JPH05142537A - Illuminating device for liquid crystal - Google Patents

Abstract

PURPOSE:To make the luminance on a diffusion plate uniform by forming a reflecting plate for reflecting light from the tubular light source in a circular arc shape protruded in the rear, and placing the tubular light source in the vicinity of an extension of the circular arc of the reflecting plate. CONSTITUTION:The subject device is provided with a tubular light source 11 for illuminating a liquid crystal display plate 10 from the rear, and a reflecting plate 12 for reflecting an irradiating light to the rear fro the tubular light source 11 to the liquid crystal display plate 10 side, the tubular light source 11 is placed in the outside of an effective display area S of the liquid crystal display plate 10, and the reflecting plate 12 is curved satisfying a relation shown by an expression, wherein a distance between each reflecting point thereof and the tubular axis center of the tubular light source 11, and angle formed between a line connecting the tubular axis center of the light source 11 and each reflecting point and the vertical direction, constants are denoted as L1, theta1, and C1, C2, respectively. Therefore, light from the tubular light source 11 is limited in its directional angle by a reflecting film 13, all thereof is radiated to the reflecting plate 12, and the light is reflected forward by the reflecting plate 12, and radiated to the rear of the liquid crystal display plate 10. Accordingly illuminance of all the reflecting points on the reflecting plate 122 becomes equal, and luminance of the illumination surface in an effective display area becomes uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device used for back lighting of a light receiving type liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, illumination devices (backlight systems) for liquid crystal display devices such as laptop computers are roughly classified into a direct type and a light guide type using a light guide plate.

(1) In a direct type liquid crystal lighting device, as shown in FIG. 5, a tubular light source 2 such as a plurality of cold cathode tubes or hot cathode tubes is arranged directly below a liquid crystal display panel 1, and a tubular light source 2 is provided. A light scattering effect for uniformizing the brightness of the illumination surface between the tubular light source 2 and the liquid crystal display panel 1 across the front surface of the reflector 3 for reflecting the light emitted from the rear surface and guiding it to the front. And a diffusion plate 4 made of a milky white synthetic resin plate having

(2) The light guide type liquid crystal lighting device is shown in FIGS.
As described above, in addition to the reflection plate 3 and the diffusion plate 4 described above, polymethylmethacrylate (PMMA) excellent in light transmittance is used.
The light guide plate 5 made of acrylic resin such as
The tubular light sources 2 are arranged on both sides or one side of the display to reduce the unevenness of brightness on the entire surface and improve the display quality. In addition,
In FIG. 6, 6 is a reflector for increasing the directivity angle of the tubular light source 2 to the light guide plate, and 7 in FIG. 7 is a tubular light source reflection film for increasing the directivity angle of the tubular light source 2 to the light guide plate.

[0005]

However, in the conventional direct type liquid crystal lighting device, in order to achieve uniform brightness on the diffusion plate 4, the light emitted from the tubular light source 2 is reflected by the reflection plate 3. , PE with aluminum dot pattern
By using a writing curtain (not shown) printed on the T film, the surface brightness on the diffusion plate 4 can be made uniform to some extent. However, the streaks of the tubular light source 2 were visually confirmed on the diffuser plate 4, and the lamp unevenness inevitably occurred immediately below the tubular light source 2, leading to deterioration of display characteristics of the lighting device.

In the light guide type liquid crystal illuminator, the brightness on the diffuser plate 4 is made uniform by applying a print pattern such as white ink for light scattering to the lower and upper surfaces of the light guide plate 5. However, it has been difficult to uniformize the brightness on the diffuser plate 4 (for example, the uniformity of 90%) due to variations in the dots of the printing pattern as the brightness of the backlight becomes higher.

From the above, it has been desired to make the brightness uniform on the diffusion plate, and in particular, to make the brightness uniform by devising the shape of the reflector without taking a complicated structure.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a liquid crystal lighting device which can realize uniform brightness on the diffuser plate only by the shape of the reflector plate.

[0009]

As shown in FIGS. 1 and 2, the means for solving the problems according to the first aspect of the present invention is to provide a tubular light source 11 for illuminating the liquid crystal display panel 10 from the rear side, and a rear side from the tubular light source 11. Reflection plate 1 for reflecting irradiation light to the liquid crystal display plate 10 side
2, the tubular light source 11 is disposed outside the effective display area S of the liquid crystal display panel 10, and the reflector 12 has a distance L1 between each reflection point and the tube axis center of the tubular light source 11, and the light source 11
The tube axis center and the angle between the line and the vertical direction connecting the reflection point .theta.1, a constant as C _1, C _2, is one that is curved with a relation of the following equation.

L1 = (1 / C ₁ ) · cos (θ ₁ + C ₂ ). The means for solving the problems according to claim 2 of the present invention is to use the inner surface of the tubular light source 11 according to claim 1 so as to face the reflection plate 12. The reflection film 13 that limits the directivity angle of light is formed.

The means for solving the problem according to the third aspect of the present invention is to illuminate the liquid crystal display panel 10 from the rear side as shown in FIGS. 3 and 4, wherein the tubular light source 11 and the light from the tubular light source 11 are lit. A light guide plate 21 arranged in parallel with the liquid crystal display plate 10 so as to be guided to the light guide plate 10.
In the liquid crystal lighting device, the rear surface of the light guide plate 21 is a reflection surface 21b that reflects backward light that travels backward in the light guide plate 21. If the distance from the incident point of 21a to the reflecting point of the reflecting surface 21b is L2, the refraction angle of each irradiation ray at the light incident end face is 90 ° -θ2, and the constants are C ₁ and C ₂ , the reflection of the light guide plate 21 is described. The surface 21b is curved with the relationship of the following equation.

L2 = (1 / C ₁ ) · cos (θ ₂ + C ₂ ). The means for solving the problem according to claim 4 of the present invention is that the light incident on the light guide plate 21 is incident on the inner peripheral surface of the tubular light source 11 according to claim 3. End face 2
A reflection film 13 that limits the directivity angle of light toward 1a is formed.

[0013]

In the means for solving the problems according to claims 1 and 2, the light from the tubular light source 11 has its directivity angle limited by the reflecting film 13, and all of the light is applied to the reflecting plate 12. Then, the light is reflected forward by the reflection plate 12 and applied to the back surface of the liquid crystal display plate 10.

At this time, the illuminances of all the reflection points on the reflection plate 12 become equal, and the luminance of the illumination surface in the effective display area S becomes uniform.

In the means for solving the problems according to the third and fourth aspects, the directivity angle of the light from the tubular light source 11 is limited by the reflecting film 13, and all of the light is incident on the light incident end face 21a of the light guide plate 21.
Is irradiated. Then, the light enters the inside of the light guide plate 21 from the light incident end face 21a, is then reflected forward by the reflection face 21b, and is irradiated to the back face of the liquid crystal display plate 10.

At this time, the illuminances of all the reflection points on the reflection surface 21b become equal, and the brightness of the illumination surface in the effective display area S becomes uniform.

[0017]

【Example】

(First Embodiment) FIG. 1 is a sectional view of a liquid crystal lighting device showing a first embodiment of the present invention, and FIG. 2 is a view showing the same optical path.

As shown in the figure, the liquid crystal display device of this embodiment is
The liquid crystal display panel 10 is a direct type that does not use a light guide plate.
Of a pair of tubular light sources 11 for illuminating the light from the rear, and a reflector 1 for reflecting the light from the tubular light sources 11 to the liquid crystal display panel 10 side.
2 and.

As each of the tubular light sources 11, a straight tube type cold cathode tube or a hot cathode tube as a linear tubular light source is used. On the inner peripheral surface of the tube of the tubular light source 11, a reflecting film 13 for limiting the directivity angle of light toward the reflecting plate 12 is formed to form an aperture tube. The reflection film 13 is formed by applying the existing fluorescent material to the entire area of the inner peripheral surface of the tube, and then removing the area directed to the reflection plate 12 from the center of the tube axis. The tubular light source 11 is arranged outside the effective display area S of the liquid crystal display panel 10.

The reflection plate 12 is a metal plate having a reflectance of about 90%. The cross-sectional shape of the reflection plate 12 is curved in an arc shape protruding rearward in order to equalize the illuminance at all reflection points, and the distance between each reflection point and the tube axis center of the tubular light source 11 is L1, When the angle between each reflection point and the vertical direction of the tubular light source 11 is θ1, and arbitrary constants are C ₁ and C ₂ , the following relationship is always established.

L1 = (1 / C ₁ ) · cos (θ1 + C ₂ ) ... (1) Here, the concept of the equation (1) will be described. First, the following (a) and (b) are set as conditions for equalizing the illuminance of all the reflection points.

(A) Since the tubular light source 11 is linear, the luminous flux density is inversely proportional to the distance L from the tubular light source.

(B) Since the illuminance of the reflecting surface of the reflecting plate 12 is proportional to the brightness thereof, the surface having the same brightness when viewed from any direction (hereinafter referred to as a perfect diffusion surface) is used.

Assuming an ideal shape in which light is not attenuated in reflection on a perfect diffusing surface, the above (a),
Based on (b), the conditions for making the brightness of the perfect diffusion surface uniform are obtained. As shown in FIG. 2, with respect to the light ray G1 in the direction that is in phase with the vertical direction by θ, the distance from the tube axis center of the tubular light source 11 to the perfect diffusion surface is L, and the angle between the light ray G1 and the perfect diffusion surface is α. , Illuminance is proportional to cos α / L. Here, considering the light beam G2 that is emitted with a phase angle of a small angle dθ from the angle θ, the distance from the tube axis center of the tubular light source 11 to the perfect diffusion surface is (L + dL). Also,
The distance between the reflection point P1 on the perfect diffusion surface of the light ray G1 and the light ray G2 is L · dθ. Therefore, a differential equation such as equation (2) holds.

[0025]

[Equation 1]

When equation (2) is solved, equation (1) is obtained. This represents a circle passing through the origin with the position of the tubular light source as the origin. An example in which this solution is actually applied to a lighting device is shown in FIG. With this configuration,
The reflecting plate 13 as a perfect diffusing surface always has the same brightness regardless of the distance L from the tubular light source 11, and uniform illuminance can be obtained regardless of the inclination of the perfect diffusing reflecting surface 13. Therefore, when the liquid crystal display surface is viewed from the front side, it is possible to achieve uniform display with the same brightness as when illuminated with a planar tubular light source with uniform brightness.

(Second Embodiment) FIG. 3 is a sectional view of a liquid crystal lighting device showing a second embodiment of the present invention, and FIG. 4 is a view showing a light incident end face of a light guide plate and an optical path inside the same. ..

As shown in the figure, the liquid crystal lighting device of this embodiment illuminates the liquid crystal display panel 10 from the rear side.
The tubular light source 11 and the liquid crystal display panel 1 that emits light from the tubular light source 11
The light guide plate 2 arranged in parallel with the liquid crystal display plate 10 so as to lead to 0.
1 and 1.

As each of the tubular light sources 11, an aperture type linear tubular light source similar to that of the first embodiment is used, and the liquid crystal display panel 1 is used.
Outside the effective display area S of 0, the light incident end face 21 of the light guide plate 21
It is placed near a. On the inner peripheral surface of the tube of the tubular light source 11, there is formed a reflective film 13 that limits the directivity angle of light toward the light incident end surface 21 a of the light guide plate 21. The aperture angle φ (aperture angle) of the reflection film 13 is r, the distance between the tubular light source 11 and the light incident end face 21a of the light guide plate 12 is d, and the thickness of the light guide plate 21 is t.
Then, it becomes like the formula (3).

Φ = tan ⁻¹ {t / (r + d)} (3) The light guide plate 21 is made of a translucent acrylic resin or the like. The rear surface of the light guide plate 21 is a reflection surface 21b that reflects light traveling backward in the light guide plate 21 to the front.
The total reflection point of the reflecting surface 21b is always curved with the relationship of the expression (4).

L2 = (1 / C ₁ ) · cos (θ2 + C ₂ ) ... (4) where L2 is the distance from the incident point of the light incident end face 21a to the reflecting point of the reflecting surface 21b for each irradiation ray, C ₁ , C ₂
Indicates an arbitrary constant, and the refraction angle of each irradiation light ray at the light incident end face is 90 ° −θ2.

Here, the concept of equation (4) will be described. When the radius of the tubular light source 11 is r, the distance between the tubular light source 11 and the light incident end face 21a of the light guide plate 21 is d, and the thickness dimension of the light guide plate 21 is t, the center of the tube axis of the tubular light source 12 is taken as the origin. The shape equation of the reflecting surface 12b as the perfect diffusing surface is obtained as follows.

As shown in FIG. 4, the left tubular light source 11 was selected as the origin. The path of the light ray at an angle between the vertical direction and θi is the position where the light incident end surface 21a of the light guide plate 21 collides, that is, the light ray enters the light guide plate 21 with the tube axis center of the tubular light source 11 as the origin (0, 0). The position coordinates are (r + d,-(r + d) ・ tan (90 ° -θi)). Next, at the position coordinates where a light ray enters the light guide plate 21, the refractive index of the light guide plate 21 is n (for example, n = 1.49 in PMMA resin), and light is refracted in the light guide plate 21 according to Snell's law. Incident, then the incident angle (90 ° -θi)
The following formula is established between the refraction angles (that is, 90 ° −θ2) corresponding to

[0034]

[Equation 2]

Therefore, each θ2 (light radiated from the tubular light source lamp) corresponds to each θ2 (light traveling in the light guide) according to the equation (5). The reflecting surface 2 so that the optical path length of the light traveling through the optical plate 21 becomes L
It is sufficient to set the shape of 1b. By analogy with equation (1),

[0036]

[Equation 3]

[0037] Further, the coordinates (x, y) corresponding to each θ2 on the reflecting surface 21b are obtained by the following equation.

[0038]

[Equation 4]

When the equations (6) and (7) are arranged,

[0040]

[Equation 5]

The equation (8) is based on the coordinates (r + d,-(r + d) tan [sin ^-1 {n · sin (90 ° -θ2)}]) for each θi and θ2. It is shown that a shape in which circular arcs having a radius of / C ₁ · cos (θ ₂ + C ₂ )} are connected forms a perfect diffusion surface (21b in FIG. 4).

Even if the tubular light source 11 in the right example shown in FIG. 3 is selected as the origin, the same formula is obtained.

As described above, in both the first and second embodiments, the diffusion plate, the lighting curtain, TiO ₂ , and Ba are used.
Even without using a light scattering means such as white ink such as SO ₄ ,
The brightness of the illumination surface of the liquid crystal display plate 10 can be made uniform only by the shape of the reflection plate 12 or the reflection surface 21b of the light guide plate 21.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in the above embodiments, the tubular light source 11 is used.
However, it is also possible to adopt a configuration in which one tubular light source is received on the side edge of one side. In addition to the liquid crystal display panel, the display panel can be widely used in general, such as an electrochromic display panel and other display panels.

[0046]

According to the first and third aspects of the present invention, the illuminances of all the reflection points on the reflection surface of the reflection plate or the light guide plate become equal, and the light scattering means such as the diffusion plate or the lighting curtain is not used. Therefore, the brightness of the illumination surface can be made uniform. Therefore, the number of parts can be reduced, the processing process can be simplified, and the device is suitable for mass production.

According to claims 2 and 4, the light from the tubular light source is
If the reflector or the light guide plate can be effectively irradiated and the brightness of the illumination surface can be improved, there is an excellent effect.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal lighting device showing a first embodiment of the present invention.

FIG. 2 is a diagram similarly showing an optical path.

FIG. 3 is a cross-sectional view of a liquid crystal lighting device showing a second embodiment of the present invention.

FIG. 4 is a view showing a light incident end face of the light guide plate and an optical path inside the same.

FIG. 5 is a cross-sectional view of a conventional direct type liquid crystal lighting device.

FIG. 6 is a sectional view showing an example of a conventional light guide type liquid crystal illumination device.

FIG. 7 is a cross-sectional view showing another example of a conventional light guide type liquid crystal lighting device.

[Explanation of symbols]

 10 Liquid Crystal Display Plate 11 Tubular Light Source 12 Reflector 13 Reflective Film 21 Light Guide Plate 21a Light Incident End Face 21b Reflective Surface

Claims (4)

[Claims] 1. A tubular light source for illuminating a liquid crystal display plate from the rear, and a reflecting plate for reflecting backward light emitted from the tubular light source to the liquid crystal display plate side, the tubular light source being an effective liquid crystal display plate. The reflector is arranged outside the display area, and the distance between each reflection point and the tube axis center of the tubular light source is L1, and the angle between the line connecting the tube axis center of the light source and each reflection point and the vertical direction is θ.
1. A lighting device for a liquid crystal, wherein the lighting device for a liquid crystal has a relationship of the following equation, where C ₁ and C ₂ are constants. L1 = (1 / C ₁ ) ・ cos (θ1 + C ₂ ) 2. The inner peripheral surface of the tube of the tubular light source according to claim 1,
An illumination device for liquid crystal, comprising a reflective film formed on the reflective plate for limiting a directivity angle of light. 3. The problem solving means according to claim 3 of the present invention comprises:
A method for illuminating a liquid crystal display plate from the rear, comprising a tubular light source and a light guide plate arranged parallel to the liquid crystal display plate so as to guide light from the tubular light source to the liquid crystal display plate, the tubular light source being a light guide plate. In the liquid crystal lighting device, the rear surface of the light guide plate is a reflecting surface that reflects forward light that travels backward in the light guide plate, from the incident point of the light incident end surface for each irradiation ray. Assuming that the distance to the reflection point of the reflection surface is L2, the refraction angle at the light incident end surface of each irradiation light ray is 90 ° -θ2, and the constants are C ₁ and C ₂ , the reflection surface of the light guide plate has the following relationship. A lighting device for a liquid crystal having a curved shape. L2 = (1 / C ₁ ) ・ cos (θ2 + C ₂ ) 4. The inner peripheral surface of the tube of the tubular light source according to claim 3,
An illumination device for liquid crystal, comprising: a reflection film, which limits a directivity angle of light toward a light incident end surface of a light guide plate.