Illumination – Plural light sources – Particular wavelength
Reexamination Certificate
2001-05-01
2003-03-25
O'Shea, Sandra (Department: 2875)
Illumination
Plural light sources
Particular wavelength
C362S035000, C362S230000, C362S246000, C362S545000, C362S558000, C362S800000
Reexamination Certificate
active
06536914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The invention relates to an illumination system having a light-emitting panel and a light mixing chamber for illuminating a display device.
2. Description of the Related Art
Such illumination systems are known per se and are alternatively referred to as edge-lighting systems. They are used, inter alia, as backlighting of (image) display devices, for example for television receivers and monitors. Such illumination systems can particularly suitably be used as a backlight for non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in (portable) computers or (cordless) telephones.
Typically, known display devices generally include a substrate provided with a regular pattern of pixels, which are each driven by at least one electrode. In order to reproduce an image or a datagraphic representation in a relevant area of a (display) screen of the (image) display device, the display device uses a control circuit. In an LCD device, the light originating from the backlight is modulated by a switch or a modulator, while applying various types of liquid crystal effects. In addition, the display may be based on electrophoretic or electromechanical effects.
In the known illumination systems, customarily a tubular low-pressure mercury-vapor discharge lamp, for example one or more compact fluorescent lamps, is used as the light source, the light which, in operation, is emitted 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 and flat panel which is made, for example, of a synthetic resin or glass, 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 optoelectronic elements, also referred to as electro-optic elements, such as electroluminescent elements, for example light-emitting diodes (LEDs). These light sources are generally provided in the proximity of or contiguous to a light-transmitting edge area of the light-emitting panel, so that, in operation, light originating from the light source is incident on the light-transmitting edge area and spreads in the panel.
U.S. Pat. No. 5,613,751 discloses an illumination system comprising a light-emitting panel and one or more light sources, which are arranged in a so-called light transition area which is coupled to or integral with the light-emitting panel, with the distribution of the light coupled out of the light-emitting panel to illuminate the display device being brought about by providing a suitable pattern of deformities in the light-emission window of the light-emitting panel.
An illumination system of the above-mentioned type has the disadvantage that the light distribution in the light-emitting panel, particularly in the proximity of the light source, is insufficiently uniform. As a result, the illumination uniformity of the display device is insufficient.
SUMMARY OF THE INVENTION
It is an object of the invention to completely or partly overcome the above-mentioned drawback. The invention more particularly aims at providing an illumination system, wherein the uniformity of the light distribution of the illumination system and hence the uniformity with which the display device is illuminated are improved.
In accordance with the invention, this object is achieved in that
the light source comprises a plurality of clusters of light-emitting diodes having different light-emission wavelengths, said clusters being arranged at a pitch P with respect to each other, and
the ratio between a height H of the light mixing chamber and the pitch P of the clusters of the light-emitting diodes meets the relation:
0.1
≦H/P
≦10,
the height H of the light mixing chamber being measured at right angles to the light-coupling edge area.
As the light-emitting diodes are clustered, mixing of the light-emitted by the light-mitting diodes (LEDs) is enhanced. An example of such a cluster is a combination of one lue LED, one green LED and one red LED. An alternative embodiment of such a cluster comprises one blue LED and one red LED in combination with two green LEDs. In addition to the above-mentioned color combinations, a cluster may comprise an amber LED.
The application of a light mixing chamber in accordance with the measure of the invention has the advantage that the light originating from the LEDs of different colors mixes well. A geometric ratio of the height of the light mixing chamber to the pitch of the clusters of LEDs in the range between said limits causes light originating from the LEDs, which is coupled into the light-emitting panel via the light-coupling edge area, to have been sufficiently mixed in the light mixing chamber when it is coupled out of the light emission window to uniformly illuminate the (image) display device.
The light mixing chamber in accordance with the invention is of simple construction and inexpensive to manufacture. This can be attributed, among other things, to the fact that it is not necessary to provide additional optical structures in the light mixing chamber to mix light originating from the LEDs of different colors. Such optical structures comprise optical elements which may, or may not, be provided with intricately curved surfaces which may, or may not, be provided with reflective coatings. Such optical elements are used to diffuse the light, emitted by the LEDs in the direction of the light-coupling edge area of the light-emitting panel, in directions along the longitudinal direction of the light mixing chamber, thereby enhancing the mixing of the light.
The lower limit of the ratio of the height of the light mixing chamber to the pitch of the clusters (H/P=0.1) is motivated by the fact that it is desirable that light beams originating from the LEDs of different colors in adjoining clusters at least touch each other at the location of the light-coupling edge area. The upper limit of the above-mentioned height/pitch ratio (H/P=10) is motivated by the fact that, in the absence of such an upper limit, (the height of) the light mixing chamber would become impracticably large and hence the edge of the (image) display device impracticably wide.
By virtue of the measure in accordance with the invention, the uniformity of the distribution of the light emitted by the illumination system is improved. As a result, a more uniform illumination of the (image) display device is obtained.
Preferably, the ratio between the height (H) of the light mixing chamber and the pitch (P) of the clusters meets the relation:
0.2
≦H/P
≦2.
The lower limit of the ratio between the height of the light mixing chamber and the pitch of the clusters (H/P=0.2) is motivated by the fact that it is desirable that light beams originating from LEDs of different colors in adjoining clusters demonstrate at least a 50% overlap at the location of the light-coupling edge area. As a result, the uniformity of the distribution of the light emitted by the illumination system is further improved. The upper limit of said height/pitch ratio (H/P=2) is dictated by the fact that, in the absence of such an upper limit, (the height of) the light mixing chamber becomes larger than the height customarily applied in (image) display devices.
The positioning of the LEDs with respect to each other in a cluster influences the way in which light issues from the light-emitting panels. A favorable embodiment of the illumination system in accordance with the invention is characterized in that the ratio between the height H of the light mixing chamber and the pitch P of the clusters of the light-emitting diodes meets the relation:
1
2
tan
β
max
≤
H
P
≤
2
tan
β
max
,
where &bgr; is the light emission angle of the light-emitting diode in a plane parallel to the longitudinal direction of the light mix
Harbers Gerard
Hoelen Christoph Gerard August
Cranson James W
Koninklijke Philips Electronics , N.V.
O'Shea Sandra
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