JPH0438322Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a Fresnel structure of a transparent light guide plate used for backside identification of a transmissive display.The purpose of the invention is to use external natural light such as sunlight as a backlight for a transmissive display. An object of the present invention is to provide a Fresnel structure of a transparent light guide plate that can be used for internal light of a portable device such as a fluorescent light.

Conventional backlighting devices for transmissive displays can be roughly divided into two types. There are two methods: one uses the internal light source of the mobile device for backlighting, and the other uses external natural light such as sunlight for backlighting. The disadvantage of the former is that it requires large power consumption, which shortens the lifespan of batteries used in portable devices. Another disadvantage of the latter is that in dimly lit places, sufficient external natural light cannot be brought in. Naturally, as a solution, in order to compensate for the drawbacks of both methods, a dual-use internal light/external light type backlighting device can be considered, which can be used in combination with both systems and can be used selectively depending on the situation. This method has been available in the past, with the structure shown in FIGS. 1 and 2.

FIG. 1 shows how a conventional backlighting light guide plate of a transmissive display is used to guide light from an internal light source to the display. The back surface of the light guide plate 1 has a repeated slope structure with a constant pitch width, as shown by the Fresnel shaped portion 2, and the angle of the slope is determined by the internal light source 3.
The light source 6 emitted from the display is set so as to pass through the display 5 at the optimum clear viewing angle. FIG. 2 is a diagram showing how external natural light is incident on the light guide plate of FIG. The light can be made incident on the Fresnel shaped portion 8 of the light plate 7 and guided to the transmissive display 11 by refraction and transmission. Here, the above-mentioned internal light/external light dual use type back illumination device also has a drawback. When using external natural light, as shown in FIG. This is the point where the transmitted light of the display body 11 is tilted as it is refracted significantly. As a result, the direction of transmitted light from the display body when using internal light and when using external natural light becomes significantly different. This is illustrated by the difference in the direction of light transmitted through the display between the light source 6 for internal light in FIG. 1 and the incident light source 15 for external natural light in FIG.

Due to the above-mentioned difference in the direction of transmitted light, it is necessary to set a wide allowable range of a good clear viewing angle of the display body so that it can be used for both internal light and external natural light, which becomes a factor in increasing the cost of the display body. Also,
When a user uses a mobile device using this display, the user needs to change the clear viewing direction of the display depending on whether internal light is used or external natural light is used. This is a practical drawback. Additionally, when using external natural light, it is possible to remove the light guide plate and directly irradiate the display with natural light, which would eliminate the above-mentioned drawbacks, but it would not be possible to fix the display with the light guide plate, and a mechanism for removing the light guide plate would be required. New drawbacks arise, such as the light guide plate being easily scratched.

The present invention improves the Fresnel structure of a transparent light guide plate used for backlighting a transmissive display.
This eliminates the above-mentioned drawbacks of the conventional internal light/external natural light type back lighting device.

The details of the present invention will be explained below with reference to the drawings.
FIG. 3 is a diagram showing the light guide plate of the present invention, where 16 is the light guide plate body, and the back side of 16 is the improved Fresnel structure of the present invention. This Fresnel structure has a pitch width of 19
It has a structure in which Fresnel-shaped slope portions 17 with a pitch width of 20 and Fresnel-shaped flat portions 18 with a pitch width of 20 are alternately arranged. The ratio of pitch width 19 to pitch width 20 is approximately 2:1. Here, the above ratio is a ratio when the angle 17' of the Fresnel-shaped slope portion 17 is around 40°.

The above is the Fresnel structure of the transparent light guide plate of the present invention, and the phenomenon when external natural light is incident on the light guide plate will be explained with reference to FIG. In the conventional light guide plate, since light enters only from the Fresnel-shaped slope portion 22, all the light incident on the light guide plate is incident light ray 2.
As mentioned above, the light was refracted as shown in Fig. 4, and the clear viewing angle of the display body was tilted. In the present invention, since the Fresnel-shaped flat portion 23 is added, an incident ray 25 having a relatively small refraction angle is generated in addition to the incident ray 24. Since this incident light ray 25 is in a direction close to the normal line of the screen of the display body, it matches the clear viewing direction that is easy for the user to see. Also, since the difference in direction is small compared to the rays of internal light shown at 6 in Figure 1, the direction in which the user sees the display is almost the same whether the internal light is used or the external natural light is used. The same is fine.

Next, FIG. 5 shows how internal light is incident on the light guide plate of the present invention. The incident light ray 30 that enters the light guide plate 26 of the present invention from the internal light source 29 is reflected only at the Fresnel-shaped sloped portion, and is reflected by the Fresnel-shaped flat portion 28.
It does not hit the bottom of the valley. In short, the state of the incident light beam when using internal light is the same as that of a conventional light guide plate, and there is no drop in light guide efficiency due to the presence of the Fresnel-shaped flat portion 28.

The effects of using the backlight (for backlighting) light guide plate of the transmissive display of the present invention as described above are as follows:
It can be organized as follows.

Since the passing direction of external natural light and internal light from the display body matches the direction close to the normal line of the display screen, the clear viewing angle becomes an angle that is easy for the user to see, and the light source between external natural light and internal light is There is no need for the user to change the clear viewing angle when switching.

By configuring as described above, the following effects can be obtained.

That is, in the present invention, since the light guide plate has an inclined surface that reflects light from a light source provided on the side in the normal direction of the display screen and a flat surface that enters from the back surface of the light guide plate, a transmissive display is possible. Whether the light source of the device is internal or external, the maximum amount of light can be obtained at the optimal bright viewing angle of the display band.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a conventional backlight light guide plate for a transmissive display, Figure 2 is a diagram showing how external natural light is incident on the light guide plate of Figure 1, and Figure 3 is a diagram showing the light guide plate of the present invention. A diagram showing a light plate. FIG. 4 is a diagram showing how external natural light is incident on the light guide plate of FIG. 3. FIG. 5 is a diagram showing how internal light is incident on the light guide plate of FIG. 3. It is a diagram. In FIG. 1, 1 is a conventional light guide plate, 2 is a Fresnel-shaped portion of 1, 3 is an internal light source, 4 is a reflection plate for concentrating internal light, 5 is a transmissive display, and 6 is a ray of internal light. . In FIG. 2, 7 is a conventional light guide plate, 8 is a Fresnel-shaped portion of 7, 9 is an internal light source, 10 is a reflection plate for condensing internal light, 11 is a transmissive display, 12 is an outer box, and 13 is a A rotatable exterior door, 14 is a reflection plate, and 15 is an incident ray of external natural light. In FIG. 3, 16 is the light guide plate of the present invention, 17
is the Fresnel-shaped slope part 16, and 17' is the slope part 1.
7 angle, 18 is Fresnel shaped flat part of 16, 1
9 is a pitch width of 17, and 20 is a pitch width of 18. In FIG. 4, 21 is the light guide plate of the present invention, 22
21 is a Fresnel-shaped slope portion, 23 is a Fresnel-shaped flat surface portion of 21, and 24 is a Fresnel-shaped slope portion 22.
25 is an incident ray of external natural light that has passed through the Fresnel-shaped flat section 23. In FIG. 5, 26 is the light guide plate of the present invention, 27
26 is a Fresnel-shaped slope portion, 28 is a Fresnel-shaped flat portion of 26, 29 is an internal light source, and 30 is an incident light beam from 29.

Claims (1)

[Scope of utility model registration request] A transmissive display, and the surface facing the transmissive display moves away from the transmissive display as it moves away from the light source, and the back surface not facing the transmissive display is not parallel to the transmissive display. Formed in a rust shape,
A light guide plate that allows external natural light and light from an internal light source to enter the transmissive display, an internal light source provided on the side of the light guide plate, a reflector that allows external natural light to enter the light guide plate, and an exterior door. In the transmissive display device, a back surface of the light guide plate that does not face the transmissive display body reflects light from the internal light source in a direction normal to the screen of the transmissive display body. and a flat surface that allows external natural light incident from the back surface of the light guide plate to enter in the normal direction of the screen of the transmissive display, and is a Fresnel-shaped surface with a repeating structure of the slope and the flat surface. Transparent display device with special features.