LCD projector

Details LCD projector LCD projector

2000-10-26

2002-06-25

Dowling, William (Department: 2851)

Optics: image projectors

Lamp control

C353S094000

Reexamination Certificate

active

06409350

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a liquid crystal display (LCD) projector in which an output of a light source is set selectively.
BACKGROUND ART
An LCD projector is known from, for example, Japanese Patent Laid-Open Publication No. 5-313115 (1993).
FIG. 14
shows a basic construction of this known LCD projector. In
FIG. 14
, a main power source
210
supplies electric power to an on-off switch
220
for turning on and off a light source
230
. The known LCD projector further includes a condensing lens
240
, an LCD panel
250
acting as an image forming member, a projecting lens system
260
and a screen
270
.
A halogen lamp or the like is used as the light source
230
. A light ray from the light source
230
not only is condensed but is converted into collimated rays by the condensing lens
240
. The collimated rays are supplied from the condensing lens
240
to the LCD panel
250
in which an image is formed. Subsequently, the image of the LCD panel
250
is projected onto the screen
270
through enlargement by the projecting lens system
260
such that an enlarged image is formed on the screen
270
.
As the voltage is applied across the thickness direction of the LCD panel
250
, the rate of transparency T varies in an S curve as shown in FIG.
15
.
Generally, in an LCD projector, it is often desirable to change luminance of a light source in accordance with its user's preference or brightness of a room in which the LCD projector is installed. For example, if luminance of the light source is reduced in accordance with the factors referred to above, service life of the light source can be lengthened as compared with a case in which the light source is driven at its maximum luminance at all times.
However, in the known LCD projector of
FIG. 14
, it is impossible to change luminance of the light source
230
. Namely, in this known LCD projector, since the light source
230
is driven at its maximum luminance at all times, luminance of the light source
230
gradually drops merely upon lapse of integrated on-state period of the light source
230
as shown in FIG.
16
. Therefore, the known LCD projector has such disadvantages that service life of the light source
230
is short and electric power consumed by the known LCD projector is large.
DISCLOSURE OF INVENTION
Accordingly, an object of the present invention is to provide an LCD projector in which service life of a light source is lengthened and electric power consumed by the LCD projector is saved.
In order to accomplish this object of the present invention, an LCD projector according to the present invention comprises: a power source; an image data source for producing an image data; a light source which is able to provide different levels of power; an LCD panel for modifying a light ray from the light source in accordance with said image data to produce light rays of an image; a projecting lens for projecting the light rays from the LCD panel onto a screen through enlargement; a control circuit for controlling an output of the power source so as to selectively set an output power: and a correcting circuit for correcting an image data before being supplied to the LCD panel so as to compensate the disturbance of the white balance caused by the change of the power of the light source.
The correcting circuit further corrects said image data so as to compensate the light intensity change caused by the intrinsic transparency characteristics of the LCD panel.
In accordance with the present invention, since luminance of the light source is changed in accordance with a user's preference or brightness of a room in which the LCD projector is installed, service life of the light source can be lengthened and electric power consumed by the LCD projector can be saved.


REFERENCES:
patent: 3914645 (1975-10-01), Li Donnici
patent: 4964719 (1990-10-01), Tachikawa et al.
patent: 5504544 (1996-04-01), Dreyer et al.
patent: 5567030 (1996-10-01), Shin
patent: 5658062 (1997-08-01), Lee et al.
patent: RE36060 (1999-01-01), Miyashita
patent: 196 21 911 (1997-12-01), None
patent: 0 801 507 (1997-10-01), None
patent: 0 888 016 (1998-12-01), None
patent: 1-213694 (1989-08-01), None
patent: 3-282418 (1991-12-01), None
patent: 5-313115 (1993-11-01), None
patent: 6-60833 (1994-08-01), None
patent: 7-56545 (1995-03-01), None
patent: 9-288272 (1997-11-01), None
patent: 95/20811 (1995-08-01), None

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