Illumination – Revolving
Reexamination Certificate
2000-03-13
2002-03-26
Sember, Thomas M. (Department: 2875)
Illumination
Revolving
C362S551000, C362S554000
Reexamination Certificate
active
06361180
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates generally to light diffusing apparatus or flat light devices, which are widely used for general lighting or illumination, and for backlight illuminating passive type display devices such as liquid crystal display devices. More particularly, the invention relates to light diffusing apparatus or flat light devices utilizing an edge lighting effect in which light rays are repeatedly reflected between front and rear surfaces of a light transmission panel.
Furthermore, the invention generally relates to passive type display devices with light diffusing apparatus or flat light source devices for use in backlight illuminating passive type display devices and more particularly to passive type display devices having surface light source or flat light source devices utilizing the edge lighting effect.
(2) Description of Related Art
Liquid crystal displays are a typical example of passive type displays, which do not emit light by their selves, and this differs from active type displays, which emit light by their selves such as CRTs and electro luminescent devices. Accordingly, liquid crystal displays of the transmissible type, as opposed to the reflective type, are utilized in combination with a flat light source or light transmission panel for backlighting which is located in the rear of such displays, so that the display can be clearly viewed by a user in dark environments as well as bright environments.
Conventionally, such light transmission panels are widely used for the flat light sources as backlights or film viewers to illuminate the passive type displays such as liquid crystal displays of transmissible type or transparency films with visual information such as photographic transparency films or OHP (overhead projector) transparency films, by combination with light sources such as linear fluorescent lamps, located at side surface of the light transmission panel (i.e. positioned laterally the light transmission panel.)
This type of lighting system is called an “edge lighting”, or “light transmission panel” system, and the light transmission panel is made of transparent material with high light transmission characteristics such as acrylic resin and polycarbonate resin and glass. Light rays emitted from at least a light source are input to at least a side i.e. lateral surface of the light transmission panel. Such light rays are repeatedly reflected between front and rear surfaces in the light transmission panel. The light rays leak or are output gradually according to transmission of light rays to illuminate an object such as a liquid crystal display or a photographic transparency film.
The light transmission panel is ordinarily a panel or film having a rectangular surface area to be illuminated, which substantially corresponds to that of the liquid crystal display.
The light transmission panel for illumination has rectangular surfaces with two long sides and two short sides. There are following four types of the arrangement according to the positional relationships between the light transmission panel and the linear light source such as a linear fluorescent lamp:
(1) An arrangement in the short side-single light type in which a single linear light source is placed at a short side surface of the light transmission panel;
(2) An arrangement in the long side-single light type in which a single linear light source is placed at a long side surface of the light transmission panel;
(3) An arrangement in the short side-dual light type in which a linear light source is placed at each of the two short side surfaces of the light transmission panel; and
(4) An arrangement in the long side-dual lights type in which a linear light source is placed at each of the two long side surfaces of the light transmission panel.
As is well known in the field, light rays incident on the light transmission panel for illumination are transmitted inside the light transmission panel, and the light rays repeat internal total reflections from the light incident side to opposite side in the light transmission panel. Some quantity of transmitted light reaches the opposite side in the light transmission panel. The rest of the transmitted light leaks progressively from the surface of the light transmission panel for illumination to the outside of the light transmission panel to illuminate a passive type display or a photographic transparency film.
Accordingly, in the case in which the short side-single light type or long side-single light type is used, the brightness of a surface projecting from the surface of the light transmission panel is falls off rapidly according to the distance from the light source. Such single light types cannot produce uniform surface brightness and have lower surface brightness according to the distance from the light source. In the case in which a light transmission panel with a large surface area must be illuminated, the single light types cannot be used because the distance over which light is to be transmitted is too great and the brightness of the surface is extremely low near the opposite side terminal which is far from the light input side in the light transmission panel.
Therefore, the single light types are limited to use in color liquid crystal displays of small surface area or to use in monochrome displays not requiring relatively high and uniform surface brightness. The dual light types are used in color and monochrome liquid crystal displays with large surface areas requiring relatively high and uniform surface brightness, such as monitors or displays for personal computers or television receivers. In particular, portable electronic devices, driven by battery power sources and having liquid crystal displays with backlights, must be light in weight and compact, such as in notebook or palm-sized personal computers and information and telecommunication terminals. The dual light types using fluorescent lamps are not suitable for this purpose because the weight is almost double and space in the housing for accommodating the lamps is almost double compared to the single light type.
Fluorescent lamps have variable brightness and the emission at different locations on the lamp surface because, for example, blacking increases from the electrodes toward the center of the lamp over time, as is known in fluorescent lamps for general lighting purposes. Furthermore, the area blackened is increases over time and the area blackened differs from lamp to lamp. Therefore, in dual light types using fluorescent lamps, uniformity in brightness and color displayed at different points on the surface of the light transmission panel decreases over time compared to the single light type.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel light diffusing apparatus including light guide means.
Another object of the present invention is to provide a novel light diffusing apparatus including light guide means capable of outputting light with a desired distribution of luminance or brightness.
Still another object of the present invention is to provide a novel light diffusing apparatus including light guide means capable of outputting light with substantially uniform distribution of luminance or brightness.
The light diffusing apparatus of the present invention can be suitably used in various optical devices such as surface light devices, light indicators, backlights or front lights of passive displays e.g. liquid crystal displays (LCDs) and vehicle lights.
The present invention includes a first light guide portion for light leakage i.e. light diffusion, a second light guide portion solely for light transmission and a third light guide portion for an optical communication with the first light guide portion and said second light guide portion. The first, second and third light guide portions may form substantially a single piece construction.
The first light guide portion may be comprised of a first side surface (i.e. a first end or a first end face) and the second light guide portion is further comprise
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