Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-06-15
2003-11-18
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
Reexamination Certificate
active
06650382
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective type liquid crystal display apparatus that is used for a display function of information display systems, office automation equipment, etc. Specifically, the present invention relates to a reflective type liquid crystal display apparatus including a front light for efficiently illuminating a liquid crystal display device without deteriorating the display quality thereof. Such a display apparatus is therefore preferable for use in portable information terminals or equipment for mobile computing. The present invention also relates to portable electric equipment including such a reflective type liquid crystal display apparatus.
2. Description of the Related Art
In general, liquid crystal display apparatus can be divided into two groups: a group of transmissive type liquid crystal display apparatus which display letters, images, etc., by adjusting the amount of transmitted light which is emitted from a particular light source; and a group of reflective type liquid crystal display apparatus which display letters, images, etc., using ambient light.
The transmissive type liquid crystal display apparatus includes a light source such as a fluorescent light, an electroluminescence (EL) device, or the like, placed on the back surface of a liquid crystal device as a planar light source (backlight). On the other hand, the reflective type liquid crystal display apparatus does not require a backlight because it displays images using ambient light. Thus, the reflective type liquid crystal display apparatus enjoys advantages such as light weight, thin shape, low power consumption, etc. Furthermore, in a highly bright environment in which sunlight is incident directly on the display device, the reflective type liquid crystal display apparatus enables a viewer to observe images more clearly, whereas the transmissive type liquid crystal display apparatus exhibits serious deterioration in the visibility of images. Thus, demands for the reflective type liquid crystal display apparatus have been increasing, and such a reflective type device is more likely for application in portable electronic equipment such as portable information terminals or apparatus for mobile computing.
However, it is sometimes impossible for the reflective type liquid crystal display apparatus to provide sufficient display in a dark environment such as nighttime or the like because the reflective type liquid crystal display apparatus uses ambient light for display and the display brightness thereof heavily depends on environmental conditions. Specifically, such a drawback is a major problem in a reflective type liquid crystal display apparatus which uses a color filter for displaying color images or in a reflective type liquid crystal display apparatus which uses polarizing plates.
In order to address such a drawback, it has been proposed to provide an illumination device called a front light for illuminating, in the case of insufficient ambient light, a reflective type liquid crystal device from the front face thereof.
For example, CX. PAL Vol. 40 (Sony Semiconductor News pp. 26-27) describes an example of such a front light. This document discloses a conventional front light including a light guide for converting a light from a light source into planar emission light, and an optical film composed of a polarizing plate and a quarter-wave plate which are combined and placed on the emission surface side of the light guide.
However, the above-described conventional art involves the drawbacks described below.
In general, an electronic information apparatus is covered with a case (a protection element) for protecting a liquid crystal display device. The case is provided with a window through which a viewer observes a display screen. For example, referring to
FIG. 11A
, in a reflective type liquid crystal display apparatus
450
, a window
401
a
is formed in a size larger than a display area
402
which corresponds to a plurality of pixels formed in the reflective type liquid crystal display device.
The window
401
a
is designed so that an unobservable display area does not occur (i.e., the entire display area
402
can be seen) even when observed from an oblique direction. This is because peripheral portions
402
y
of the display area
402
cannot be seen when a viewer
400
observes the display area
402
through the window
401
a
from an oblique direction (a direction not vertical to the screen) as shown in FIG.
11
B. The window
401
a
is typically formed larger than the display area
402
by about 1 mm in each direction, in consideration of an attachment margin as well as an unobservable display area
402
y.
In a reflective type liquid crystal display apparatus including a front light (an illuminator) for illuminating a reflective type liquid crystal display device, the front light and the liquid crystal display device are covered with a case, and a window is formed in a viewer-side face of the case through which the viewer observes the screen of the liquid crystal display device.
In such a structure, when the size of the light guide is too large relative to the size of the window, electronic equipment becomes large, and the portability thereof may therefore deteriorate. Furthermore, in the case where the size of the light guide of the front light is smaller than the size of the window, light leaks from end faces of the light guide when the light is on, which is observable by the viewer. As a result, display quality of the liquid crystal display apparatus significantly deteriorates.
Furthermore, in the case where an optical film is provided under a lower surface of the light guide (an opposite side to the viewer), especially when an adhesion layer is provided between the light guide and the optical film, light leaks from the end faces of the light guide, end faces of the optical film, and an interface between the adhesion layer and the light guide. As a result, display quality significantly deteriorates.
Yet, CX. PAL Vol. 40 (Sony Semiconductor News pp. 26-27) does not disclose any means of solving such problems.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a reflective type liquid crystal display apparatus includes: a reflective type liquid crystal display device for displaying images by reflecting incident light in such a manner that the incident light is separately controlled for each pixel; a front light positioned at a front face side of the reflective type liquid crystal display device, the front light including a light source and a light guide, wherein light emitted from the light source enters the light guide from an end face thereof near the light source, and the light is output from a large face of the light guide which faces the liquid crystal display device; and a protection member for covering the reflective type liquid crystal display device and the front light, wherein a window is formed in the protection member at a front face side of the front light for a viewer to observe the images displayed on the reflective type liquid crystal display device, wherein, at a side of the front light in which the light source is not provided, a distance between an end face of the window formed in the protection member and an end face of light guide adjacent thereto is determined so that light incident in a direction within a desirable viewing angle range passes through a lower face of the light guide.
In one embodiment of the present invention, the protection member covers an end portion of the light guide such that distance X
1
between an end face of the window and an end face of the light guide is within the following range:
0
≦
X1
≦
∑
i
=
1
g
(
t
i
+
1
/
tan
(
90
°
-
sin
-
i
(
(
n
i
/
n
i
+
1
)
X
sin
θ
i
)
)
)
(where t
i+1
is a thickness of the (i+1)th layer; n
i
and n
i+1
are refractive indices of the i-th layer and the (i+1)th layer, respectively; angle
Ebi Tsuyoshi
Masuda Takeshi
Sumida Yukihiro
Parker Kenneth
Sharp Kabushiki Kaisha
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