Optics: image projectors – Miscellaneous
Reexamination Certificate
1999-07-16
2001-04-24
Dowling, William (Department: 2851)
Optics: image projectors
Miscellaneous
C353S038000
Reexamination Certificate
active
06220714
ABSTRACT:
TECHNICAL FIELD
This invention relates to an image display apparatus for displaying images by modulating light from a light source by means of light valves.
BACKGROUND ART
FIG. 1
of the accompanying drawings schematically illustrate the configuration of a known projection type image display apparatus. The image display apparatus comprises a reflector plate
100
having a reflecting surface of paraboloid of revolution, a light source
101
arranged at the focal point of the reflector plate
100
, an integrator
102
, a red color separating mirror
103
R, a green color separating mirror
103
G and a blue color separating mirror
103
B.
The image display apparatus additionally comprises a cuboidal color synthesizer prism
104
so arranged as to have one of its surface
104
G be stricken by green color light reflected by the green color separating mirror
103
G, a reflector mirror
105
R so arranged as to cause red color light reflected by the red color separating mirror
103
R to strike another surface
104
R of the color synthesizer prism
104
perpendicular to the surface
104
G, another reflector mirror
105
B so arranged as to cause blue color light reflected by the blue color separating mirror
103
B to strike still another surface
104
B of the color synthesizer prism
104
parallel to the surface
104
R, an optical path length regulating lens
106
arranged between the green color separating mirror
103
G and the blue color separating mirror
103
B and another optical path length regulating lens
107
arranged between the blue color separating mirror
103
B and the reflector mirror
105
B.
The image display apparatus comprises still additionally a light valve for red light
108
R arranged between the reflector mirror
105
R and the surface
104
R of the color synthesizer prism, a lens
109
R arranged between the reflector mirror
105
R and the light valve for red light
108
R, a light valve for green light
108
G arranged between the green color separating mirror
103
G and the surface
104
G of the color synthesizer prism, another lens
109
G arranged between the green color separating mirror
103
G and the light valve for green light
108
G, a light valve for blue light
108
B arranged between the reflector mirror
105
B and the surface
104
B of the color synthesizer prism and still another lens
109
B arranged between the reflector mirror
105
B and the light valve for blue
108
B.
The image display apparatus further comprises a projector lens
110
arranged opposite to the surface of the color synthesizer prism
104
parallel to the surface
104
G.
In a projection type image display apparatus having the above described configuration, a white lamp such as a xenon lamp or a metal halide lamp is typically used for the light source
101
. Light emitted from the light source
101
is reflected by the reflector plate
100
and both ultraviolet rays and infrared rays are removed from reflected light by means of a cut filter (not shown) before reflected light is made to strike the red color separating mirror
103
R. Of the light striking the red color separating mirror
103
R, red color light is reflected by the red color separating mirror
103
R and further by the reflector mirror
105
R before it passes through the lens
109
R and the light valve for red light
108
R and enters the color synthesizer prism
104
. Light other than red Of the light striking the green color separating mirror
103
G, green color light is reflected by the green color separating mirror
103
G and then enters the color synthesizer prism
104
by way of the lens
109
G and the light valve for green
108
G. Of the light striking the green color separating mirror
103
G, light other than green color light passes through the green color separating mirror
103
G and strikes the blue color separating mirror
103
B by way of the optical path length regulating lens
106
.
Of the light striking the blue color separating mirror
103
B, blue color light is reflected by the blue color separating mirror
103
B and, after passing through the optical path length regulating lens
107
, it is further reflected by the reflector mirror
105
B and enters the color synthesizer prism
104
by way of the lens
109
B and the light valve for blue light
108
B.
All lights of different colors that enter the color synthesizer prism
104
are synthetically combined together by the color synthesizer prism
104
and passes through the projector lens
110
before projected onto a transmission type or reflection type screen.
Known projection type image display apparatus having the above described configuration is accompanied by the problem of a large spectrum width of light of each of the three primary colors separated by the respective color separating mirrors and a poor color purity. They are also accompanied by the problem of the difficulty with which the brightness of the entire quantity of light is regulated because a white lamp is used as light source and energized to show a predetermined level of brightness. Still additionally, they are accompanied by the problem of the extreme difficulty with which the brightness of each primary color is regulated because light of each primary color is separated by means of a color separating mirror.
The flux of light coming out of a white lamp normally shows a circular cross section. On the other hand, light valves to be irradiated with light normally have a rectangularly parallelepipedic profile. Therefore, the flux of light striking a light valve is required to have a diameter greater than the diagonal of the light valve in order to evenly irradiate the light valve with light. Then, there arises a problem of a poor irradiation efficiency of light emitted from the light source of any conventional image display apparatus.
As pointed out above, conventional projection type image display apparatus comprising a white lamp as light source are accompanied by a number of problems. In an attempt to avoid these problems, there has been proposed a projection type image display apparatus employing light emitting diodes of the three primary colors that are independent from each other as light source ensuring an enhanced level of color purity in order to replace the white lamp. Such a projection type image display apparatus shows an improved color reproduction ability over a wide spectral range due to the light source with high color purity such as that of light emitting diodes.
FIG. 2
shows an XY chromatogram illustrating the color reproduction spectrum of a projection type image display apparatus using light emitting diodes as light source, that of an CRT (Cathode-Ray Tube) using a fluorescent body and that of an NTSC (National Television System Committee) type image display apparatus, which are indicated respectively by symbols A
1
, A
2
and A
3
in FIG.
2
.
As seen from
FIG. 2
, while the color reproduction spectrum of a conventional projection type image display apparatus using a white lamp as light source is narrower than that of a CRT using a fluorescent body, a projection type image display apparatus using light emitting diodes as light source with high color purity can provide a color reproduction spectrum wider than that of a CRT using a fluorescent body.
However, light emitting diodes provide a surface light source and rays of light emitted from the surface light source include extra-axial rays that are located off the optical axis of the optical system comprising the light emitting diodes. Then, rays of light including extra-axial rays emitted from the light source cannot evenly and uniformly irradiate a light valve and typically show a poor light irradiation efficiency.
DISCLOSURE OF THE INVENTION
Accordingly, it is the object of the present invention to provide an image display apparatus comprising a light source with an enhanced level of color purity other than a white lamp and adapted to evenly and uniformly irradiate the light valves of the apparatus with rays of light emitted from the light source with an improved light irradiation efficiency.
According to the invention, the a
Dowling William
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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