JP2002008422A - Liquid crystal lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate that enhances efficiency in usage of light by increasing ratio of an upward vertical component of light which illuminates liquid crystal and increasing amount of light incident in eyes of a viewer to a liquid crystal display by means of using comparatively simple parts, and reducing shade generation by using prism rows (Fresnel). SOLUTION: It is characterized that plural reflecting planes made of a transparent dielectric substance are arranged laterally at a fixed angle respectively and display is carried out by illuminating liquid crystal with light irradiated from the surface of light guide substance of a plate-like arranged shape.

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 a backlight or the like of a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a surface illuminating device used for such an application, as shown in FIG. 3, a substantially parallel light beam radiated from a rod-shaped light source and reflected by a parabolic reflector is used as an end of a light guide plate. The light further enters the light guide plate, passes through one surface of a large number of triangular prisms formed on the lower surface of the light guide plate, reflects downward from the surface of the adjacent prism, and irradiates a diffusion sheet provided below the light guide plate. Referring to FIG. 3, the light beam (L) incident on the light guide plate (50) is reflected downward on the surface (50s) of the prism, irradiates the diffuser plate (51), and is diffused by the diffuser plate (L). Are (L1), (L2), (L
3). . . A part of the reflected diffused light that is diffused and reflected as described above is transmitted through the light guide plate to illuminate the liquid crystal display panel (30) installed above.

Alternatively, as shown in FIG. 4, light incident on the light guide plate is reflected obliquely upward by one surface of a plurality of prisms formed on the lower surface of the light guide plate to reflect the light obliquely upward. The reflected light is transmitted through the light guide plate at a certain exit angle and emitted upward, and the emitted light is emitted vertically upward by the prism sheet installed on the upper part of the light guide plate. Referring to FIG. 4, the light (L) incident on the light guide plate (60) is reflected upward by the inner surface (60s) of the micro prism formed below the light guide plate, passes through the light guide plate, and passes through the prism sheet (61). The incident prism sheet is formed of a large number of triangular prisms. Light obliquely incident on the prism sheet is reflected vertically upward on one inner surface (61s) of the triangular prism to illuminate the liquid crystal display panel. is there. Usually, a combination of a diffusion plate method and a prism sheet method is often used.

[0004]

However, in the conventional diffusion method, the light incident on the end face of the light guide plate once passes through the surface of the light guide plate and irradiates the diffusion plate provided under the light guide plate.
Indirect illumination using a diffuser as a secondary light source provides a wide viewing angle, but a light source with a small upward vertical component and poor light use efficiency.

[0005] In both the diffusion type and the prism sheet type, in the conventional illuminating device, the light incident on the light guide plate transmits or reflects the light downward through a plurality of prisms formed on the lower surface of the light guide plate, or reflects the light upward. It is necessary to reflect the light directly on the prism, and the shadow of the prism array (Fresnel) is inevitable (Fig. 3
In FIG. 4, 51A, 51B, and 51C are displayed, and in FIG.
00A, 600B. . . , 610A, 610B. . . ,
Is inevitable on the lower surface of the light guide plate and the prism sheet surface, and the area where uneven illumination occurs is increased.

The apex and the valley of the prism have a shape close to a semicircle having a certain size in terms of processing accuracy, and light incident on the prism is diffused at the apex and the valley to reduce the light use efficiency. The finer the prism, the greater the light diffusion rate.

In the prism sheet system, a prism sheet is indispensable, and the number of parts increases.

The upper surface of the light guide plate also needs a prism array for aligning the exit angles of light rays. This prism is also required in the present invention, and the conditions for generating a shadow are the same as those of a conventional light guide. . Therefore, in FIGS. 3 and 4, the display is omitted to avoid complication of the drawings, and the description of the problem is omitted.

[0009]

It is desired that a liquid crystal lighting device has a wide and thin structure. Therefore, a thin light source and a thin light guide plate are used, and most of the light is used for illuminating the liquid crystal. It is necessary to increase the efficiency of use of the garbage. This means that illumination unevenness is reduced by a light beam having a large upper vertical component and a large area is irradiated. In other words, the light traveling direction is 90
Minimize the number of prisms and micro-reflection surfaces to bend as much as possible (reduce shadows and reduce uneven illumination)
This means that light is specularly reflected (minimizing loss for bending the traveling direction of light) on a surface close to continuity. To reduce illumination unevenness, avoid the discrete arrangement of light reflection and transmission surfaces (Fresnel shape, which often generates shadows) when arranging a large number of prisms, and use only a few relatively long reflection surfaces. It is desired that the reflective surface be arranged and be substantially continuous with the reflective surface. Further, it is also desired that the luminous flux illuminating the liquid crystal has an appropriate spread, and that the illuminating system has a field of view that is not inconvenient for a viewer of the liquid crystal.

Accordingly, an object of the present invention is to provide a surface illumination device having high light use efficiency. In order to achieve this object, the illuminating device of the present invention uses a prism reflecting mirror made of a plurality of transparent dielectrics to reduce a light beam having a small thickness incident from the lateral direction in a wide range (a sheet-shaped light beam) in an upward direction. Is to reflect and radiate.

The light reflectance and transmittance on the prism surface made of a transparent dielectric are determined by the refractive index of the dielectric and the incident angle (reflection angle).
Is a function of If the refractive index of the dielectric is fixed, the reflectance can be freely controlled by changing the incident angle. However, the reflected light is partially polarized. Usually, a liquid crystal display device arranges polarizing plates above and below liquid crystal, and displays a pattern using polarized light. In general, light incident on a dielectric surface is a P component whose vibration plane of an electric vector oscillates in a plane parallel to the plane of incidence (a plane including the direction of light incidence and the normal to the plane of incidence), and a P component perpendicular to this plane. And the S component oscillating on the surface. In this manual, the surface on which light is incident on a prism or the like is referred to as an incident surface, and is distinguished from the incident surface. The light reflected from the reflecting surface of the dielectric prism is a generally partially polarized light beam having a large S component and a small P component. Originally, the liquid crystal uses a polarized light beam to create the shading of the screen. If the illumination of the liquid crystal is light polarized to the S component, as described in the example of the present invention,
There is no problem with an illumination optical system using only light polarized in the component.

In the illumination device of the present invention, a plurality of quadrangular prisms are installed, and the amount of the S component radiated upward from each quadrangular prism (hereinafter, expressed only as the amount of light) is set to be equal. The purpose is to emit a uniform amount of light over the entire surface of the light guide plate. A light beam bundle having a small thickness emitted from a light source unit composed of a rod-shaped light source similar to a linear light source and a parabolic reflector is first formed by a reflecting surface of a first quadrangular prism and an incident surface of a second quadrangular prism. Then, the light is reflected upward and radiated with the reflectance and the reflection angle at which a predetermined light amount is obtained. Light rays refracted and transmitted by the reflection surface of the first quadrilateral prism enter the second quadrilateral prism. The reflection surface of the second quadrangular prism is set at an angle of incidence (reflection) at which the amount of light reflected and radiated by the first quadrangular prism becomes the same as the amount of light radiated, and reflects light upward. The third and subsequent quadrangular prisms are also set to the reflecting surface and the incident surface are set to the incident (reflective) angle at which the same amount of light as the first is emitted, similarly to the second prism. When the remaining light amount transmitted through the plurality of quadrilateral prisms becomes equal to the amount of reflection and radiation of each prism pair, the last reflector is a reflecting mirror that performs total reflection. It is desirable to form a large number of prism rows on the upper surface of the quadrilateral prism so as to make the light beam perpendicular to the incident surface of the liquid crystal. Thus, the present invention
By providing a plurality of dielectric prisms that reflect and transmit light, a thin liquid crystal lighting device can be provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, (21) is a lamp such as a cold cathode discharge tube.
(22) is a parabolic reflector having the discharge tube as a focal point, and serves as a light source for emitting light to the light guide plate by the discharge tube and the reflector. Most of the light emitted from the discharge tube (21) is reflected by the reflecting mirror (22), and is a light beam nearly parallel in cross section. In each of the quadrangular prism rows constituting the light guide plate (10), the reflecting surface (S12) of the first prism (1) and the incident surface (S21) of the second prism (2) are arranged in parallel. Similarly, the prisms 2, 3, 3, 4, 4, 5, 5, and 6, and the reflecting surface and the incident surface are arranged so as to be parallel to each other to form a light guide plate. As described above, the reflectance of light on the dielectric surface is equal to that of P which vibrates parallel to the incident surface.
The wave differs from the S wave oscillating perpendicularly to it, ie the reflected light beam is partially polarized. Either polarized light may be used to illuminate the liquid crystal. In the text, an S wave will be described as an example.

The situation of light transmission and reflection will be described in detail with reference to FIGS. In FIG. 1, a light beam emitted from the light source unit is incident on a first quadrangular prism (1) constituting a light guide plate (10). In FIG. 2, the incident light beam (L) travels straight in parallel to the upper and lower surfaces of the light guide plate, and is reflected (L1) on the reflecting surface (S12) which is a smooth slope of the prism on the opposite surface of the incident surface (S11). On the other hand, the light ray (L2) refracted and transmitted without being reflected on the surface (S12) is refracted and incident on the incident surface (S21) of the second prism (2), and is incident on the prism (2) as a light ray (L3). On the other hand, part of the light beam (L4) reflected on the incident surface (S21) of the second prism (2) is again
The light is refracted and transmitted through the reflection surface (S12) of the first prism (1), travels to the upper left as a light ray (L5) in parallel with the first reflected light (L1), and furthermore, the reflection surface (S12) of the prism (1).
A part of the light ray (L6) reflected to the right of the second prism (2) passes through the incident surface (S21) of the second prism (2), and the incident light ray (L6)
7). Similarly, the light ray is repeatedly reflected and transmitted between the slits of the prisms (1) and (2), and becomes light traveling upward and left in the first prism (1) and light transmitted to the second prism (2). That is, the light beam traveling to the upper left in the first prism (1) is the light beam reflected by the reflection surface (S12),
It is the sum total of the light beams transmitted through the reflection surface (S12) to the upper left among the light beams repeatedly reflected and transmitted between the slits of the first and second prisms. The remaining light enters the second prism (2).

The prisms (2), (3), (4),
In (5), in the same manner as in the first prism, the incoming light beam is split into a light beam that travels in the upper left direction in the prism and a light beam that enters the next prism. Is reflected, so that the angle of the reflection surface (S62) is set to an incident / reflection angle equal to or larger than the total reflection critical angle. Of course, the reflection surface (S62) may be replaced with a metal reflection surface that totally reflects.

At this time, the angles (K1), (K2)... Of the reflecting surfaces of the prisms are set so that the total sum (total light amount) of light traveling upward in each prism is equal. . . (K6) is set.

On the upper surface of the quadrilateral prism constituting the light guide plate, when light is emitted from the upper surface, a large number of light beams are transmitted in order to reduce the loss of light transmission due to reflection on the surface, and further refract the light to emit vertically upward. Micro prism array ((F1) (F
2). . . ) Is formed. Quadrilateral prism (1)
Reflected on the reflecting surface (S12) of the second or next prism (2)
Are reflected by the entrance surface (21), re-transmitted to the reflection surface (S12), and travel in the upper left direction, are refracted by the micro prism array ((F1) (F2). Radiated in the direction. Micro prism arrays are similarly formed on the upper surfaces of the other quadrangular prisms.

The light emitted above the light guide plate is supplied to a polarizer (31) and an analyzer (32) placed on the light guide plate.
The liquid crystal display plate (30) sandwiched by the polarizing plates is transmitted and illuminated to display a liquid crystal.

As described above, according to the present invention, unlike a conventional light guide plate, a method in which a fine prism is formed on a light guide plate or a prism sheet and the use efficiency of light utilizing reflection and diffusion is low is considered. Differently, a quadrangular prism having a relatively large reflecting surface (1) (2). . . By arranging a small number of
The polarized light necessary for illuminating the liquid crystal can be efficiently emitted vertically upward without forming a large number of fine prism rows for bending the light, and a wide range of surface light source can be easily formed.

However, to view the liquid crystal display panel, an appropriate viewing angle is required, and for that purpose, it is necessary to appropriately widen the light emission angle. Fortunately, the luminous flux emitted from the light source unit consisting of a parabolic mirror and a discharge tube cannot be perfectly parallel light because the discharge tube has a certain size, and becomes a light beam with an appropriate spread. Inevitably, the luminous flux emitted upward from the quadrilateral prism becomes a luminous flux having an appropriate spread,
It can be illuminated with a light beam having an appropriate spread. Alternatively, by slightly changing the angle of the incident surface with respect to the reflecting surface between adjacent prisms arranged in parallel, the light beam re-entering the reflecting surface of the preceding prism is inclined, and the emission angle of light emitted upward Can be changed, this is to make the light beam spread. Of course, the spread of the light beam can be freely changed by changing the shape of the reflector of the discharge tube.

For reference, the invention has been described below.
The design values of the reflected light and the reflection angle of the reflection surface in a system in which the light guide plate is composed of six quadrangular prisms are described in a table. The design condition is 1. The emitted light is a design value for an S wave that vibrates perpendicularly to the incident surface. 2. The material of the prism has no birefringence and has a refractive index of 1.5 for both P and S waves. (Note) Reflectance: The reflectance at which light rays parallel to the upper and lower surfaces of the light guide plate are reflected by the reflecting surface. Reflection surface reflection light amount: The light amount reflected on the reflection surface when the light amount incident on the first prism (1) of the light guide plate is 1. Re-incident light amount: When the amount of light incident on the first prism (1) of the light guide plate is 1, the amount of light that is reflected on the incident surface, re-enters the reflecting surface, and is emitted upward.

Referring to FIG. 5, another embodiment using a flat plate as a light reflecting surface will be described. In the example described above, the reflecting surface (S12) and the incident surface (S21) of the prism have been described as examples of the surface that reflects light upward. Otherwise, as equivalent to the above-described embodiment, instead of the quadrilateral prism,
A flat plate-shaped space surrounded by the reflecting surfaces ((S12), (S22)...) And the incident surface ((S21), (S31). Is to replace it.

In this case, in order to make the amount of light reflected upward the same value as that of the above-mentioned prism type, the incident angle (reflection angle) becomes almost twice as large as that of the prism type, and the reflected light beam is considerably inclined. It becomes a ray. In order to direct the tilted light vertically upward, a triangular prism array ((P1) (P2)) is formed below the transmission plate (40) formed above the reflection plate ((41) (42) ...). The light incident on the prism is reflected by the other surface of the prism and emitted vertically upward.

The behavior of the light beam is described above as shown in FIG.

This is the same as the prism type of the present invention. The light (L10) emitted from the light source unit partially reflects on the upper surface of the reflecting plate (41) to the right upper surface, enters the prism (P3) as a light beam (L11), is reflected by the other surface of the prism, and is reflected upward. Is radiated. The light (L100) will be described as an example.
The remaining light is incident on the reflection plate (41). The incident light is repeatedly reflected and emitted in the reflection plate (41),
Light ray group (L101) emitted to the upper surface of the reflection flat plate (41)
And a light ray group (L102) transmitting through the lower surface. The ray group (L101) emitted to the upper surface enters the prism and is emitted to the upper surface similarly to the reflected light beam (L11), and the ray group (L102) transmitted through the lower surface enters the upper surface of the next reflecting flat plate (43). . As described above, the reflection flat plates (41, 42, 4)
3. . . ) Light is repeatedly reflected and transmitted on the upper and lower surfaces to reflect light upward. The light ray (L
15) is reflected by a total reflection mirror (45) made of metal or the like and emitted upward.

[0025]

The present invention has the following effects. (B) The number of reflecting surfaces that bends horizontal light beams into upward vertical light beams is several, and the reflected light is close to a continuous reflecting surface, thus reducing shadows. (B) Since the number of reflecting surfaces is small, the amount of light that is diffused at the vertices and valleys of the prism and becomes unnecessary decreases, and the light use efficiency increases. (C) The light guide plate can be composed of one component, and there is no need to use another component such as a prism sheet.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a lighting device according to an embodiment of the present invention.

FIG. 2 is a detailed view of a light beam passing through a first prism (1) in the present invention.

FIG. 3 is a cross-sectional view of a conventional lighting device that illuminates a diffusion plate and uses the diffusion plate as a secondary light source.

FIG. 4 is a cross-sectional view of a conventional lighting device using a prism sheet.

FIG. 5 is a sectional view of another embodiment in which the reflection surface is replaced by a transparent flat plate.

Claims (2)

[Claims] 1. A liquid crystal lighting device having a flat plate shape which reflects light emitted from a light source and incident on an end face to an upper surface and emits the reflected light, the light incident on an incident surface of a quadrangular prism made of a transparent dielectric material. The light that was partially reflected on the exit surface of the prism and transmitted through the remaining exit surface was partially reflected on the incident surface of the next prism adjacent to that surface, and the rest was incident on the adjacent prism. Prism pairs, multiple 1
Arranged in rows, the sum of the amount of light reflected on the exit surface of the previous prism and the amount of light reflected on the entrance surface of the next prism and re-entering the exit surface of the previous prism is, for each adjacent prism surface pair,
A liquid crystal lighting device in which a plurality of prisms each having a quadrangular cross section defining the inclination angle between the exit surface and the entrance surface of each prism surface pair are arranged in substantially the same manner. 2. A flat-panel liquid crystal lighting device which radiates a light beam emitted from a light source and incident on an end face to an upper surface and emits the reflected light. A liquid crystal lighting device in which plane plates are arranged and arranged at an angle such that the sum of light reflected on the front and back surfaces of each plane plate and emitted upward is substantially the same.