Illumination – Revolving
Reexamination Certificate
2001-10-25
2004-01-06
Tso, Laura K. (Department: 2875)
Illumination
Revolving
C362S293000
Reexamination Certificate
active
06672734
ABSTRACT:
BACKGROUND
1. Field of Invention
The invention relates to an illumination system for illuminating a display device, which illumination system is provided with a light-emitting panel comprising
a front wall and, opposite thereto, a rear wall as well as a first and a second light-transmitting edge surface which are situated between the front wall and the rear wall,
at least one first light source being associated with the first edge surface and at least one second light source being associated with the second edge surface, and
in operation, light originating from the first light source being incident on the first light-transmitting edge surface, and light originating from the second light source being incident on the second light-transmitting edge surface, said light spreading in the light-emitting panel.
The invention also relates to a display device provided with said illumination system.
2. Description of Related Art
Such illumination systems are known per se and are also referred to as edge lighting systems. They are applied, inter alia, as backlighting of (image) display devices, for example for television receivers and monitors. Such illumination systems can particularly suitably be used as backlights for non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are employed in (portable) computers or (cordless) telephones.
Such display devices generally comprise a substrate provided with a regular pattern of picture elements (pixels), which are each controlled by at least one electrode. In order to form an image or a datagraphic display in a relevant area of a (display) screen of the (image) display device, the display device employs a control circuit. In a LCD device, the light originating from the backlight is modulated by means of a switch or a modulator, whereby various types of liquid crystal effects are employed. In addition, the display may be based on electrophoretic or electromechanical effects.
In the illumination systems mentioned in the opening paragraph, a tubular low-pressure mercury-vapor discharge lamp, for example one or more compact fluorescent lamps, is generally used as the light source, the light emitted, in operation, by the light source being coupled into the light-emitting panel which serves as an optical waveguide. This optical waveguide generally forms a comparatively thin, flat panel which is made of, for example, a synthetic resin or glass, with light being transported through the optical waveguide under the influence of (total) internal reflection.
Such an illumination system may also be provided with an alternative light source in the form of a plurality of opto-electronic elements, also referred to as electro-optic elements, such as electroluminescent elements, in particular light-emitting diodes (LEDs). These light sources are generally provided so as to be close to or abut against a light-transmitting edge surface of the light-emitting panel, so that, in operation, light originating from the light source is incident on the light-transmitting edge surface and spreads into the panel.
In U.S. Pat. No. 5,664,862, a description is given of an illumination system for illuminating a LCD panel. For the light source use is made of incandescent lamps. Other light sources, such as fluorescent lamps and light-emitting diodes are also mentioned. In operation, the light source couples light into the light-emitting panel via a first light-transmitting edge surface, said light-emitting panel also being referred to as light guide. The rear wall of the light-emitting panel is provided with coupling-out members, also referred to as facets. These facets are preferably shaped such that light entering the panel via the first light-transmitting edge surface is reflected, predominantly in the longitudinal direction of the panel, in the direction of the opposite second light-transmitting edge surface. The light reflected at this second light-transmitting edge surface strikes the facets, as a result of which the light is partly deflected so as to be coupled out of the light-emitting panel, and partly continues on its way through the light-emitting panel. The facets are provided in the rear wall in such a manner that a uniform light distribution on the LCD panel to be illuminated is obtained.
An illumination system of the above-mentioned type has the disadvantage that the light distribution in the light-emitting panel, particularly close to the light source, is insufficiently uniform. As a result, the display device is illuminated insufficiently uniformly.
SUMMARY
It is an object of the invention to completely or partly obviate said drawbacks. The invention more particularly aims at providing an illumination system of the type mentioned in the opening paragraph, wherein the uniformity of the light distribution of the illumination system, and hence the uniformity with which the display device is illuminated, is improved.
In accordance with the invention, this object is achieved in that,
a first sub-surface of the front wall or of the rear wall of the light-emitting panel is provided with first coupling-out members for coupling light out of the panel, which light predominantly originates from the first light source, and
in that a second sub-surface of the front wall or of the rear wall of the light-emitting panel is provided with second coupling-out members for coupling light out of the panel, which light predominantly originates from the second light source,
the concentration of the first coupling-out members near the second edge surface being higher than the concentration of the second coupling-out members, and
the concentration of the second coupling-out members near the first edge surface being higher than the concentration of the first coupling-out members.
By dividing the coupling-out members into first coupling-out members, which predominantly couple out light originating from the first light source, and second coupling-out members, which predominantly couple out light originating from the second light source, and by clustering these coupling-out members into, respectively, a first sub-surface and a second sub-surface, said sub-surfaces being positioned at some distance from the edge surface where the light of the relevant first or second light source is coupled into the light-emitting panel, it becomes possible to use a part of the light-emitting panel to mix light originating from the respective light sources before the light of these light sources contacts coupling-out members which couple light out of the light-emitting panel. By raising the concentration of the first coupling-out members close to the second edge surface, which first coupling-out members have a preference for coupling-out light originating (directly) from the first light source, it is achieved that light originating from the first light source first travels through the light-emitting panel for a while, as a result of which the risk of the light striking coupling-out members coupling out said light is comparatively small. In other words, if the concentration of the second coupling-out members near the first edge surface is chosen to be higher than the concentration of the first coupling-out members, a substantial part of the light originating (directly) from the first light source is coupled out of the light-emitting panel at locations which are situated at a comparatively large distance from the first edge surface. The same is true for light originating from the second light source. By raising the concentration of the second coupling-out members close to the first edge surface, which second coupling-out members have a preference for coupling out light originating (directly) from the second light source, it is achieved that light originating from the second light source first travels through the light-emitting panel for a while, as a result of which the risk of the light striking coupling-out members coupling out said light is comparatively small.
Using a part of the light-emitting panel to enhance the mixing of light has the additional advantage t
Lumileds Lighting U.S. LLC
Patent Law Group LLP
Tso Laura K.
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