1. Field of the Invention
The present invention relates to a display device.
2. Description of the Related Art
CRTs are widely used as display devices. A CRT has a great depth because it has a single electron gun assembly which applies an electron beam to all pixels provided. Further, it is heavy and consumes much electric power. It is therefore not suitable for a portable display device. Other kinds of display devices, such as plasma displays, EL displays and the like, are available but can hardly be used as portable display devices for various reasons.
Only one portable display device put to practical use is a liquid crystal display. Thin and driven at a low voltage, the liquid crystal display is used in large numbers in wrist watches, pocket calculators and the like. In particular, TN-type liquid crystal displays have become incorporated in TV sets since they incorporate active switching elements (e.g., TFTs) and can exhibit display characteristics comparable with those of CRTs. However, TN-type liquid crystal displays uses light at low efficiency since they have a polarizing plates. They need to have a back light for supplementing light and inevitably consume much electric power.
A liquid crystal display which has no polarizing plate are known. It is known as "polymer-dispersed type displays," which utilize scattered light. The polymer-dispersed type display cannot display multi-color images, as does a reflective direct-view type display. Each RGB pixel used in this display can utilize but only those components of transmitting light which fall within only a third of wavelength region, in order to display a color dot as in a light-transmitting type display. Comprised of three light-transmitting regions (red, green and blue regions), each RGB pixel can use only a ninth of the light passing through it for displaying a color dot. The amount of light used in, for example, a red region is so small that the light emitted from the red region, is a very dark red, appearing almost black.
Furthermore, if a magenta filter, a cyan filter and a yellow filter are provided, respectively covering the three color regions of each RGB pixel, the polymer-dispersed type display can display neither high-luminance color images nor high-contrast monochrome images. This problem, which is inherent in any light-scattering, direct-view display (including a polymer dispersed type display), has yet to be solved. In other words, none of the light-scattering, direct-view type display hitherto known can be practically used as color display.