light of wavelengths close to the wavelengths of the three colors of red, green and blue of the light source with high efficiency is formed by the hologram of the three colors of red, green and blue of the light source. It is desirable that the hologram is a hologram that is multiple-exposed by lasers of three colors, red, green and blue, each having a wavelength close to the wavelength.
An LED that emits light of three colors of green and blue emits light of a wavelength approximating the wavelength of light of the laser of three colors of red, green and blue that exposes the hologram. It is desirable to select and employ LEDs. Further, the light source emits light of three colors of red, green and blue, and the plurality of LEs of the predetermined type are provided.
It is desirable to inspect the group of D and individually select and use only LEDs that emit light having a wavelength close to the wavelength of the laser light of the three colors red, green and blue that expose the hologram. .

Alternatively, a hologram in which light having a wavelength close to the wavelengths of the three colors of red, green and blue of the light source is reflected with higher efficiency than light of other wavelengths is a hologram having the three colors of red, green and blue. The hologram is formed so as to have the maximum efficiency at each wavelength of the laser of the laser light source, and the white balance is determined by adjusting the IF current and the luminance of each of the LEDs in the light source, which emits red, green and blue light. It is desirable to adjust by selecting and employing a rank.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing embodiments. FIGS. 1 to 3 are schematic views showing an example of a liquid crystal display device employing the color display liquid crystal lighting device of the present invention. FIG. 1 is a transmission type liquid crystal display device using a backlight, and FIG. FIG. 3 shows an example of a transflective liquid crystal display device using a light, and FIG. 3 shows an example of a reflective liquid crystal display device using a front light.

In each of these liquid crystal display devices, light projected from a light source 10 is diffused by a light guide plate 11 and projected as illumination light toward a liquid crystal display panel 12. 10. A transmissive or semi-transmissive liquid crystal display device (FIGS. 1 and 2) in which an illuminating device including a light guide plate 11 and the like is provided on the back side of the liquid crystal display panel 12, and illuminates as a backlight. There is a reflective liquid crystal display device (FIG. 3) which is on the back side of the liquid crystal display panel 12 and illuminates as a front light. Transmissive liquid crystal display using only light (Fig. 1)
There is a transflective liquid crystal display device that illuminates with the brightness of the external light when the external light is sufficiently bright, and turns on the backlight when the brightness is insufficient, and illuminates with the backlight.

Since the basic structure of the liquid crystal display panel 12 is the same in any of the liquid crystal display devices, the structure of the liquid crystal display panel 12 will be described here. As is well known, the liquid crystal display panel 12 basically has a structure in which a liquid crystal 15 is sandwiched between two glass substrates 13 and 14, and in this embodiment, is a color display liquid crystal. A color filter 16 is arranged below the glass substrate 13. Then, TF is provided on the upper surface of the lower glass substrate 14.
A T surface 17 is formed.

In a transmissive liquid crystal display device using a backlight shown in FIG. 1, polarizing plates 18 and 19 are disposed above and below the liquid crystal display panel 12, and the backlight is formed below the liquid crystal display panel 12. A light source 10, a light guide plate 11, and a light-condensing sheet or a diffusion sheet 20 for preparing light projected from the light guide plate 11 toward the liquid crystal display panel 12 are arranged.

A transflective liquid crystal display device using the backlight shown in FIG. 2 reflects light transmitted through the liquid crystal display panel 12 when external light is used as illumination light, and uses the backlight when the backlight is used. A half mirror 21 that transmits light projected from the light guide plate 11 toward the liquid crystal display panel 12 includes:
It is arranged between the polarizing plate 19 on the lower side of the liquid crystal display panel 12 and the condensing sheet or diffusion sheet 20 of the lighting device.

Further, in the reflection type liquid crystal display device using the front light shown in FIG. 3, a light source 10 and a light guide plate 11 constituting the front light are arranged above a liquid crystal display panel 12, and the light guide plate 11 and the liquid crystal A polarizing plate 23 having a compensation function of polarizing and adjusting light projected toward the liquid crystal display panel 12 is disposed between the display panel 12 and the display panel 12. Further, a reflection film 22 is formed on the upper surface of the lower glass substrate 14. The reflection film 22 reflects illumination light (including external light) projected from above, and may be provided as a reflection plate below the lower glass substrate 14.

Here, in this embodiment, the light guide plate 11
(In the embodiment of FIGS. 1 and 2, the upper surface of the light guide plate 11, and in the embodiment of FIG. 3, the lower surface) reflects light projected from the light source 10 and incident on the light guide plate 12. In order to project the light toward the liquid crystal display panel 12, a reflection surface by a hologram is formed. The reflection surface of the hologram is formed by forming a hologram on the reflection surface of the light guide plate 12 or attaching a sheet on which the hologram is formed.
When the light that diffuses and propagates inside 2 reaches the reflective surface,
The light is diffracted by the hologram, and the reproduced light is projected toward the liquid crystal display panel 12, and can be reflected with a uniform light amount over the entire reflecting surface. Therefore, the term “reflected by a hologram” in this specification means “diffraction by a hologram and projecting reproduction light toward the liquid crystal display panel 12”.

However, as described above, using a conventional white LED as a light source has a disadvantage that it is difficult to improve the white balance of the reproduction light. For this reason, in the illumination device of the color display liquid crystal of the present invention, the light source 10
By using three LEDs that emit light of three colors of red, green and blue instead of the white LED of the prior art, and mixing the light emitted from these three colors of LED to form white light. The white balance of the reproduction light is improved. Here, three LEDs that emit light of these three colors
Means that even if three LEDs are manufactured individually,
Needless to say, it may be formed integrally on individual substrates.

For this reason, in the lighting device of the color display liquid crystal of the present invention, the light source 10 has three colors of red, green and blue.
An LED that emits light of the three colors is used, and the light emitted from the LEDs of the three colors is mixed to form white light, and the light emitted from the LED of the light source 10 is formed as a hologram formed on the reflection surface of the light guide plate 12. Red, green and blue 3
A hologram is formed on the reflection surface of the light guide plate 12 so that light having a wavelength close to the wavelength of the color light is reflected with higher efficiency than light of other wavelengths.

By forming such a hologram on the reflection surface of the light guide plate 12, the light emitted from the red, green and blue LEDs used as the light source 10 is reflected by the hologram with high efficiency. Since light of other wavelengths hardly reflects, light projected from the hologram formed on the reflection surface of the light guide plate 12 toward the liquid crystal display panel 12 emits light from the red, green and blue LEDs of the light source 10 almost. By combining these three colors, white light with excellent white balance can be obtained.

Hereinafter, a hologram which reflects light of a specific wavelength emitted from the red, green and blue LEDs used as the light source 10 with high efficiency and which does not reflect other wavelengths as much as possible will be described. I do.

FIG. 4 is a conceptual diagram showing an optical system for forming such a hologram. As shown in the figure, as a light source for forming the hologram of the present invention, lasers 30, 31, and 32 of three colors of red, green and blue are used.
A hologram that has been multiple exposed is formed. That is, the laser light projected from the red laser 30, the green laser 31, and the blue laser 32 is converted into light on the same optical axis by the mirror 33 and the beam splitters 34 and 35, and is divided into the object light 36 and the reference light 37 by the beam splitter 35. The object light 36 is projected onto an object (in this case, a mirror) 42 via a mirror 38 and an objective lens 40, and the reflected light is projected on a photosensitive material 43 applied to a light guide plate.
The reference light 37 is projected onto the photosensitive material 43 via the mirror 39 and the objective lens 41, and the reflected light of the object light 36 and the reference light 37 interfere to form a hologram on the photosensitive material 43.

The hologram formed by superposing the lasers 30, 31, and 32 of three colors of red, green and blue and performing multiple exposure in this way produces lasers of three colors of red, green and blue. A hologram that reflects light having a wavelength close to the wavelength of the laser light projected from 31, 32 with high efficiency. Of course, the hologram actually formed as a reflection surface on the light guide plate 11 may be a hologram obtained by copying the hologram obtained in this way or a sheet obtained by attaching a sheet obtained by copying the hologram.

At this time, the red light projected from the light source 10
Since the brightness of the three colors of green and blue light varies depending on the type of the selected LED, the light diffracted as the reproduction light by the hologram formed as the reflection surface of the light guide plate 12 does not always become perfect white light. . Therefore, the output of the laser can be controlled so as to maintain a certain level of white balance, and the diffraction efficiency at the wavelength of each color can be adjusted.

Alternatively, the output of the laser when forming a hologram is formed by forming a hologram so that the diffraction efficiency is maximized at the wavelength of each color, and diffracted by the hologram formed on the reflection surface of the light guide plate 12. The white balance of the light can also be adjusted by selecting the IF current and the brightness rank of each of the LEDs that emit light of three colors, red, green and blue, which are light sources. According to this method, it is not necessary to determine the white balance by controlling the laser output when forming a hologram that is not clear what the white balance will be, and the IF current (LED) of the LED is adjusted according to the hologram of the completed light guide plate 12.
, And the rank of luminance (division of LED brightness) can be selected, so that it becomes easier to maintain the white balance at a constant level.

The hologram thus formed diffracts light having the same wavelength as that of the laser used in forming the hologram as reproduction light with the highest efficiency.
The LED used as the light source 10 includes various types of LEDs.
It is desirable to select and adopt three types of red, green, and blue LEDs that emit light having a wavelength as close as possible to the wavelength of the laser from among them. Therefore,
For example, when a hologram is formed using a helium-neon laser having a wavelength of 632.8 nm as a red laser, the peak emission wavelength is 605 nm and 612 n.
It is desirable to use a red LED of a type such as m or 615 nm as a light source. When a krypton laser having a wavelength of 647.1 nm is used, the peak emission wavelength is 660 n.
It is desirable to use a red LED of a type such as m or 700 nm as a light source.

Similarly, when a hologram is formed by using an argon laser having a wavelength of 514.5 nm as a green laser, a green LED having a peak emission wavelength of 515 nm is used as a green LED having a wavelength of 532.0 nm.
For a G laser, the peak emission wavelength is 527 nm or 53 nm.
A green LED of the type of 0 nm is desirable. When an argon laser having a wavelength of 488.0 nm is used as a blue laser, the peak emission wavelength is 472 nm.
Or a 470 nm blue LED with a wavelength of 457.
With a 9 nm argon laser, the peak emission wavelength is 42
Green LE of 8 nm, 470 nm, 472 nm, etc.
D is desirable.

This relationship can be reversed. For example, a red L of a type having a peak emission wavelength of 605 nm
When an ED is used as a light source, it is most preferable to use a helium-neon laser having a wavelength of 632.8 nm when forming a hologram. This holds true for the other LEDs as well, so that it is not necessary to consider all the LEDs here.

Further, since the peak emission wavelength of the LED also varies due to variations in the manufacturing process, etc., when higher white balance and efficiency are required, even if the same type of LED is manufactured, a large number of LEDs are manufactured. L
It is desirable to individually inspect and select the peak emission wavelengths of the group of EDs, and to use only LEDs that emit light having wavelengths closer to the respective light wavelengths of the three color lasers that have exposed the hologram. In this inspection, a sampling inspection may be performed for each lot, and when it is required to strictly adjust the wavelength, a 100% inspection may be performed.

The illumination device for a color display liquid crystal according to the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. Of course, improvements can be made.

[0029]

The lighting device for a color display liquid crystal of the present invention is
As described above, an LED that emits light of three colors, red, green, and blue, is used as a light source, and the three colors of light emitted from these LEDs are mixed to form white light, and the light is reflected on the reflection surface of the light guide plate. Forms a hologram that reflects light with wavelengths close to the wavelengths of the three colors of red, green and blue of the light source with high efficiency. The light-reflecting surface of the light guide plate, which reflects light with high efficiency and reflects only a small amount of light of other wavelengths, is obtained. The white light is a mixture of only the three colors of light of the LED, which is the light source, and is reproduced by the hologram of the light guide plate. A light source capable of maintaining a good white balance of light can provide a lighting device for a white light color display liquid crystal.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a liquid crystal display device employing a color display liquid crystal lighting device of the present invention, showing a transmission type liquid crystal display device using a backlight.

FIG. 2 is a cross-sectional view showing an example of a liquid crystal display device employing the color display liquid crystal lighting device of the present invention, which shows a transflective liquid crystal display device using a backlight.

FIG. 3 is a cross-sectional view showing an example of a liquid crystal display device employing the color display liquid crystal lighting device of the present invention, showing a reflective liquid crystal display device using a front light.

FIG. 4 is a conceptual diagram showing an optical system for forming a hologram that reflects light of a specific wavelength with high efficiency.

FIG. 5 is a schematic diagram showing a cross-sectional shape of a white LED.

FIG. 6 is a graph showing a distribution of light of a white LED for each wavelength.

[Explanation of symbols]

 Reference Signs List 10 light source 11 light guide plate 12 liquid crystal display panel 13, 14 glass substrate 15 liquid crystal 16 color filter 17 TFT surface 18, 19 polarizing plate 20 condensing sheet or diffusion sheet 21 half mirror 22 reflecting film 23 polarizing plate having compensation function 30, 31 , 32 laser 33 mirror 34, 35 beam splitter 36 object light 37 reference light 38, 39 mirror 40, 41 objective lens 42 object 43 photosensitive material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 336 G09F 9/00 337B 337 337Z H01L 33/00 M H01L 33/00 F21Y 101: 02 // F21Y 101: 02 G02F 1/1335 530 F-term (reference) 2H038 AA55 BA06 2H091 FA02Y FA14Z FA19Z FA23Z FA41X FA41Z FA45X FA45Z FC30 GA11 5F041 AA14 DC07 EE25 FF11 5G435 AA04 BB04 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB15 BB12 BB12 BB12 BB15 BB12 BB12 BB12 BB12 BB12 BB12 BB12 BB12 BB12 BB12

Claims (5)

[Claims] 1. An illuminating device for a liquid crystal display device having a light guide plate and illuminating a color display liquid crystal with light reflected by a hologram formed on a reflection surface of the light guide plate, comprising three colors of red, green and blue. A light source that uses an LED that emits light and mixes the light emitted from the three-color LEDs into white light; and a light having a wavelength similar to the wavelengths of the red, green, and blue lights of the light source. And a light guide plate formed with a hologram that reflects light with higher efficiency than light of other wavelengths. 2. A hologram that reflects light of wavelengths close to the wavelengths of red, green, and blue light of the light source with high efficiency, comprises a hologram of the light source having three wavelengths of red, green, and blue light. 2. The illumination device for a color display liquid crystal according to claim 1, wherein the hologram is a hologram that is multiple-exposed by three colors of red, green, and blue lasers having wavelengths approximate to the above. 3. An LED which emits light of three colors of red, green and blue of the light source, the light having a wavelength close to the wavelength of the light of the laser of three colors of red, green and blue exposing the hologram. Three types of LEs that emit light
3. A lighting device for a color display liquid crystal according to claim 2, wherein D is selected and adopted. 4. The LED of the light source, which emits light of three colors of red, green and blue, comprises a plurality of LEs of the predetermined type.
D is inspected, and only LEDs that emit light having a wavelength close to the wavelength of the laser light of the three colors red, green and blue that expose the hologram are individually selected and used. 4. A lighting device for a color display liquid crystal according to claim 3, wherein 5. A hologram in which light having a wavelength close to the wavelengths of the three colors of red, green and blue of the light source is reflected with higher efficiency than light of other wavelengths, the hologram having the three colors of red, green and blue The hologram is formed so as to have the maximum efficiency at each wavelength of the laser of the laser light source, and the white balance is determined based on the IF current and the luminance of each of the LEDs in the light source emitting red, green and blue light. 5. The lighting device for a color display liquid crystal according to claim 1, wherein the adjustment is performed by selecting and employing a rank.