Illumination – Light source and modifier – Plural serial lens elements or components
Reexamination Certificate
1998-03-04
2001-11-06
O'Shea, Sandra (Department: 2871)
Illumination
Light source and modifier
Plural serial lens elements or components
C362S308000, C362S331000
Reexamination Certificate
active
06312143
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an illumination device, more particularly an illumination device for a projection or display apparatus and especially an illumination device of an optical valve such as a liquid-crystal screen.
DESCRIPTION OF THE PRIOR ART
A projection apparatus essentially comprises an illumination device making it possible to project at least one image such as that produced by means of an optical valve, more particularly by means of a liquid-crystal screen. In this case, the image generated is projected onto a screen by a projection optic. In the case of a display device, the image is displayed directly on the liquid-crystal screen. A known illumination device used for this type of apparatus includes, as shown in
FIG. 1
, a lamp
1
, which may be an arc lamp, a halogen lamp, a neon lamp or a filament lamp, and a reflector
2
, preferably a parabolic reflector, in order to reflect the light and focus the light rays onto a surface such as a liquid-crystal screen
3
. This type of illumination device has a number of drawbacks. This is because the shape of the beam reflected by the parabolic reflector is different from that of the optical valve onto which it is directed. However, an optical valve requires a uniform and a strong illumination. With a parabolic reflector, there may therefore be considerable light losses which may be at least 45% for the illumination of a valve of rectangular shape, especially a valve of the 16/9 type. Moreover, when the optical valve is a liquid-crystal screen, this must be provided with a polarizer and with a polarization analyser since the source is unpolarized. This leads to an additional loss which may be as much as 60 to 70%. Consequently, with an illumination device of this type and as shown in
FIG. 2
, a low illumination uniformity and a light efficiency of approximately 30% are observed. The average illumination aperture is approximately ±5° and the solid angle is not optimized. This means that the light distribution is not uniform within the solid angle.
SUMMARY OF THE INVENTION
The object of the present invention is to remedy these drawbacks by providing a novel illumination device making it possible to obtain an illumination shape which corresponds to the format of the surface to be illuminated and gives a high illumination uniformity.
The subject of the present invention is a device for illuminating at least one surface, which includes a light source and a reflector in order to focus the light rays emitted by the source, characterized in that the focal plane of the reflector lies between the light source and the said surface and in that it includes, positioned close to the focal plane of the reflector, a means forming a second light source.
According to one particular embodiment, the reflector has an ellipsoidal shape and the surface receiving the illumination consists of an optical valve such as a liquid-crystal screen, the optical valve being associated, preferably on the entrance side, with a field lens which collimates the beam emanating from the second light source.
According to a first embodiment, the means forming a second light source consists of a microlens array optionally followed by a thick lens.
According to a second embodiment, the means forming a second light source consists of a diffuser optionally followed by a thick lens.
Other features and advantages of the present invention will appear on reading the detailed description of several embodiments, this description being given with reference to the drawings appended hereto, in which:
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Drazic Valter
Marcellin-Dibon Eric
Sarayeddine Khaled
Kolodka Joseph J.
Laks Joseph J.
Neils Peggy A
O'Shea Sandra
Thomson Multimedia S.A.
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