Electric lamp and discharge devices – With temperature modifier – Having heat conducting path
Reexamination Certificate
2001-03-15
2003-12-23
Hodges, Matt (Department: 2879)
Electric lamp and discharge devices
With temperature modifier
Having heat conducting path
C313S045000, C313S040000, C313S026000, C313S013000, C349S161000
Reexamination Certificate
active
06667567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a light source unit, and more particularly to a light source unit which is capable of preventing temperature increase therein.
2. Description of the Related Art
As a liquid crystal display device has been fabricated in a larger size, a liquid crystal display device is required to have a higher brightness and a wider view angle.
In order to accomplish a higher brightness in a liquid crystal display device, transmissivity of a liquid crystal panel and an efficiency at which a light is used have been improved. However, there is a limitation in such ways, and hence, a brightness in a light source unit is presently tried to increase.
A wider view angle in a liquid crystal display device is often accompanied with a demerit that a transmissivity of a liquid crystal panel is deteriorated. In order to compensate for such a demerit, a brightness in a light source unit is required to increase.
That is, a higher brightness in a light source unit would accomplish a higher brightness and a wider view angle in a liquid crystal display device.
However, it would be necessary to supply an increased power to a light source unit in order to accomplish a higher brightness in a light source unit. It is well known that about 10 to 40% of an energy emitted from a light source unit is lost as heat radiation. That is, as an increasing power is supplied to a light source, heat generated in the light source increases, and heat loss also increases.
If a light source increasingly generates heat, a liquid crystal panel positioned in the vicinity of the light source would be heated accordingly, resulting in that display quality in the liquid crystal panel would be degraded because the liquid crystal panel has a display characteristic which is influenced by heat.
Thus, there has been a demand for a liquid crystal display device which is capable of accomplishing a higher brightness without degradation in display quality.
As a solution to the above-mentioned problem, a shield in which a liquid crystal display device is housed has been equipped with a fun or a heat sink.
Hereinbelow is explained conventional light source units used in a liquid crystal display device.
FIG. 1A
is a perspective view of a conventional liquid crystal display device, and
FIG. 1B
is a cross-sectional view taken along the line
1
B—
1
B in FIG.
1
A.
The illustrated liquid crystal display device
1
is comprised of a liquid crystal panel
2
, a shield
3
in which the liquid crystal panel
2
and a light source unit
4
(see
FIG. 1B
) are accommodated, a heat radiator
7
formed on a rear surface of the shield
3
, and parts
8
mounted on a rear surface of the shield
3
.
A shield front
31
a
defining a front surface of the shield
31
is formed with an opening
31
a
through which a part of the liquid crystal panel
2
is exposed. A exposed portion of the liquid crystal panel
2
defines a display screen of the liquid crystal display device
1
.
As illustrated in
FIG. 1B
, the heat radiator
7
is mounted on a shield rear
33
defining a rear surface of the shield
3
. The shield rear
33
is composed of metal having high thermal conductivity and being light, such as aluminum.
Heat generated in the light source unit
4
is radiated through the shield rear
33
having high heat radiation property.
As illustrated in
FIG. 1B
, the liquid crystal display device
1
includes the liquid crystal panel
2
in the form of a plate, a light-diffusion plate
5
, and the light source unit
4
. They are arranged in parallel with one another in facing relation to one another.
The liquid crystal panel
2
is supported by being sandwiched between the shield front
31
and a shield center
32
. The light-diffusion plate
5
and the light source unit
4
are supported by being sandwiched between the shield center
32
and the shield rear
33
.
The heat radiator
7
and the parts
8
are mounted on a rear surface of the shield rear
33
.
The shield front
31
, the shield center
32
and the shield rear
33
are coupled to one another through screws.
Hereinbelow is explained a structure of the light source unit
4
. A structure of the light source unit
4
is grouped into a beneath-arrangement type and a side light type.
FIG. 2A
is a cross-sectional view of a liquid crystal display device including a beneath-arrangement type light source unit, and
FIG. 2B
is a cross-sectional view of a liquid crystal display device including a side light type light source unit.
As illustrated in
FIG. 2A
, a beneath-arrangement type light source unit
4
is comprised of a reflector
43
positioned in a dish-shaped portion
4
a
(lamp house) of the shield rear
33
, a plurality of pillar-shaped light sources
41
near and along the reflector
43
, and a light-diffusion plate (not illustrated) covering the lamp house
4
a
and spaced away from the light sources
41
.
The light-diffusion plate prevents non-uniformity in brightness.
As illustrated in
FIG. 2B
, a side light type light source unit
4
is comprised of a light-guide plate
42
in the form of a plate, a pillar-shaped light source
41
located adjacent to a side of the light-guide plate
42
, and a reflector
43
surrounding the light source
41
.
The light-guide plate
42
is composed of highly light-permeable acrylic plate. A light emitted from the light source
41
passes through the light-guide plate
42
, and illuminates a rear surface of the liquid crystal panel
2
through an opening
32
a
formed with the shield center
32
.
Dots are printed over a rear surface of the light-guide plate
42
facing the shield rear
33
in order to prevent non-uniformity in brightness.
Japanese Unexamined Patent Publication No. 10-172512 has suggested a light source unit which prevents an increase in temperature in an object to which a light is to be radiated.
As illustrated in
FIG. 3
, the suggested light source unit
4
includes a light source
41
comprised of an elongate glass bulb containing an electrically discharging medium, and an outer glass pipe
49
spaced away from the light source
41
to thereby define a vacuum layer
41
b
therebetween. A light emitted from the light source
41
passes through an entire surface
41
a
of the glass bulb
41
, and heat radiated from the light source
41
through the entire surface
41
a
is absorbed in the vacuum layer
41
b
. Thus, it would be possible to reduce heat radiation to an object which is to be illuminated by the light source
41
.
As mentioned earlier, if a brightness at a display surface of a liquid crystal display device is to be increased, heat radiation to a liquid crystal panel from a light source unit would be increased in dependence on an increase in the brightness.
Hence, the heat radiation has to be suppressed in order not to deteriorate a brightness and a display quality of a liquid crystal panel.
However, the conventional liquid crystal display device including a heat radiator mounted on a rear surface of a shield could be improved only in that the shield and/or heat radiator are(is) composed of material having high thermal conductivity, or that the heat radiator is designed to have a surface area as wide as possible.
In accordance with the light source unit suggested in the above-mentioned Japanese Unexamined Patent Publication No. 10-172512, interruption of heat to an object (liquid crystal panel) from the light source unit could be obtained to some degree. However, only such adiabatic effect could accomplish just a limited increase in output power of the light source unit.
Specifically, if an output power of the light source unit is increased, a temperature in the glass bulb
41
would be raised more than necessary due to heat interruption from an atmosphere, resulting in reduction in a light-emitting efficiency and reduction in a lifetime caused by degradation of phosphor and/or electrodes.
If the above-mentioned light source unit is applied to a side light type light source unit, multiple reflection would occur to the reflector
43
, resulting in light loss.
In
Hodges Matt
NEC LCD Technologies Ltd.
Young & Thompson
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