Illumination – Light modifier – Reflector
Reexamination Certificate
2001-08-09
2003-09-23
Juba, John (Department: 2872)
Illumination
Light modifier
Reflector
C362S347000, C362S350000, C313S110000, C313S323000, C313S493000
Reexamination Certificate
active
06623145
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a light source device for use in a projection-type display apparatus such as a liquid crystal projector or the like, and more particularly to an illuminating apparatus and projection-type display apparatus which employ such a light source device.
(2) Description of the Prior Art
Light source devices for use in projection-type display apparatus have a light source comprising a discharge lamp such as a xenon lamp which is of high luminance and high emission efficiency, a high-pressure mercury lamp, or a metal halide lamp, and a reflecting mirror for reflecting rays of light radiated from the light source into a parallel beam of light.
FIG. 1
of accompanying drawings is a fragmentary cross-sectional view of a conventional light source device.
As shown in
FIG. 1
, the conventional light source device comprises discharge lamp
100
having a filling material capable of maintaining discharged light emission and a pair of electrodes
102
a
,
102
b
which are sealed in tubular transparent bulb
103
of quartz or the like that is of a substantially uniform thickness, and reflecting mirror
101
having paraboloid
101
a
as a reflecting surface whose focal point is positioned at light emission center
100
a
of discharge lamp
100
. Rays of light radiated from light emission center
100
a
of discharge lamp
100
are reflected by paraboloid
101
a
of reflecting mirror
101
, and travel substantially parallel to the axis (optical axis f) of paraboloid
101
a.
The effective range in which the rays of light that are emitted from light emission center
100
a
of discharge lamp
100
can be used is defined between a ray “a” of light (inclined at angle &thgr;
1
to optical axis f) falling on paraboloid
101
a
and ray “b” of light (inclined at angle &thgr;
2
to optical axis f) falling on paraboloid
101
a.
FIG. 2
of the accompanying drawings shows a discharge lamp which is designed to increase the above effective range for an increased effective ray availability ratio (the ratio of rays of reflected light that can be used to all the rays of light emitted from the discharge lamp. The discharge lamp shown in
FIG. 2
is basically of the same structure as the discharge lamp shown in
FIG. 1
except that transparent bulb
103
has a lens structure. Specifically, transparent bulb
103
shown in
FIG. 2
has wall thickness D
1
at its center which is greater than wall thickness D
2
at a sealed end thereof, enabling transparent bulb
103
to produce a lens effect.
FIG. 2
also shows the rays “a”, “b” of light shown in
FIG. 1
which are indicated by solid lines. The lens effect of transparent bulb
103
causes rays “d”, “c” of light emitted outside of the range between the rays “a”, “b” of light in the discharge space of the transparent bulb
103
to fall on paraboloid
101
a
of reflecting mirror
101
. Therefore, the effective ray availability ratio of the light source shown in
FIG. 2
is better than the effective ray availability ratio of the light source shown in FIG.
1
.
However, since the transparent bulb having the lens effect refracts the rays of light emitted therefrom, the focal point of paraboloid
101
a
is shifted out of alignment with light emission center
100
a
, failing to produce parallel rays of light reflected from reflecting mirror
101
. Details of such a phenomenon are illustrated in
FIG. 3
of the accompanying drawings. As shown in
FIG. 3
, paraboloid
101
a
is divided into regions I, II by a boundary where ray “i” of light emitted from light emission center
100
a
and passing, unrefracted, through transparent bulb
103
is applied to paraboloid
101
a
. Region I extends from the boundary toward the closed end or crest of reflecting mirror
101
, whereas region II extends from the boundary toward the open end of reflecting mirror
101
. Ray “i” of light is reflected by paraboloid
101
a
and travels parallel to optical axis f. However, rays “h”, “g” of light reflected by region I and rays “k”, “j” of light reflected by region II do not travel parallel to optical axis f. That is, rays “h”, “g” of light reflected by region I spread at respective angles away from optical axis f, and rays “k”, “j” of light reflected by region II are intersected at respective angles toward optical axis f.
Therefore, the conventional attempt to increase the effective ray availability ratio of the light source with the lens structure of the transparent bulb has reduced the parallelism of the rays of light reflected by the reflecting mirror with the optical axis f.
Japanese laid-open patent publication No. 2000-138005 has proposed a transparent bulb that can easily be controlled in shape at the time it is fabricated, the transparent bulb having an outer wall shaped to produce parallel rays of light. However, changing the shape of the outer surface of the transparent bulb as a condensing lens poses a limitation on the correction of parallelism of the reflected rays of light.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a light source device which is of high luminance and is capable of emitting rays of light in high parallelism.
A second object of the present invention is to provide an illuminating apparatus which is of high luminance and is capable of emitting rays of light in high parallelism, using such a light source device.
A third object of the present invention is to provide a projection-type display apparatus which is of high luminance and is capable of emitting rays of light in high parallelism, using such a light source device.
To achieve the first object, a light source device according to the present invention includes a discharge lamp having a tubular transparent bulb with sealed opposite ends for generating discharged light emission near a light emission center thereof, and a reflecting mirror having a reflecting surface which comprises a curved surface approximating a paraboloid whose focal point is positioned at the light emission center of the transparent bulb, the transparent bulb having a lens structure whose wall thickness is greater at the light emission center thereof than at the sealed ends thereof, the reflecting surface being divided by a boundary where a ray of light emitted from the light emission center and passing, unrefracted, through the transparent bulb is applied to the reflecting surface, into a first curved surface extending from the boundary toward an open end of the reflecting mirror and a second curved surface extending from the boundary toward a closed end of the reflecting mirror, which is remote from the open end, the second curved surface being shaped such that the angle of incidence of a ray of light emitted from the light emission center and applied to the second curved surface is progressively smaller toward the closed end, and changes of the angle of incidence are greater than changes of the angle of incidence of a ray of light on the paraboloid.
The first curved surface may be arranged such that the angle of incidence of a ray of light emitted from the light emission center and applied to the first curved surface is progressively greater in a direction away from the boundary, and changes of the angle of incidence are greater than changes of the angle of incidence of a ray of light on the paraboloid.
To achieve the second object, an illuminating apparatus according to the present invention includes the above light source device and a condensing optical system for converging rays of light emitted from the light source device to produce uniform illuminating light.
To achieve the third object, a projection-type display apparatus according to the present invention includes the above light source device and projection image generating means for partly passing light emitted from the light source device to generate a projection image.
The present invention offers the following advantages:
The angle of incidence of a ray of light refracted by and passing through the transparent bulb, and applied to the paraboloid whose focal poi
Juba John
NEC Microwave Tube, Ltd.
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