JPH11202783A - Reflection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart an illumination structure enabling image observation in a dark environment, to a reflection type display device. SOLUTION: A light transmission plate 30 is disposed outside a panel 0 and a light source 40 is disposed at the end part of the light transmission plate 30 and generates illumination light at need. The light transmission plate 30 is disposed so as to overlap with an area inside the screen and the area outside the screen of the panel 0, and while it normally transmits external light, makes it incident on the panel 0 and emits reflected external light, it transmits the illumination light, makes it incident on the panel 0 and emits reflected illumination light at need. The light transmission plate 30 is provided with flat parts 31 divided in a belt shape and inclined parts 32 positioned between the respective flat parts, reflects the illumination light led forward from the light source 40 at the respective inclined parts 32, makes it incident on the area inside the screen of the panel 0 and emits the illumination light reflected from the area inside the screen of the panel 0 from the respective flat parts 31. The light transmission plate 30 is provided with an attenuation means 33 on the position of the area outside the screen present between the light source 40 and the area inside the screen, practically attenuates the components of a relatively large incident angle among the illumination light originated from the light source 40 in the area outside the screen and uniformly transmits the components of a relatively small incident angle to the area inside the screen in front.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type display device which performs display using external light such as natural light. More specifically, the present invention relates to a lighting structure used supplementarily when external light is scarce.

[0002]

2. Description of the Related Art A display device using a liquid crystal as an electro-optical material has a flat panel structure, and is characterized in that it is thin and lightweight and has low power consumption. The liquid crystal display device is often used for, for example, a display of a portable device by utilizing these characteristics. Unlike a self-luminous display such as an LED, a liquid crystal display (LCD) is a passive device that projects an image by transmitting and blocking external light in response to a voltage. Therefore, some illumination structure is required. Viewing from the illumination structure, the display device is classified into a transmission type and a reflection type. In the transmission type, a backlight is arranged on the back of the display device, and an image is observed from the front. The reflection type uses external light as an illumination light source as it is.

[0003]

In a transmissive display device, a panel holding a liquid crystal as an electro-optical material is formed between a pair of transparent substrates, and a light source for illumination (backlight) is arranged on the back of the panel. On the other hand, an image is observed from the front of the backlight. In the case of the transmission type, a backlight is indispensable and, for example, a cold cathode tube or the like is used. Therefore, the backlight consumes most of the power when viewed as a whole display, and is not suitable for a display of a portable device. On the other hand, in the reflection type, an external light such as natural light is incident from the front while the reflection plate is arranged on the back of the panel, and the reflected light is used to observe the image from the front. Unlike the transmissive type, which does not use a light source for backlighting, the reflective type requires relatively low power consumption and is suitable for a display of a portable device. However, the reflective display device cannot observe an image in an environment where external light is poor, such as at night, and is a problem to be solved.

[0004]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, the reflective display device according to the present invention includes a panel, a light guide plate, and a light source as a basic configuration. The panel includes a transparent first substrate located on the side of incidence of external light,
A second substrate joined to the substrate and positioned on the reflection side, an electro-optical material held in the gap, and an electrode formed on at least one of the first and second substrates and applying a voltage to the electro-optical material; I have. The light guide plate is made of a transparent material, is disposed outside the first substrate, and overlaps the in-screen area and the off-screen area of the panel. A light source is disposed at an end of the light guide plate and generates illumination light as needed. As a characteristic feature, the light guide plate usually transmits external light and enters the first substrate and the second light guide plate.
While the external light reflected from the substrate is emitted, the illumination light is guided as needed to be incident on the first substrate and the illumination light reflected from the second substrate is emitted. The light guide plate has a flat portion divided into a strip shape and an inclined portion located between the flat portions, and the illumination light guided forward from the light source is reflected at each inclined portion to form the panel. And the illumination light reflected from the in-screen region of the panel is emitted from each flat portion. As a further feature, the light guide plate has an attenuating unit at a position of an off-screen region between the light source and the in-screen region, and a component having a relatively large incident angle in illumination light emitted from the light source. Is substantially attenuated in the region outside the screen, and the component having a relatively small incident angle is guided toward the front region inside the screen. Preferably, the attenuation means is a light diffusion layer formed on a surface of the light guide plate. Alternatively, the attenuation means may be a light absorbing layer formed on a surface of the light guide plate.

[0005] The structure of the light guide plate described above is also applicable to a light guide plate incorporated in a backlight used in a transmissive display device. That is, the transmissive display device according to the present invention includes a panel, a light guide plate, and a light source as a basic configuration.
The panel is a transparent first substrate located on the front side, a transparent second substrate joined to the first substrate via a predetermined gap and located on the back side, an electro-optical material held in the gap, and An electrode is formed on at least one of the first substrate and the second substrate, and applies an voltage to the electro-optical material. The light guide plate is disposed outside the second substrate and overlaps the in-screen area and the off-screen area of the panel. A light source is provided at an end of the light guide plate to generate illumination light. As a characteristic feature, the light guide plate has band-shaped inclined portions arranged at predetermined intervals, and reflects the illumination light guided forward from the light source at each inclined portion to the panel from the back side. Incident on the screen. The light guide plate has an attenuating unit at a position in an off-screen region between the light source and the in-screen region. The attenuating means substantially attenuates a component having a relatively large incident angle of the illumination light emitted from the light source in the region outside the screen, and guides a component having a relatively small incident angle toward the front region within the screen. .

According to the present invention, the light guide plate is arranged on the surface of the reflection type panel, and the light source is arranged at the end. In a dark environment, the light source is turned on, and illumination light is incident on the panel side via the light guide plate to display an image. In a bright environment, the light source is turned off, and an image is projected using external light directly through a transparent light guide plate. The light guide plate is basically transparent and does not hinder the observation of an image even in a bright environment. As described above, according to the present invention, the light source only needs to be turned on when necessary, and the power consumption of the entire display can be significantly reduced, which is suitable for a display of a portable device. In addition to the basic functions described above, the present invention devises to enhance the image quality especially in a dark environment. That is, the light guide plate has an attenuating means at a position of an off-screen area between the light source and the in-screen area of the panel,
By substantially attenuating the component having a relatively large incident angle in the region outside the screen in the illumination light emitted from the light source, and guiding the component having a relatively small incident angle toward the front in-screen region,
It enables uniform nighttime illumination without unevenness.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view showing a conceptual configuration of a reflective display device according to the present invention. As shown in the figure, the reflective display device includes a panel 0, a light guide plate 30, and a light source 40 as a basic configuration. Panel 0
Is a transparent first substrate 1 located on the incident side of external light, a second substrate 2 joined to the first substrate 1 via a predetermined gap and located on the reflection side, and held in a gap between the two substrates 1 and 2. Electro-optic material 3
And an electrode formed on at least one of the first substrate 1 and the second substrate 2 for applying a voltage to the electro-optical material 3. The light guide plate 30 is made of, for example, an injection-molded product of a transparent material such as an acrylic resin, and is arranged outside the first substrate 1. Light source 40
Are provided at the end of the light guide plate 30 and generate illumination light as needed. The light source 40 is formed of, for example, a cold cathode tube, and is called a so-called edge light. In order to improve the illumination efficiency of the edge light, a reflecting mirror 41 is provided behind the cylindrical light source 40.
Is arranged. In such a configuration, the light guide plate 30 normally transmits the external light, enters the first substrate 1 and emits the external light reflected from the second substrate 2, and guides the illumination light as needed to make the first light. The illumination light that has entered the substrate 1 and reflected from the second substrate 2 is emitted. Although not shown, a reflection layer is provided on the second substrate 2 side.

The light guide plate 30 has a flat portion 31 divided into strips.
And an inclined portion 32 located between the flat portions 31. The illumination light guided forward from the light source 40 is reflected by the inclined portions 32 and is incident on the in-screen area of the panel 0. The illumination light reflected from the in-screen region of the panel is emitted from each flat portion 31. As a characteristic feature, the light guide plate 30 has an attenuation unit 33 at a position outside the screen between the light source 40 and the area inside the screen. The attenuating means 33 is composed of, for example, a light diffusion layer or a light absorbing layer, and substantially attenuates a component having a relatively large incident angle in the off-screen region of the illumination light emitted from the light source 40, and reduces a component having a relatively small incident angle. The light is guided toward the front in-screen area. With such a configuration, it becomes possible to uniformly illuminate panel 0 over the entire area within the screen.

FIG. 2 is a schematic diagram for explaining the function of the light guide plate 30. In addition, the light guide plate not provided with the attenuation means is shown. Illumination light PH with a large incident angle emitted from the light source
The oblique light indicated by the dotted line is guided forward while being reflected by the flat portion 31 of the light guide plate 30. On the other hand, the illumination light PL (parallel light indicated by the solid line) having a small incident angle is totally reflected by the 45 ° inclined portion 32 and emitted in a direction perpendicular to the light guide plate 30. This vertically emitted illumination light PL is used for illumination of the reflective liquid crystal panel.

FIG. 3 shows a state in which the light guide plate shown in FIG. As mentioned earlier,
Panel 0 is generally divided into an in-screen area constituting an effective screen and an out-of-screen area around the area. Peripheral circuits and the like are formed in the area outside the screen, and a mirror reflection layer 9a is generally provided. On the other hand, the scattering reflection layer 9 is arranged in the area within the screen. Illumination light PL with a small incident angle emitted from the light source
Proceeds in the same manner as the simple substance shown in FIG. However,
The reflection angle of the illumination light PH having a large incident angle is changed by the scattering / reflection layer 9 in the in-screen area of the panel 0, so that the light cannot travel forward in the light guide plate 30 as in a single body. It is emitted toward. Therefore, the illuminance of panel 0 is bright on the light source side and dark on the front side.

FIG. 4 shows a state in which a light guide plate 30 provided with an attenuating means in a region outside the screen according to the present invention is used for a panel 0. In this example, a light diffusion layer 33a is provided as an attenuation means. Instead, a light absorbing layer may be used. The illumination light PH having a large incident angle emitted from the light source first enters the flat portion 31 in a region outside the screen. As described above, the light diffusion layer 33a is formed in a band shape on the flat portion 31 as an attenuation means. Here, the illumination light PH is diffused, and the angle with respect to the horizontal direction of the light guide plate 30 is sharply increased, and consequently is confined in an off-screen region. When a light absorption layer is provided instead of the light diffusion layer 33a, the illumination light PH with a large incident angle emitted from the light source is absorbed here, and is not guided toward the in-screen region. Therefore, the light guided to the in-screen region beyond the out-of-screen region is the illumination light P having a small incident angle.
L, whereby the area within the screen can be uniformly illuminated.

When a light guide plate having no attenuating means is used, as the width of the flat portion 31 increases, the difference in luminance between the light source side and the front side increases. For example, the width of the 45 ° inclined portion 32 was fixed at 6 μm, and the flat portion 31 having the width of 70 μm and 252 μm was prototyped. With the light guide plate in which the width of the flat portion 31 was 70 μm, uniform illumination could be achieved over the entire in-screen area without providing any attenuating means. However, the width dimension of the flat portion 31 is 25
With the light guide plate having a thickness of 2 μm, the luminance on the light source side was double that of the front side. When the light guide plate having the flat portion 31 with the width dimension of 252 μm was provided with an attenuating means composed of a light diffusion layer having a width of 5 mm, illumination without luminance difference could be performed over the entire area within the screen.

FIG. 5 is a schematic partial sectional view showing an embodiment of the reflection type display device according to the present invention. This embodiment basically has a flat structure in which the light guide plate 130 and the panel are overlapped. The light guide plate 130 is provided with an attenuating means (not shown) in addition to the flat portion 131 and the inclined portion 132. The panel has an active matrix configuration. The upper substrate 101 is located on the incident side in contact with the light guide plate 130 and is made of a transparent base material such as glass. On the other hand, the lower substrate 102 is located on the reflection side, and it is not always necessary to use a transparent material. A guest host liquid crystal layer 103 is held in a gap between the pair of substrates 101 and 102. The guest-host liquid crystal layer 103 is mainly composed of a nematic liquid crystal 104 having a negative dielectric anisotropy, and contains a dichroic dye 105 at a predetermined ratio. However, the present invention is not limited to the guest-host liquid crystal, and liquid crystals of other display modes can be used. On the surface of the upper substrate 101, a counter electrode 106 and an alignment film 107 are formed. Further, a color filter 150 is also formed. Alignment film 1
Reference numeral 07 is made of, for example, a polyimide film, and vertically aligns the guest-host liquid crystal layer 103. Lower substrate 102
At least, a switching element composed of a thin film transistor 108, a scattering reflection layer 109, and a pixel electrode 111 are formed. The scattering reflection layer 109 is flattened by the flattening layer 114, and the pixel electrode 111 is patterned thereon. Therefore, the pixel electrode 111 and the counter electrode 106
And a sufficient electric field can be applied to the guest-host liquid crystal layer 103. The pixel electrode 111 has a flattening layer 11
4, and is electrically connected to the thin film transistor 108 via a contact hole 112 opened.

As described above, the flattening layer 11 for filling the unevenness of the scattering reflection layer 109 and the thin film transistor 108.
4, the pixel electrode 111 is connected to the thin film transistor 108 via the contact hole 112. The scattering reflection layer 109 is subdivided corresponding to each pixel electrode 111. Each of the subdivided portions is connected to the same potential as the corresponding pixel electrode 111. The scattering reflection layer 109 is used for preventing specular reflection of incident light and improving image quality. An alignment film 115 is formed so as to cover the surface of the pixel electrode 111, and is in contact with the guest-host liquid crystal layer 103 to control the alignment. In the present embodiment, this alignment film 115 is
Together with the above, the guest host liquid crystal layer 103 is vertically aligned.

The thin film transistor 108 has a bottom gate structure, and has a laminated structure in which a gate electrode 116, a gate insulating film 117, and a semiconductor thin film 118 are sequentially stacked from the bottom. The semiconductor thin film 118 is made of, for example, polycrystalline silicon, and a channel region aligned with the gate electrode 116 is protected from above by a stopper 119. The bottom-gate thin film transistor 108 having such a configuration is covered with the interlayer insulating film 120. Interlayer insulating film 12
0 has a pair of contact holes, through which the source electrode 121 and the drain electrode 122 are electrically connected to the thin film transistor 108. These electrodes 121 and 122 are, for example, patterned aluminum. The drain electrode 122 is formed on the scattering reflection layer 10.
9 and the same potential. The pixel electrode 111 is connected to the drain electrode 1 through the contact hole 112 described above.
22 is electrically connected. On the other hand, a signal voltage is supplied to the source electrode 121.

FIG. 6 is a schematic plan view of the active matrix type display device shown in FIG. As shown, the display device 200 includes a pixel array unit 204 included in an in-screen area 203, a peripheral circuit included in an out-of-screen area, and a plurality of input terminals 20 that supply signals from the outside.
5 is included.

The pixel array section 204 has pixels arranged in rows and columns. Each pixel includes a pixel electrode PXL and a switching thin film transistor Tr. Further, it has gate lines X arranged in rows and signal lines Y arranged in columns. The gate electrode of each thin film transistor Tr is connected to the corresponding gate line X, the source electrode is connected to the corresponding signal line Y, and the drain electrode is connected to the corresponding pixel electrode PXL.

The peripheral circuit section has vertical driving means for selectively driving each row of pixels in accordance with a signal supplied from the input terminal 205, and horizontal driving means for selectively driving selected pixels in column order. I have. In this example, the vertical driving means is composed of a pair of vertical driving circuits 206 and 207 arranged on both left and right sides of the in-screen area 203, and selects and drives each row of pixels simultaneously from both sides. While the first vertical driving circuit 206 is connected to the left end of the gate line X, the second vertical driving circuit 20
7 is connected to the right end side of the gate line X. The vertical drive circuits 206 and 207 sequentially output gate pulses at the same timing, and open / close the thin film transistor Tr for each row to perform the above-described pixel selective drive. On the other hand, the horizontal driving means is composed of a single horizontal driving circuit 208 and is connected to one end of the signal line Y. The horizontal drive circuit 208 distributes a video signal supplied from the outside via the input terminal 5 to each signal line Y, and writes and drives selected pixels in column order. The vertical drive circuits 206 and 207 and the horizontal drive circuit 208 described above are arranged in the area outside the screen, while the pixel array unit 204 is arranged in the area 20 inside the screen.
3

FIG. 7 shows a state in which a light guide plate and a light source are set in the reflection type display device shown in FIG. As shown, a light source 240 is provided at an end of the reflective display device 200. The display device 200 has a central in-screen area 20.
3 and a surrounding off-screen area 213. As described above, peripheral circuits are integrated and formed in the off-screen area 213, and basically have a specular reflection structure. On the other hand, in the in-screen region 203, pixel electrodes and thin film transistors for switching and driving these are integrally formed.
Basically, it has a scattering reflection structure. Although the light guide plate is not shown, a light guide plate having no attenuating means is used for convenience of explanation.

FIG. 8 is a schematic graph showing the brightness distribution of the screen of the display device shown in FIG. The horizontal axis indicates the vertical position of the screen, and the vertical axis indicates brightness. On the graph,
x0 corresponds to the end of the off-screen area 213 shown in FIG.
x1 corresponds to the boundary between the in-screen area 203 and the out-of-screen area 213. As is clear from the graph of FIG. 8, if no attenuating means is provided on the light guide plate, an extremely bright area Z is generated at the end of the in-screen area 203 close to the light source 240. This significantly impairs the appearance of the in-screen area 203. The phenomenon shown in FIG. 8 corresponds to the state schematically shown in FIG. As shown in FIG.
A large amount of illumination light is emitted to the outside in a portion of the in-screen region close to the out-of-screen region, so that only this portion becomes particularly bright. Therefore, as shown in FIG. 4, by providing, for example, a light diffusion layer as an attenuating means in the off-screen area, unnecessary illumination light that may leak into the screen is confined in the off-screen area.

The structure of the light guide plate according to the present invention can be applied not only to the above-mentioned reflective display device but also to a backlight of a transmissive display device. This application example is shown in FIG. As shown, the present transmissive display device includes a panel 300, a light guide plate 330, and a light source 340 as a basic configuration.
The panel 300 is a transparent first substrate 30 located on the front side.
1. A transparent second substrate 302 bonded to the first substrate 301 via a predetermined gap and located on the back side, an electro-optical material held in the gap, and the first substrate 301 and the second substrate At least one of the electrodes 302 has an electrode for applying a voltage to the electro-optical material. In this example, the electro-optical material is T
A pair of polarizing plates 370 and 380 is disposed on both sides of the panel 300 in this relation. The light guide plate 330 is disposed outside the second substrate 302 and overlaps the in-screen area and the off-screen area of the panel 300. The light diffusion plate 360 is interposed between the light guide plate 330 and the panel 300. The light source 340 is provided at an end of the light guide plate 330 and generates illumination light. The light source 340 is the reflecting mirror 3
41. The light guide plate 330 has band-shaped inclined portions 332 arranged at a predetermined interval, and reflects the illumination light guided forward from the light source 340 at each inclined portion 332 so that the screen of the panel 300 is viewed from the rear side. It is incident on the inner area.
A light reflecting plate 390 is provided to assist the incidence of the illumination light. As a feature, the light guide plate 330 is
Attenuating means 333 is provided at a position outside the screen between 0 and the area inside the screen, and a component having a relatively large incident angle of the illumination light emitted from the light source 340 is substantially attenuated in the outside screen area. Then, a component having a relatively small incident angle is guided toward a front in-screen area. Thereby, it is possible to uniformly illuminate the area in the screen of the transmission type display device from the back. The attenuating means 333 is composed of, for example, a light diffusion layer formed on at least one surface of the light guide plate 330. Alternatively, the attenuation means 333 may be a light absorbing layer formed on at least one surface of the light guide plate 330.

[0022]

As described above, according to the present invention,
A light guide plate is provided on a reflective panel, and a light source for auxiliary illumination is provided at an end of the light guide plate. The light guide plate normally transmits external light to enter the panel and emits external light reflected from the panel, and, if necessary, guides illumination light to enter the panel and emits illumination light reflected from the panel as necessary. . In a dark environment, the light source is turned on so that an image can be observed even with a reflective panel. On the other hand, in a bright environment with abundant external light, the light source is turned off to save power. The light guide plate has flat portions divided into strips and inclined portions located between the flat portions, and the illumination light guided forward from the light source is reflected by each of the inclined portions to be reflected on the screen of the panel. The illumination light that enters the region and is reflected from the in-screen region of the panel is emitted from each flat portion. The light guide plate has attenuating means at a position of an off-screen region between the light source and the in-screen region, and a component having a relatively large incident angle of the illumination light emitted from the light source is substantially generated in the off-screen region. By attenuating and guiding the component having a relatively small angle of incidence toward the front in-screen region, uniform illumination of the in-screen region is realized. By using the light guide plate having such a configuration for backlighting of the transmissive display device, it is possible to achieve uniform backlighting in a region within the screen.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic concept of a reflective display device according to the present invention.

FIG. 2 is a schematic view showing a reference example of a light guide plate.

FIG. 3 is a reference example showing a use state of the light guide plate.

FIG. 4 is a schematic diagram illustrating a use state and a function of the light guide plate according to the present invention.

FIG. 5 is a schematic partial cross-sectional view showing an embodiment of the reflective display device according to the present invention.

FIG. 6 is a schematic plan view of a reflective display device.

FIG. 7 is a schematic plan view showing a reference example in which a light guide plate and a light source are incorporated in the reflective display device shown in FIG.

8 is a graph showing a brightness distribution of a screen of the display device shown in FIG.

FIG. 9 is a cross-sectional view illustrating an embodiment of a transmissive display device according to the present invention.

[Explanation of symbols]

0 ... panel, 1 ... first substrate, 2 ... second substrate, 3 ... electro-optical material, 30 ... light guide plate, 31 ...
..Flat portions, 32 ... inclined portions, 33 ... damping means,
40 ... light source

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02F 1/1335 520 G02F 1/1335 520 530 530

Claims (6)

[Claims] 1. A transparent first substrate located on an incident side of external light, a second substrate joined to the first substrate via a predetermined gap and located on a reflection side, and electro-optic held in the gap. material,
And a panel formed on at least one of the first substrate and the second substrate and provided with an electrode for applying a voltage to the electro-optical material; and an in-screen area and a screen of the panel disposed outside the first substrate A light guide plate overlapping the outer region; and a light source disposed at an end of the light guide plate and generating illumination light as needed. The light guide plate normally transmits external light and enters the first substrate. And emits external light reflected from the second substrate, and guides illumination light as required to enter the first substrate and emit the external light.
A reflection type display device that emits illumination light reflected from a substrate, wherein the light guide plate has a flat portion divided into a strip shape and an inclined portion located between the flat portions, and is directed forward from the light source. The illumination light guided toward each panel is reflected by each inclined portion to enter the in-screen region of the panel, and the illumination light reflected from the in-screen region of the panel is emitted from each flat portion, and the light guide plate is Attenuating means is provided at a position of the off-screen region between the light source and the in-screen region, and a component having a relatively large incident angle of illumination light emitted from the light source is substantially reduced in the off-screen region. A reflection-type display device, wherein a component that is attenuated and has a relatively small incident angle is guided toward a front in-screen region. 2. The reflection type display device according to claim 1, wherein said attenuation means is a light diffusion layer formed on a surface of said light guide plate. 3. The reflection type display device according to claim 1, wherein said attenuation means is a light absorbing layer formed on a surface of said light guide plate. 4. A transparent first substrate located on the front side, a transparent second substrate joined to the first substrate via a predetermined gap and located on the back side, and an electro-optical material held in the gap. And a panel formed on at least one of the first substrate and the second substrate and provided with an electrode for applying a voltage to the electro-optic material; and a screen area and a screen of the panel disposed outside the second substrate. A light guide plate overlapping the outer region, and a light source arranged at an end of the light guide plate to generate illumination light, wherein the light guide plate has a band-shaped inclined portion arranged at a predetermined interval; The illumination light guided forward from the light source is reflected by each inclined portion and is incident on the in-screen area of the panel from the back side, and the light guide plate is located between the light source and the in-screen area. An attenuating means is provided at the position of the off-screen area, and the illumination light emitted from the light source has a relatively large incident angle. A transmissive display device, wherein the light is substantially attenuated in the area outside the screen, and a component having a relatively small incident angle is guided toward the area inside the screen in front. 5. The transmission type display device according to claim 4, wherein said attenuating means is a light diffusion layer formed on at least one surface of said light guide plate. 6. The transmission type display device according to claim 4, wherein said attenuating means is a light absorbing layer formed on at least one surface of said light guide plate.