Illumination – Revolving
Reexamination Certificate
1997-09-11
2003-09-02
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S026000
Reexamination Certificate
active
06612709
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention generally relates to lighting devices, and more particularly to a lighting device applied to a back-lighting device of a transmitted type liquid crystal display device.
Recently, a display unit has widely been employed in wordprocessors, personal computers or the like together with improvements in the display capacity and lighting performance. Further, it has been required to provide thin and light display units applicable to notebook-type devices and workstations using a large-size display. Particularly, there has been considerable activity in the development of high-luminance color display units. Under these situations, it has been necessary to provide high-luminance, high-efficiency lighting devices.
An edge light type back-lighting device has been applied to a liquid crystal display device. In such a type of back-lighting device, light is incident to a side surface of a transparent light conducting plate. The incident light is propagated through the light conducting plate so that the light is totally reflected at an interface of the light conducting place. The light conducting plate has a slope at its center portion, and is provided with white ink portions. Hence, the condition for total reflection is broken and the light is emitted via a light-emitting surface.
FIG. 1
is a diagram of a conventional edge-light type lighting device
90
, which includes two fluorescent tubes
81
, a light conducting plate
82
made of a transparent resin, incident surfaces
82
a
of the light conducting plate
82
, a back surface
82
b
of the light conducting plate
82
on which a diffusion reflection pattern is printed, a light-emitting surface
82
c
of the light conducting plate
82
, a reflection sheet
83
, an emission surface
84
, reflection mirrors
85
respectively enclosing the fluorescent tubes
81
, a linear prism
86
, a transparent diffusion sheet
87
and an inner propagation light
88
and an emitted light
89
.
As shown in
FIG. 1
, the fluorescent tubes
81
covered by the reflection mirrors
85
are arranged so that lights emitted therefrom enter into the incident surfaces
82
a
of the light conducting plate
82
. The light conducting plate
82
has slopes from the incident surfaces
82
a
so that the light conducting plate
82
becomes thinner toward the center thereof from the incident surfaces
82
a
. These slopes of the light conducting plate
82
form the light-emitting surface
82
c
. The diffusion reflection pattern which has a weighted white-ink pattern is formed on the back surface
82
b
so that the printed area of the pattern is increased as the distances from the fluorescent tubes
81
increase. The reflection sheet
83
provided on the surface opposite to the back surfaces
82
b
functions to efficiently and effectively emit light scattered by the diffusion reflection pattern. The linear prism
86
is provided on the emission surfaces
84
of the light conducting plate
82
in order to effectively collect the emitted light
89
in the normal line direction. Further, the diffusion sheet
87
which prevents the diffusion reflection pattern from being seen from the outside of the lighting device is disposed on the emission side of the linear prism
86
.
The diffused lights emitted from the fluorescent tubes
81
enters into the incident surfaces
82
a
of the light conducting plate
82
and are propagated through the light conducting plate
82
while the condition for total reflection is satisfied. The angle of the inner propagation light
88
becomes sharp by an angle &THgr; of the light-emitting surface
82
c
each time the inner propagation light
88
is totally reflected. When the angle of the inner propagation light
88
becomes greater than the critical angle, the light is emitted via the light-emitting surface
82
c
as the emitted light
89
. The inner propagation light
88
totally reflected by the light-emitting surface
82
c
reaches the back surface
82
b
is emitted via the emission surface
84
because the diffusion reflection pattern breaks the condition for total reflection.
However, the prior art lighting device has the following disadvantages. All lights emitted from fluorescent tubes
81
are not emitted via the emission surface
84
. Some light emitted from one of the fluorescent tubes
81
is propagated through the light conducting plate
82
and is returned to the associated reflection mirror
85
. At this time, the returned light hits the reflection mirror
85
and loss of light occurs. Hence, the efficiency in use of light is not good. This problem may be reduced by means of the sloped light-emitting surface
82
c
of the light conducting plate
82
. However, it has not been possible to obtain sufficient and satisfactory lighting performance.
The linear prism plate
86
disposed between the light conducting plate
82
and the diffusion sheet
87
contributes to a reduction in the above loss of light to enhance luminance in the normal line direction. However, an interference will occur unless the pitch of linear prisms of the linear prism plate
86
is optimally selected with respect to the pitch between electrodes arranged in rows and columns of a display panel. Hence, in practice, the diffusion sheet
87
having a high degree of diffusion is used or optimal pitches of the linear prisms are selected with respect to the respective electrode pitches. However, the luminance in the normal line direction is decreased as the degree of diffusion is increased. Further, dies for the respective pitches of the linear prisms must be prepared, which leads to an increase in the production cost.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a lighting device in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a thin, light and efficient lighting device having a high uniform luminance distribution.
The above objects of the present invention are achieved by a lighting device comprising: a light source; a light conducting plate having an incident surface receiving light emitted from the light source, a back surface and a light-emitting surface; and a reflection member having a first portion facing the back surface, and a second portion located on a side opposite to a side of the light conducting plate on which the light source is located, the second portion being spaced apart from the light conducting plate so that light emitted from the light conducting plate is oriented toward an emission surface of the lighting device.
The above objects of the present invention are also achieved by a lighting device comprising: a light source; a light conducting plate having an incident surface receiving light emitted from the light source, a back surface and a light-emitting surface; and a reflection member having a first portion facing the back surface, and a second portion located on a side opposite to a side of the light conducting plate which the light source is located, the light conducting plate comprising a plurality of concave portions which are formed on the back surface and orient light emitted from the light conducting plate via the back surface toward an emission surface of the lighting device, a parameter related to the plurality of concave portions being weighted so that an even luminance distribution can be obtained on the emission surface.
The above objects of the present invention are also achieved by a lighting device comprising: a plurality of units located on a plane; the plurality of units respectively comprising: light sources; light conducting plates, each having an incident surface receiving light emitted from the light sources, a back surface, a light-emitting surface and an edge opposite to the incident surface; and a reflection member facing the back surfaces of the light conducting plate.
The above objects of the present invention are also achieved by a lighting device comprising: a plurality of units located; the plurality of units respectively comprising: light sources;
Miyahara Masaki
Nagatani Shinpei
Nittou Eiji
Yamada Fumiaki
Arent Fox Kintner Plotkin & Kahn
Fujitsu Display Technologies Corporation
Husar Stephen
LandOfFree
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