Illumination – Revolving
Reexamination Certificate
2001-01-16
2003-03-18
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S026000, C362S027000, C349S065000, C349S058000, C349S150000
Reexamination Certificate
active
06533428
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flat-surface type display device having a transmissive display panel.
2. Description of Relevant Art
A conventional surface light source device used as a backlight of a flat-surface type display device having a transmissive display panel is classified into two systems depending on the position of the light source: a direct under-light system and an edge light system. In general, the direct under-light system is chiefly adopted in a large-scale display device that requires luminance, such as a monitor or an advertising tower, whereas the edge light system is chiefly adopted in a display device that requires thinness and lightness, such as a display device of a personal computer (hereinafter, abbreviated to PC). In particular, in case of notebook PCs with which the portability is of importance, the surface light source device of the edge light system is employed in almost all the products equipped with transmissive display panels.
The surface light source device of the edge light system is classified into a one-side type and a two-side type depending on the position of the linear light source. However, the basic arrangement is substantially the same in both except for the shape of a light guide plate and the total number of the linear light sources, etc.
FIG. 7
is a view showing a cross section of a conventional surface light source device of a one-light-at-one-side (one-light-at-long-side) type. In the drawing, Numeral
1
denotes a linear light source composed of a cold cathode fluorescent tube or the like; Numeral
2
denotes a reflector that is provided to surround the linear light source
1
so as to reflect light emitted from the linear light source
1
in one direction; Numeral
3
denotes a rectangular light guide plate to which the reflector
2
surrounding the linear light source
1
is attached at one edge and on which light emitted from the linear light source
1
and reflected by the reflector
2
in one direction is incident; Numeral
4
denotes a reflection sheet placed at the back surface side of the light guide plate
3
; Numeral
5
denotes an optical sheet placed at the main surface (light emitting surface) side of the light guide plate
3
; and Numeral
11
denotes reflection dots formed on the back surface of the light guide plate
3
.
The reflector
2
is made of a film of resin, such as PET, on which a metal layer or a metal reflection film is formed.
The light guide plate
3
is formed by making transparent resin, such as acrylic, into a desired shape by means of machining or injection molding, and then polishing the surface as the necessity arises. Light incident on the light guide plate
3
propagates throughout the same while repeating total reflections and reaches the opposing edge. The incident light is reflected irregularly by the reflection dots
11
formed on the back surface of the light guide plate
3
on the way to the opposing edge. Thus, a part of the light comes out from the main surface of the light guide plate
3
, and the rest is reflected again by an interface between the main surface of the light guide plate
3
and an external (air) and directed to the back surface of the light guide plate
3
. The light directed to the back surface of the light guide plate
3
is reflected by the reflection sheet
4
placed thereon. Thus, a part of the light goes into the light guide plate
3
again and comes out from the main surface of the light guide plate
3
, and the rest propagates throughout the light guide plate
3
again, repeats the same process, and comes out from the main surface of the light guide plate
3
.
The reflection dots
11
are formed on the back surface of the light guide plate
3
by means of printing using white ink having high reflectance, frosting finish, hot plating or injection molding. The density of the formed dots increases with distance from the light source, so that a uniform luminance distribution is achieved on the main surface of the light guide plate
3
by compensating a quantity of out-going light that decreases with distance from the linear light source
1
.
Generally, a white or opalescent resin film or a resin film having thereon vapor-deposited a metal thin film is used as the reflection sheet
4
.
The optical sheet
5
is formed by combining a plurality of opalescent resin films called as diffusion sheets and resin lens films (lens sheets) provided with a great many triangular prisms and thereby having a light collecting property. Typically, the optical sheet
5
has a structure, in which the lens film is sandwiched between the diffusion sheets. The optical sheet
5
increases luminance at a desired viewing angle by enhancing uniformity and directivity of light that comes out from the main surface of the light guide plate
3
.
Factors that determine the performance (luminance and uniformity thereof) of the surface light source device of the edge light system include (1) propagation efficiency of light that goes into the light guide plate
3
and propagates throughout the same, and (2) incidence efficiency of light that is emitted from the linear light source
1
and incident on the light guide plate
3
. As to the propagation efficiency throughout the light guide plate
3
, as shown in
FIG. 7
, better efficiency is achieved when the light guide plate
3
has a rectangular cross section, and light under the total reflection condition propagates while repeating total reflections unless it is reflected irregularly by the reflection dots
11
and reaches the edge opposing the linear light source
1
. Also, the incidence efficiency of light that is emitted from the linear light source
1
and incident on the light guide plate
3
depends on the thickness of a light-incident portion of the light guide plate
3
and the diameter of the linear light source
1
. As is shown in
FIG. 8
, the efficiency is improved as the thickness of the light-incident portion of the light guide plate
3
increases in comparison with the diameter of the linear light source
1
.
However, in a product employing the surface light source device of the edge light system as the backlight, because the weight, shape, etc. of the product are limited, it is impossible to design the product by giving the priority on the optical performance over the rest. More specifically, in case of a notebook PC adopting a flat-surface type display device having a transmissive liquid crystal panel, there has been an increasing need to produce a compact, light, and extremely thin display device to meet the demands of a compact, light notebook PC. Under these circumstances, with the display device that needs a liquid crystal panel and a backlight as well as an electric circuit for driving the liquid crystal panel on a signal supplied from an external device, it is becoming increasingly necessary to reduce the thickness of the product to the extent that the optical performance as the backlight will not be impaired.
FIG. 9
shows a typical conventional liquid crystal display device having a transmissive liquid crystal panel produced with an object to reduce the thickness of the product without impairing the optical performance of the backlight. In the drawing, Numeral
1
denotes a linear light source; Numeral
2
denotes a reflector; Numeral
3
denotes a light guide plate having a wedge-shaped cross section; Numeral
4
denotes a reflection sheet; Numeral
5
denotes an optical sheet; Numeral
6
denotes a transmissive display panel (liquid crystal panel, herein); Numeral
7
denotes a circuit board; Numeral
8
denotes a tape carrier package (hereinafter, abbreviated to TCP) composed of an elastic wiring board used in electrically connecting the liquid crystal panel
6
and circuit board
7
and driving ICs formed thereon; Numeral
9
denotes a mechanism component (mold frame); and Numeral
10
denotes a front frame. In the display device shown in
FIG. 9
, the thickness at the light-incident portion is secured by shaping the cross section of the light guide plate
3
Ito Atsushi
Nishida Yoshihide
Ogo Ikuo
Yachi Shigeru
Yoneda Toshiyuki
Kabushiki Kaisha Advanced Display
McDermott & Will & Emery
O'Shea Sandra
Tsidulko Mark
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