JPS5825B2 - display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device comprising a passive electro-optic display cell and an illumination device for the display cell.

In order to observe the passive electro-optical display cell at night, it is necessary to equip it with a lighting device.

It has been established that the efficiency of such lighting devices is improved by using a powerful diffuser.

However, such a diffuser has the drawback of unintentionally reducing the daytime performance of the display cell.

However, it is an object of the present invention to overcome the above-mentioned inconvenience by providing a display device in which the light emitted from the illumination device is almost completely utilized at night without interfering with daytime observation of the display cell. It is to be.

For this purpose, the display device according to the invention comprises a diffuser, a semi-transparent mirror placed behind the display cell, and a light source, the semi-transparent mirror covering the wavelength range of the light emitted by the light source. The display is transparent at least in part, allowing the display to be read at night, and reflects light for the remainder of the visible light spectrum, making it possible to read the display during the day by its reflection. To enable this, the semi-transparent mirror reflects long wavelength bands of light corresponding to the red, yellow and green parts of the visible light spectrum, while reflecting short wavelength bands of light corresponding to the rest of the green and blue parts of the visible light spectrum. It is characterized by allowing light rays in the wavelength range to pass through.

The invention will now be described in detail with reference to the accompanying drawings, in which two embodiments of the invention are shown.

The liquid crystal passive electro-optic display cell shown in FIG.

This display cell is equipped with two polarizers 2 and 3 on the front and back sides, respectively.

A glass plate 4 serving as a light guide plate is placed behind the polarizer 3.

The front side of this glass plate is matte to serve as a diffuser and supports a semi-transparent mirror 5, such as a dielectric layer formed of a layer of dielectric material.

The glass plate 4 has a thick portion 4a on the side, and a light source 6
are arranged in said portion 4a so as to emit light of a wavelength corresponding to a short wavelength band, ie part of blue and green.

The dielectric semi-transparent mirror 5 is formed to reflect light of wavelengths corresponding to long wavelength bands, ie red, yellow and the remainder of green.

The display device described and illustrated above functions as follows.

Most of the total amount of daylight having wavelengths corresponding to red, yellow, and part of green is reflected by the semi-transparent mirror 5, and almost all of it is used for observing the display cell.

Instead, at night, the light emitted from the light source 6 passes through the semi-transparent mirror 5 and is guided toward the display cell 1, so that almost all of the light rays illuminate the display cell. The light is diffused by a matte glass plate 4 whose back surface is grooved as shown at 7 for use.

The use of long wavelength light for daytime observation and short wavelength light for nighttime observation means that the naked eye sees light with longer wavelengths than short wavelengths during the day. This is also appropriate based on the physiological evidence that humans are more sensitive to images exposed to the sun, while the opposite is true at night.

The embodiment of FIG. 2 is different from the first embodiment in that the glass plate shown at 8, which serves as a light guide plate and supports the semi-transparent mirror 5, does not have a matte surface as in the first embodiment. This example is different.

However, the role of a diffuser is ensured by a plate 9 of matte glass or any other translucent material interposed between the semitransparent mirror 5 and the polarizer 3.

Additionally, in the above two embodiments, the light guide plate can be made not only of glass but also of any transparent material.

As for general dielectric transparent mirrors, they are limited to being formed of a transparent substrate on which several vacuum-deposited dielectric layers having a more or less high refractive index are vacuum-deposited.

By choosing the materials of these different layers, as well as the thickness of the layers, what appears to be transparent at some wavelengths in the visible range is actually reflective at all wavelengths. It is possible to complete the mirror.

Such mirrors require the deposition of well over 10 layers, and the materials used are mainly ZnS and Na5AIF6PbTe.

It is also possible to complete the dielectric layer with the emission spectral function of the selected light source.

Thus, for example, if the light source is an LED light source, the dielectric layer is chosen such that its propagation band corresponds to the bright band of the LED light source, which is narrow and almost monochromatic.

The remainder of the visible light spectrum is almost entirely reflected.

For further details please refer to H. A. Macleod, “Th
n-film optical filters”
Further details can be found in Section 7.2 (published on page 156 of the same), which describes an example of a dielectric layer particularly suitable for a green light source.
b) See figure.

This mirror effectively transmits green light, but acts as a mirror at other wavelengths.

Depending on the emission spectral width of the light source, the bands of light transmitted through the mirror can be merged into this emission spectrum, but in this case not all the light energy emitted by the light source is utilized for night reading; The band transmitted through the mirror falls outside the emission spectrum.

However, this results in all the light energy being utilized without any additional installation problems.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a display device comprising a passive electro-optical display cell and a display tube illumination device, and FIG. 2 is a cross-sectional view of another embodiment. 1... Display cell, 2, 3... Polarizer,
4, 8...Glass plate, 5...Semi-transparent mirror, 6...Light source, 7...Groove, 9...Diffuser.

Claims (1)

[Scope of Claims] 1. A display device comprising a passive electrical display cell, a light source as an illumination device for the display cell, a diffuser, and a translucent mirror placed behind the display cell; The mirror reflects light in the long wavelength range corresponding to the red, yellow, and green parts of the visible light spectrum, and transmits light in the short wavelength range corresponding to the remainder of the juncture and blue. A display device characterized by: 2. The patent characterized in that the semi-transparent mirror is deposited on a plate of transparent material which serves as a light guide plate. 3. The front surface of the transparent material on which the semi-transparent mirror is deposited is matte. The display device according to claim 2, characterized in that the display device functions as a diffuser. 4. The display device according to claim 2, wherein the back surface of the mounting plate serving as a light guide plate is provided with grooves to send light emitted from the light source in the direction of the display cell. . 5. The display device according to claim 1, wherein a diffuser is interposed between the semi-transparent mirror and the display cell. 6. The display device according to claim 1, wherein the semi-transparent mirror is a dielectric mirror.