Light source apparatus with a spherical optical member

Details Light source apparatus with a spherical optical member Light source apparatus with a spherical optical member

1998-11-13

2001-06-12

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Having a particular total or partial pressure

C313S634000, C313S635000

Reexamination Certificate

active

06246170

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting tube and a light source apparatus using the same, which are arranged to efficiently use a light flux emitted from a light emitting part and to be suited to illumination apparatuses or projection apparatuses such as a liquid crystal projector, an overhead projector and the like.
2. Description of Related Art
A light emitting tube, such as a metal-halide lamp or a high-pressure mercury lamp, has heretofore been used for the light source apparatuses such as a liquid crystal projector.
FIG. 16
schematically shows the essential parts of a light emitting tube used for a conventional liquid crystal projector. In
FIG. 16
, reference numeral
210
denotes the light emitting tube. Two arc bars
202
are disposed in the light emitting tube
210
. A middle point of a space between the two arc bars
202
is a light emission center
202
a
. The light emitting tube
210
is provided with a spherical body part
210
a
. The spherical body part
210
a
has an outer wall
210
d
and an inner wall
210
b
. The light emission center
202
a
is made to be located at a sphere center
210
c
of the outer wall
210
d
of the spherical body part
210
a.
Referring to
FIG. 16
, a light flux radiating from the light emission center
202
a
exits through the inner wall
210
b
from the spherical body part
210
a
. In this instance, the distribution angle of luminous intensity of the light flux exiting from the light emitting tube
210
is wide and has a luminous intensity distribution which is symmetrical at about 50 degrees with respect to a line perpendicular to the longitudinal direction of the light emitting tube
210
indicated by an double-headed arrow
203
, as shown in FIG.
16
.
In a case where the light emitting tube
210
having a symmetrical light intensity distribution characteristic as shown in
FIG. 16
is used in combination, for example, with an ellipsoidal mirror
211
which is employed as a light-condensing reflecting mirror, the ellipsoidal mirror
211
must be in such a shape that it has a small first focal point F
1
, as shown in
FIG. 17
, in order to use as much as possible the light emitted from the light emitting tube
210
. As a result, the ellipsoidal mirror
211
comes to have a large image-forming magnifying rate. However, in a case where an aperture provided for incidence of an illumination light is small and thus necessitates a small light source image, the large image-magnifying rate of the ellipsoidal mirror
211
makes it difficult to enhance the efficiency of illumination.
In particular, rays of light radiating at angles more than 50 degrees with respect to a line perpendicular to the longitudinal direction of the light emitting tube
210
are repeatedly total-reflected by the inner wall surface of the light emitting tube
210
to be caused to exit from the end face of the light emitting tube
210
. In other words, rays of light radiating at angles more than 50 degrees with respect to a line perpendicular to the longitudinal direction of the light emitting tube
210
fail to be projected on the reflection surface of the ellipsoidal mirror
211
and thus become wasteful light.
Further, in a case where the light emitting tube
210
having a symmetrical light intensity distribution characteristic as shown in
FIG. 16
is used in combination, for example, with a paraboloidal mirror
212
which is employed as a light-condensing reflecting mirror, the paraboloidal mirror
212
must be in such a shape that has a short focal point F, as shown in
FIG. 18
, in order to use as much as possible the light emitted from the light emitting tube
210
. Such an arrangement, however, causes rays of light reflected by the paraboloidal mirror
212
to have an inadequate degree of parallelism.
The degree of parallelism of the exiting light flux greatly degrades particularly at a part of the reflection surface of the paraboloidal mirror
212
in the neighborhood of the optical axis A, because the angle subtended by the light emission center
202
a
is large. Besides, like in the case of the ellipsoidal mirror shown in
FIG. 17
, rays of light radiating at angles more than 50 degrees with respect to a line perpendicular to the longitudinal direction of the light emitting tube
210
are repeatedly total-reflected by the inner wall surface of the light emitting tube
210
and eventually exit from the end face of the light emitting tube
210
. In other words, rays of light radiating at angles more than 50 degrees with respect to a line perpendicular to the longitudinal direction of the light emitting tube
210
fail to be projected on the reflection surface of the paraboloidal mirror
212
and thus become wasteful light.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to the solution of the problems of the prior art described in the foregoing. It is, therefore, an object of the invention to provide a light emitting tube and a light source apparatus using the same, wherein the shape of a spherical body part of the light emitting tube and the positional relation between the spherical body part and the light emission center are appositely defined to enhance the efficiency of use of a light flux emitted from the light emitting tube, in such a way as to make the light emitting tube highly suited for projectors of varied kinds.
To attain the above object, in accordance with one aspect of the invention, there is provided a light source apparatus, which comprises a spherical optical member formed with a transparent material and having an outer wall and an inner wall, and a light emitting part having a light emission center located within a space surrounded with the inner wall of the optical member, wherein the light emission center deviates from at least one of a center of the outer wall and a center of the inner wall, and the optical member is arranged to deflect in a predetermined direction a light flux emitted from the light emission center.
In accordance with another aspect of the invention, there is provided a light source apparatus, which comprises a spherical body part formed with a transparent material and having an outer wall and an inner wall, and a light emitting part having a light emission center located within a space surrounded with the inner wall of the spherical body part, wherein a light flux emitted from the light emitting part is radiated in a predetermined direction through the spherical body part, and the light source apparatus satisfies the following conditions:
D2<Rb
1.5×D3<Ra
where Ra and Rb are radii of curvature of the outer wall and the inner wall of the spherical body part, respectively, D2 is a distance from the light emission center to the inner wall, and D3 is a radius of a bar-shaped part which holds the spherical body part.


REFERENCES:
patent: 5258691 (1993-11-01), Dakin et al.
patent: 5587626 (1996-12-01), Parham et al.

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