Illumination – Revolving
Reexamination Certificate
2002-10-23
2004-11-30
Cariaso, Alan (Department: 2875)
Illumination
Revolving
C362S327000, C362S330000, C362S331000, C385S088000, C385S146000, C385S147000
Reexamination Certificate
active
06824285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light source used in a display device, a sensor, a scanner, a printer and the like, and particularly relates to a light source used as an illuminating means of a liquid crystal display device and to a liquid crystal display device using these light sources.
2. Description of Related Art
As an illuminating means of a liquid crystal display device, several methods using a tube-shaped lamp such as a cold cathode ray tube or an LED (light emitting diode) as a primary light source (light source emitting light by itself) are in use. In case of combining a liquid crystal panel of a transmission type with a tube-shaped lamp, as shown in
FIG. 2
, a structure in which a tube-shaped lamp
21
covered with a reflector
22
is arranged at one side of a planar light guide
24
and a reflecting plate
23
is arranged at the back of the planar light guide
24
, and a diffusing plate
25
is arranged at the entrance face side is made to be the mainstream from the viewpoint of space saving. And in case of combining a liquid crystal panel of a reflection type with a tube-shaped lamp, a structure in which a tube-shaped lamp covered with a reflector is arranged at one side of a planar light guide and the planar light guide is arranged at the observer side of the liquid crystal panel of a reflection type is formed.
The use of an LED as a primary light source is superior to a tube-shaped lamp from the viewpoint of power saving and space saving. However, it is difficult to obtain a uniform light emission as a planar light guide since the light emitting face of an LED is small.
Several methods for solving this problem are known. For example, as shown in
FIG. 3
disclosed in Japanese Patent Laid-Open Publication No. 10-260,405 (reference 1), a uniform light emission is obtained by arranging a linear light guide
32
for spreading light from an LED
31
in the shape of a line between the LED
31
and a planar light guide
24
(FIG.
3
). And as disclosed in Japanese Patent Laid-Open Publication No. 11-231,320 (reference 2), there is also a method of disposing a linear light guide and forming an array of projections on the entrance face of a planar light guide. Further, as a method of using no linear light guide, there is mentioned a method of providing a blind hole
41
depressed in the direction of thickness having a function of refracting and reflecting light emitted from a light source in a light guide member, as disclosed in
FIG. 4
in Japanese Patent Laid-Open Publication No.2001-23,423 (reference 3).
By using these methods, it is possible to obtain uniform light emission, so that the planar light guide can be combined with a liquid crystal panel as an illuminating means in a similar manner to the case of a tube-shaped lamp.
In the above-mentioned techniques, the angular distribution of emergent light is so wide that a large amount of the light is not used efficiently. For example, a white LED of chip type used in a liquid crystal display device for a mobile information terminal emits light with distribution of about ±60°, which is much wider than the field of view of an observer. In case that light
51
having such a distribution is incident on a linear light guide or a planar light guide as disclosed in reference 1 or 2 (FIG.
5
(
a
)), the light outputted from the planar light guide has a similar angular distribution (emergent light angular distribution) to the incident light (using such a projection structure as shown in reference 2 makes the emergent light angular distribution more spread). Further, since light from a liquid crystal display panel to an observer
56
has also a similar angular distribution, the amount of light incident on an eye of the observer becomes small (FIG.
5
(
b
)).
In short, the efficiency of utilizing light is lowered. This becomes a problem in particular in a liquid crystal display device for a mobile information terminal in which space and power saving are demanded. In FIG.
5
(
a
), symbol
32
is a linear light guide, symbol
52
is emergent light from the linear light guide, symbol
53
is a liquid crystal panel of a reflection type, symbol
54
is emergent light from a planar light guide, symbol
55
is reflected light for displaying on the liquid crystal panel of a reflection type, symbol
56
is an observer, and symbol
57
is light to come into an eye of the observer.
As a method for solving this problem, there is a method mentioned in Japanese Patent Laid-Open Publication No.2000-315,413 (reference 4). In reference 4 (FIG.
6
), a collimating structure covered with a light reflecting plate
61
is shown. The structure has a part that is wide at the light guide side and narrow at the light source side. However, it is required to form a number of said complicated collimating structures between the light source and the light guide. In
FIG. 6
, symbol
62
is incident light from the light source and symbol
63
is emergent light from the collimating means.
As a method for narrowing the emergent light angular distribution, there is a method of affixing a lens to an LED. However, a light source is required to be far smaller than the lens (the light source is at least {fraction (1/10)} relative to the lens) (FIG.
7
(
a
)). For example, in case that a light source
31
and a lens
71
are close in size as shown in FIG.
7
(
b
), light goes through with various angles, so that a large part of light
72
cannot be used efficiently. Therefore, the method of affixing a lens to an LED requires a lens to be very large in comparison with the size of an LED and is difficult to be used as an illuminating means of a liquid crystal display device from the viewpoint of space saving.
As a method of using a lens shape, it is difficult also to apply a structure of combining a lens face
84
with a total reflection surface
83
(FIG.
8
(
a
)) disclosed in “a paper by Singo Tamai et al., pp.1,247 in a collection of papers read at the Electronics Society Convention 2000, the Institute of Electronics, Information and Communication Engineers of Japan” (reference 5) to an illuminating means of a liquid crystal display device (FIG.
8
(
b
)), since the combined structure needs a much larger lens shape in comparison with the size of an LED in the same way as described above.
Although it is conceivable also to use an LED disclosed in reference 5 as a primary light source, it is difficult from the viewpoint of space saving to be used as a primary light source, because the LED disclosed in reference 5 is much larger than an LED chip due to the size of a lens and a structure of a reflecting plate
82
. Further, such a complicated structure may cause an increase in cost.
SUMMARY OF THE INVENTION
The purpose of this invention is to provide a light source that is simple and space-saving, and has a narrow light distribution angle.
A light source unit of the present invention is characterized by a light director taking in light from a primary light source through an entrance face and outputting it, having reflection faces on both sides of the entrance face. The light director preferably has two refractive index interfaces on the way from the entrance face to the exit face, wherein the refractive index of the entrance face side is larger than that of the exit face side in the first refractive index interface and the refractive index of the exit face side is larger than that of the entrance face side in the second refractive index interface.
It is possible to arrange the angular distribution of incident light with high efficiency by reflecting the light being large in angle of incidence from the primary light source by using the reflecting surfaces, and making the reflected light enter again the first refractive index interface as making smaller its angle of incidence onto the first refractive index interface by means of the reflecting surfaces at both sides of the entrance face, and make narrow the angular distribution of emergent light with high efficiency by further making narrower the emergent
Mimura Koji
Saitoh Goroh
Sumiyoshi Ken
Yagi Yoshie
Cariaso Alan
NEC Corporation
Young & Thompson
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