Illumination – Revolving
Reexamination Certificate
2002-12-18
2004-10-26
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S561000, C362S558000, C362S026000, C349S062000, C349S065000, C349S064000
Reexamination Certificate
active
06808282
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to an illumination device, and more particularly, to an illumination device disposed near a side of a liquid crystal panel.
2. Related Art
Illumination devices also known as front lights are positioned on a front side of a reflection type liquid crystal display. The front lights are positioned above a viewer's side of a liquid crystal panel to illuminate a liquid crystal panel.
FIG. 12
is a sectional view of a liquid crystal display
100
having a front light
110
positioned on a front side of a liquid crystal panel
120
. In the illustrated liquid crystal panel
120
, a liquid crystal layer
123
secured by a sealant
124
is positioned between a top substrate
121
and a bottom substrate
122
. A liquid crystal control layer
126
is positioned on an inner surface of the top substrate
121
. A reflection layer
127
having a high reflectance is positioned below a liquid crystal control layer
128
.
As shown, the front light
110
includes a flat light guide plate
112
and a light source
113
positioned directly adjacent to a side end face
112
a
. A portion of the light emitted from the light source
113
is received by the light guide plate
112
at the side end face
112
a
. The light is reflected by a reflecting surface
112
c
that includes a prism that changes the propagating direction of the light.
An anti-reflection layer
117
is positioned directly adjacent to an exit surface
112
b
, which allows light to be directed toward the liquid crystal layer
123
. The anti-reflection layer
117
prevents reflected light within the reflection type liquid crystal panel
120
from being further reflected within the light guide plate
112
.
In some devices a plurality of layers having different refractive indices such as layers made of SiO2 and TiO2 form the anti-reflection layer
117
. This anti-reflection type layer is formed by a sputtering and vacuum deposition method. The method can provide a 1/4&lgr; optical condition, which allows light to be transmitted with a high transmittance ratio.
The above-described method for forming the anti-reflection layer
117
can have many problems. One problem is that the vacuum deposition and sputtering methods have a low yield and a high manufacturing cost. The high cost arises, in part, because these methods are processed in batch. Since the anti-reflection effect is provided by a combination of reflective indices and layer thicknesses, it can be difficult to achieve an anti-reflection effect for all visible wavelengths. Moreover, when an illumination device having such an anti-reflection layer is observed from a diagonal position, the anti-reflection layer
117
can appear with a colored tint that diminishes the quality of a displayed image.
Durability can also become problem since the above-described anti-reflection layer
117
is made of multiple layers. Multiple layers are especially susceptible to environments having a high temperature and a high humidity. Such conditions can affect the reliability of the light guide plate
112
and the front light
110
.
To improve productivity, a method of making an anti-reflection layer has been proposed that uses an organic compound having a relatively low refractive index. In this concept, an immersion process uses a material whose refractive index can be arbitrarily changed and from which a practical processing liquid can be produced. Unfortunately, it is difficult to form an anti-reflection layer that can provide a high anti-reflection effect because there are few materials that can adequately control the refractive index and are easy to produce. Further, to achieve a practical anti-reflection effect, the application of the organic compound to the light guide plate must be followed by post-processes such as a heating process, which deteriorates the characteristics of the light guide plate.
SUMMARY
A light guide plate comprises a structure that receives light at a side end face, facilitates light propagating therein, and conveys light through an exit surface. Preferably, an anti-reflection layer is coupled to the exit surface. In one embodiment, the anti-reflection layer comprises microscopic recesses and/or projections. Theses recesses and/or projections can be a submicron in lenght and/or arranged like a lattice on the exit surface.
In a light guide plate embodiment, microscopic concave and/or convex features about equal to or smaller than the wavelength of visible light are arranged or formed on the exit surface of a light guide plate. Preferably, the concave and/or convex features prevent light incident to an exit surface from being reflected, thereby improving the transmittance ratio at the exit surface. The light guide plate allows light propagating in the light guide plate to pass through the exit surface at a high efficiency. When combined with a light source, this embodiment encompasses a high intensity illumination display.
In a second light guide plate embodiment, the anti-reflection layer comprises microscopic recesses and/or projections preferably having a pitch of about 0.3 &mgr;m or less. Preferably, this configuration allows shorter wavelength light to be sufficiently transmitted, thereby providing an anti-reflection effect. When the pitch exceeds 0.3 &mgr;m in this embodiment, a portion of the light traveling though the light guide plate is reflected, which reduces the transmittance ratio at the exit surface. While the effect of preventing reflection of light in this embodiment becomes more significant the smaller the pitch, the pitch is preferably about 0.2 &mgr;m.
In a third light guide plate embodiment, the microscopic recesses and/or projections are arranged in a staggered lattice. Such a configuration allows a higher density of recesses and/or projections than that of the tetragonal lattice arrangement and embodiment. Preferably, the microscopic recesses can be arranged with a small effective pitch, which improves the anti-reflection effect and prevents light transmitted or reflected by the anti-reflection layer from being tinted.
In a fourth embodiment, the recesses and/or projections formed in a staggered arrangement are preferably arranged in a direction in which the effective pitch of the recesses or projections is minimized in a main light guide direction. Such a configuration provides an improved anti-reflection effect.
“An effective pitch” is equivalent to the distance between a first straight line that passes through the center of a certain projection (recess) and a second straight line that passes through the center of a projection (recess) adjacent to the projection (recess) and is parallel to the first straight line. The effective pitch of the plurality of projections arranged like a tetragonal lattice in an arranging direction of the projections is the same as the pitch of those projections. The effective pitch in the diagonal direction of the tetragonal lattice is ½ of the pitch of the projections and is slightly smaller than the actual pitch. Further, when the projections of the anti-reflection layer are arranged in a highest density in a staggered arrangement like a hexagonal lattice, the effective pitch is as small as about ½ of the actual pitch.
The “main light guide direction in the plane of the light guide plate” is a macroscopic propagating direction of light introduced into the light guide plate from the light source positioned near a side end face of the light guide plate. The main light guide direction is normally a direction from the side end face where the light source is positioned toward a second side end face that is across from it.
In one light guide plate embodiment, the effective pitch of the recesses and/or projections in the main light guide direction in the plane of the light guide plate is preferably about 0.15 &mgr;m or less. Such a configuration provides a light guide plate that achieves an improved anti-reflection effect and which prevents light transmitted or reflected thereby from being tinted.
A method of manufacturing a light guide plate in
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Husar Stephen
Zeade Bertrand
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