Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1999-02-18
2002-04-09
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S062000, C349S063000, C349S065000, C349S057000, C349S058000
Reexamination Certificate
active
06369866
ABSTRACT:
The present invention relates to liquid crystal displays, and more particularly, to liquid crystal displays having mechanisms that collect ambient light to illuminate the display.
A liquid crystal display (LCD) includes pairs of opposing transparent electrodes, and liquid crystal, which is contained between the electrodes. The liquid crystal is electro-optically anisotropic. The application of a predetermined voltage between the electrodes forms an electric field with the liquid crystal. This causes the liquid crystal to exhibit optical properties that correspond to the field density. The LCD has a plurality of pixels. An image is formed by applying a different voltage to each pixel so that the pixel obtains the desirable brightness. A typical LCD employs a backlight to illuminate the display from behind.
In addition to a compact and thin profile, an LCD has low power consumption. Thus, LCDs are often used in office automation equipment and audio visual equipment. Portable equipment having LCDs are often used outdoors, where ambient light is abundant. In such cases, the ambient light may be used in lieu of the backlight to further decrease power consumption by a significant amount.
A prior art LCD will now be described with reference to
FIG. 1
, which is a cross-sectional view showing an LCD
100
.
The LCD
100
has a display panel
10
, a backlight
80
arranged behind the display panel
10
, and a case
70
housing the display panel
10
and the backlight
80
. The backlight
80
includes a light guide plate
20
, a light source
50
arranged on one end of the light guide plate
20
, a collecting lens
60
arranged on the other end of the light guide plate
20
, a diffusing portion
30
arranged on a front side of the light guide plate
20
, and a reflecting portion
40
arranged below or on the rear side of the light guide plate
20
.
The light source
50
, which may be a fluorescent lamp, is encompassed by a reflector
51
. The light guide plate
20
may be made of acrylic resin. A convex lens, which is formed separately from the light guide plate
20
or integrally with the light guide plate
20
, may be employed as the collecting lens
60
. The case
70
has an opening
71
, which is located at a position corresponding to the collecting lens
60
which allows the collecting lens
60
to project outward through the opening
71
to allow the collecting lens
60
to collect light from outside of the case
70
.
Light, which is emitted by the light source
50
or collected by the collecting lens
60
, is transmitted to the light guide plate
20
. The light is then refracted by the light guide plate
20
toward the diffusing plate
30
or the reflecting portion
40
. The reflecting portion
40
may be a plate, a film or a coating including a reflecting surface. The diffusing portion
30
may also be a plate, a film or a coating including a diffusing surface. The reflecting portion
40
reflects the light toward the diffusing portion
30
through the light guide plate
20
. The diffusing portion
40
diffuses the light so that some of the light forms an even light plane that is irradiated toward the display panel
10
, while the remaining light is returned toward the light guide plate
20
to be reflected again by the reflecting portion
40
. Accordingly, the intensity of the light attenuates as it bounces back and forth horizontally between the diffusing portion
30
and the reflecting portion
40
.
The display panel
10
does not emit light by itself. Thus, the display panel
10
is illuminated from behind. The light permeability of the display panel
10
is controlled in order to distribute the light passing through the display panel
10
in a desired pattern so that images can be visualized on the display panel
10
.
The light source
50
is lit to illuminate a bright image on the display panel
10
when ambient light is insufficient, such as during indoor usage. The light source
50
is turned off when ambient light is abundant, such as during outdoor usage on a sunny day. Under such conditions, the light collected by the collecting lens
60
is used to illuminate the display panel
10
. Thus, although power for driving the display panel
10
is still necessary, power for driving the light source
50
becomes unnecessary. This reduces the total power consumption of the LCD
100
.
The relationship between brightness relative to positions on the display panel
10
during sole usage of the collecting lens
60
, is shown in the graph of FIG.
2
. The horizontal axis represents the lateral position on the display panel
10
, while the vertical axis represents the brightness. Position A indicates the illuminated right end on the display panel
10
that is closest to the collecting lens
60
and position B indicates the illuminated left end of the display panel
10
. The light collected by the collecting lens
60
travels from position A to position B, as viewed in the graph of FIG.
2
. As shown in the graph, there are several brightness peaks. The value of the peak closest to position A is maximum, and the values of the other peaks decrease as the distance from position A increases.
The distance between adjacent peaks is determined by the size of the illuminated portion on the display panel
10
. For example, in a two inch LCD, the width of which is 45 millimeters, the distance between adjacent peaks is approximately 15 millimeters. In a fifteen inch LCD, the width of which is 190 millimeters, the distance between adjacent peaks is approximately 60 millimeters. Such peaks, or brightness fluctuation, results in the illumination of visual brightness stripes and lowers the quality of the En image illuminated on the display panel
10
.
Accordingly, it is an objective of the present invention to provide an LCD having uniform brightness.
SUMMARY OF THE INVENTION
To achieve the above objective, the present invention it provides a liquid crystal display comprising a liquid crystal display panel, a light guide plate arranged adjacent to the display panel, a light transmitter optically connected to the light guide plate, and a light collector optically connected to the light transmitter.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 5101325 (1992-03-01), Davenport et al.
patent: 5121232 (1992-06-01), Miyadera
patent: 6011602 (2000-01-01), Miyashita et al.
patent: 6025897 (2000-02-01), Weber et al.
patent: 6034750 (2000-03-01), Rai
patent: 6104454 (2000-08-01), Hiyama et al.
patent: 6147725 (2000-11-01), Yuuki et al.
Marushita Yasushi
Rai Yasuki
Shimizu Makoto
Uehara Hisao
Qi Mike
Sanyo Electric Co,. Ltd.
Sheridan & Ross P.C.
Sikes William L.
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