Illumination – Revolving
Reexamination Certificate
2001-03-30
2003-12-02
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S560000, C362S561000, C362S562000, C362S318000
Reexamination Certificate
active
06655810
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a backlight unit to be used in liquid crystal displays, etc.
The invention also relates to a backlight unit in which the light source unit is filled with a transparent liquid.
The invention also relates to a reflector structure that realizes high-luminance and high-efficiency sidelight-type backlight units.
The invention also relates to a cold-cathode tube usable for a light source that receives essentially the fluorescence of the UV rays having been emitted through discharge emission of mercury or the like and emits visible light, especially for the light source of that type for liquid crystal displays.
2. Description of the Related Art
Recently, liquid crystal display panels have been rated highly in the market, as they save space upon installation and save power during operation, and their applications are expanding not only for displays of portable computers and monitors for portable televisions, but also for monitors of desk-top personal computers and flat televisions in domestic use. The backlight unit for lighting the liquid crystal display surface of such a liquid crystal display panel from the back surface of the panel includes two types; one being a direct-light-type unit that comprises a diffuser, a cold-cathode tube and a reflector all disposed just below the back surface of a liquid crystal display panel, and the other being a sidelight-type unit that comprises a diffuser, an optical waveguide and a reflector all disposed just below the back surface of a liquid crystal display panel, in which a cold-cathode tube and a reflector having a C-shaped or rectangularly U-shaped cross section are disposed on both sides of the optical waveguide.
For downsizing them and saving space upon installation, the latter is preferred to the former. However, the luminance of the former direct-light-type unit could be easily increased merely by increasing the number of the cold-cathode tubes in the unit, but it is difficult to increase the number of the cold-cathode tubes in the latter sidelight-type unit. It is therefore desired to increase the luminance of sidelight-type backlight units by increasing the emission efficiency of the units.
Prior Art 1
A sidelight-type backlight unit having a structure shown in FIG.
37
A and
FIG. 37B
is generally used for liquid crystal display monitors.
FIG. 37A
is a view of a backlight unit of that type seen on its emission side.
FIG. 37B
is a cross-sectional view of
FIG. 37A
cut along the line A—A. As illustrated, the backlight unit comprises an acrylic plate
100
(this serves as an optical waveguide) with a light-scattering pattern
114
formed on its back surface, and two cold-cathode tubes
102
,
104
disposed nearly in parallel with each other on and along one side of the acrylic plate
100
. A reflector
110
(for this, an aluminum film is popularly used) is provided to surround the two cold-cathode tubes
102
,
104
, and its one side is opened to the optical waveguide
100
facing thereto. Also on and along the other side of the optical waveguide
100
having the two cold-cathode tubes
102
,
104
disposed on its one side, other two cold-cathode tubes
106
,
108
are disposed nearly in parallel with each other, and a reflector
112
is provided to surround the two cold-cathode tubes
106
,
108
with its one side being opened to the optical waveguide
100
facing thereto.
In case where the number of the cold-cathode tubes in the sidelight-type backlight unit is increased for increasing the luminance of the unit, it produces some problems. One problem is the efficiency in light emission to the optical waveguide; and the other is the temperature of the cold-cathode tubes. Increasing the number of the cold-cathode tubes in the limited space in the unit inevitably makes the tubes more tightly adjacent to each other. As a result, in some region in the unit, the neighboring tubes will partly absorb the light emitted by them, thereby lowering the emission efficiency of the unit. In addition, in the area in which such an increased number of cold-cathode tubes are tightly aligned, the atmospheric temperature will increase, and if so, the tubes must be cooled so as to keep them at a temperature at which they ensure the maximum luminance.
In addition, the cold-cathode tubes in the unit involve by themselves a factor to lower the emission efficiency of the unit. As in
FIG. 38
, for example, the light emitted from one point of a cold-cathode tube
108
is partly reflected on the outer surface of the glass tube
136
. In a cold-cathode tube having, for example, an outer diameter of 2.6 mm and an inner diameter of 2.0 mm, the reflected light accounts for at least 30% of the entire light emission from the tube. About 25% of the reflected light having reached the inner surface of the glass tube (for example, on the point c and the point d in
FIG. 38
) will be absorbed by the phosphor
138
coated on the inner surface of the glass tube or by the mercury gas filled in the glass tube. In addition, when the light from the cold-cathode tube
108
enters the glass tube of the neighboring cold-cathode tube
106
, about 25% of the incident light that reaches the inner surface of the glass tube (for example, on the point a and the point b in
FIG. 38
) will be absorbed by the phosphor
138
coated on the inner surface of the glass tube or by the mercury gas filled in the glass tube.
To solve the prior art problems noted above, a method is proposed, which comprises filling the outer peripheral space of a cold-cathode tube with a liquid of which the refractive index is nearly the same as that of the glass material that forms the outer wall of the cold-cathode tube. According to this method, the reflection on the outer surface of the cold-cathode tube can be reduced, and, in addition, the incident light to the neighboring cold-cathode tube can be also reduced. Therefore, the method will be effective for increasing the emission efficiency of backlight units. In addition, since the liquid filled in the space around the cold-cathode tube will act also as a coolant, another advantage of the method is that the method does not involve the problem of temperature elevation even through a large number of cold-cathode tubes are packaged in the unit.
Prior Art 2
One conventional structure of a liquid crystal display with a sidelight-type backlight unit used therein is described, for which referred to is FIG.
41
. As illustrated, a backlight unit is disposed adjacent to the emission side of a liquid crystal panel
134
. The backlight unit is composed of a light source unit that comprises cold-cathode tubes (fluorescent tubes)
102
to
108
and reflectors
110
,
112
; and an optical waveguide unit that comprises a diffuser (optical sheet)
130
, an optical waveguide
100
and a reflector
132
. As the case may be, the diffuser
130
may have a multi-layered structure of plural sheets, depending on the mode of light diffusion through the optical waveguide unit.
For increasing the luminance of the backlight unit, two cold-cathode tubes of
102
to
108
are disposed for each of the reflectors
110
,
112
, and the optical waveguide
100
therefore has two pairs of cold-cathode tubes on both of its sides. The light emitted by the cold-cathode tubes
102
to
108
toward the optical waveguide
100
directly enters the optical waveguide
100
through its sides, and it is transmitted within the waveguide while being almost entirely reflected on and around it. The light emitted by the cold-cathode tubes
102
to
108
toward the reflectors
110
,
112
is reflected by the reflectors
110
,
112
, and the thus-reflected light also enters the optical waveguide
100
through its sides and is transmitted within it like the direct light above.
Passing through the optical waveguide, a part of the light L
1
goes out toward the reflector
132
or toward the diffuser
130
, and the light that reaches the diffuser
130
passes through it while been diffused therethrough toward the liquid crystal
Gotoh Takeshi
Hamada Tetsuya
Hayashi Keiji
Kobayashi Tetsuya
Sugawara Mari
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
O'Shea Sandra
Payne Sharon
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