U.S. patent application number 11/636568 was filed with the patent office on 2008-02-28 for surface light source device, backlight unit and liquid crystal display having the same.
This patent application is currently assigned to LG Electronics Inc.. Invention is credited to Weon Woong Lee.
Application Number | 20080049441 11/636568 |
Document ID | / |
Family ID | 38441890 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080049441 |
Kind Code |
A1 |
Lee; Weon Woong |
February 28, 2008 |
Surface light source device, backlight unit and liquid crystal
display having the same
Abstract
The present invention is directed to a surface light source
device utilizing a light pipe. The present invention is also
directed to a backlight unit and a liquid crystal display which are
provided with such surface light source device. A surface light
source device comprises at least one light source generating light;
and at least one hollow light pipe, the light pipe includes a first
light waveguide unit with structured surface on at least one side;
and, a second light waveguide unit with structured surface on at
least one side and disposed substantially parallel to the first
light waveguide unit, wherein a longitudinal direction of the
structured surface of the first light waveguide unit and a
longitudinal direction of the structured surface of the second
light waveguide unit form a certain angle.
Inventors: |
Lee; Weon Woong; (Incheon,
KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
LG Electronics Inc.
|
Family ID: |
38441890 |
Appl. No.: |
11/636568 |
Filed: |
December 11, 2006 |
Current U.S.
Class: |
362/561 |
Current CPC
Class: |
G02B 6/0096 20130101;
G02F 1/133615 20130101; G02F 1/133604 20130101; G02B 6/0055
20130101; G02B 6/0061 20130101; G02B 6/0053 20130101 |
Class at
Publication: |
362/561 |
International
Class: |
A47F 3/00 20060101
A47F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2006 |
KR |
10-2006-0079549 |
Claims
1. A liquid crystal display comprising: a liquid crystal panel
displaying images according to electrical signals provided from the
outside device; and a backlight unit for illuminating the liquid
crystal panel from the back of the liquid crystal panel, the
backlight unit comprising: a surface light source device for
providing surface light, the surface light source device including:
at least one light source generating light; and at least one hollow
light pipe including: a first light waveguide unit with structured
surface on at least one side; and a second light waveguide unit
with structured surface on at least one side and disposed
substantially parallel to the first light waveguide unit, wherein a
longitudinal direction of the structured surface of the first light
waveguide unit and a longitudinal direction of structured surface
of the second light waveguide unit form a certain angle.
2. The liquid crystal display of claim 1, wherein the structured
surface includes an array of prisms, wherein the certain angle
formed by a longitudinal direction of the prisms of the first light
waveguide unit and a longitudinal direction of the prisms of the
second light waveguide unit is a substantially right angle.
3. A backlight unit for illuminating a liquid crystal panel from
the back of the liquid crystal panel, the backlight unit comprising
a surface light source device for providing surface light, the
surface light source device including: at least one light source
generating light; and at least one hollow light pipe including: a
first light waveguide unit with structured surface on at least one
side; and a second light waveguide unit with structured surface on
at least one side and disposed substantially parallel to the first
light waveguide unit, wherein a longitudinal direction of the
structured surface of the first light waveguide unit and a
longitudinal direction of the structured surface of the second
light waveguide unit form a certain angle.
4. The backlight unit of claim 3, further comprising at least one
optical sheet disposed in one side of the surface light source
device, wherein the optical sheet receives the light emitted from
the surface light source device and provides the light to the
liquid crystal panel.
5. The backlight unit of claim 3,wherein the structured surface
includes an array of prisms
6. The backlight unit of claim 3, wherein the at least one light
source is LEDs, and wherein the surface light source further
comprises: a printed circuit board electrically connecting a
electric power source to the LEDs, wherein the LEDs are mounted on
the printed circuit board; and a housing receiving and supporting
the printed circuit board.
7. The backlight unit of claim 3, further comprising a reflective
sheet disposed under the light pipe to reflect the light emitted
through a bottom surface of the light pipe and re-input the light
into the inside of the light pipe.
8. The backlight unit of claim 3, wherein the light source is CCFLs
or EEFLs disposed inside or along at least one side of the light
pipe.
9. The backlight unit of claim 3, further comprising a diffusive
layer disposed on the outer surface of the light pipe to receive at
least the light emitted from the light emitting surface, the
diffusive layer including: a base material consisting of a
light-transmissive resin; and a plurality of diffusion particles
distributed in the base material.
10. The backlight unit of claim 9, wherein the diffusion particles
are beads.
11. The backlight unit of claim 9, further comprising a reflector
having a surface capable of reflecting light, wherein the reflector
is disposed inside the light pipe.
12. The backlight unit of claim 9, further comprising a reflector
having a surface capable of reflecting light, wherein the reflector
is disposed outside the light pipe.
13. The backlight unit of claim 5, wherein the certain angle formed
by a longitudinal direction of the prisms of the first light
waveguide unit and a longitudinal direction of the prisms of the
second light waveguide unit is a substantially right angle.
14. The backlight unit of claim 5, wherein the prisms of the first
waveguide unit are enlarged as the distance from the light source
is farther.
15. A surface light source device for providing surface light,
comprising: at least one light source generating light; and at
least one hollow light pipe including: a first light waveguide unit
with structured surface on at least one side; and a second light
waveguide unit with structured surface on at least one side and
disposed substantially parallel to the first light waveguide unit,
wherein a longitudinal direction of the structured surface of the
first light waveguide unit and a longitudinal direction of the
structured surface of the second light waveguide unit form a
certain angle.
16. The surface light source device of claim 15 wherein the
structured surface includes an array of prisms.
17. The surface light source device of claim 15, wherein the at
least one light source is LEDs, and wherein the surface light
source further comprises: a printed circuit board electrically
connecting a electric power source to the LEDs, wherein the LEDs
are mounted on the printed circuit board; and a housing receiving
and supporting the printed circuit board.
18. The surface light source device of claim 15, wherein the light
source is CCFLs or EEFLs disposed inside or along at least one side
of the light pipe.
19. The surface light source device of claim 15, further comprising
a diffusive layer disposed on the outer surface of the light pipe
to receive at least the light emitted from the light emitting
surface, the diffusive layer including: a base material consisting
of a light-transmissive resin; and a plurality of diffusion
particles distributed in the base material.
20. The surface light source device of claim 16, wherein the
certain angle formed by a longitudinal direction of the prisms of
the first light waveguide unit and a longitudinal direction of the
prisms of the second light waveguide unit is a substantially right
angle.
21. The surface light source device of claim 16, wherein the prisms
of the first waveguide unit are enlarged as the distance from the
light source is farther.
Description
CROSS-REFERENCE TO A RELATED APPLICACTION
[0001] The present application claims the benefit of priority under
35 U.S.C. 119 based on the Korean patent application number
10-2006-0079549 filed on Aug. 22, 2006. This application is
incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention is directed to a surface light source
device utilizing a light pipe. The present invention is also
directed to a backlight unit and a liquid crystal display which are
provided with such surface light source device.
[0004] 2. Background
[0005] The liquid crystal display, also know as LCD, is an
electronic device that transforms electrical signals into visual
signals by utilizing the change in the transmittance of the liquid
crystals according to applied voltages.
[0006] As well known in the art, the liquid crystal display is a
non-emitting display device. Therefore, the liquid crystal display
needs to use an outside light source unit for illuminating the
viewing plane of the liquid crystal panel from its outside in order
to display visual information. A backlight unit is conventionally
used for this use.
[0007] FIG. 1 is a perspective view illustrating a liquid crystal
display.
[0008] Referring to FIG. 1, the liquid crystal display 30 comprises
a liquid crystal panel 20 and a backlight unit 10 disposed at the
back of the liquid crystal panel. The liquid crystal panel 20
receives the light provided by the backlight unit 10 to display
images.
[0009] In general, the backlight unit 10 comprises a light source
unit 12, a light guide plate 14, a reflective sheet 16 and optical
sheets 18.
[0010] The light source unit 12 comprises a light source 12a and a
light source reflector 12b. A cold cathode fluorescent lamp (CCFL)
or an external electrode fluorescent lamp (EEFL) may be used for
the light source 12a. The light source 12a is received inside the
light source reflector 12b and disposed along one surface of the
light guide plate 14. The light source reflector 12b is disposed
outside the light source 12a to reflect the light generated at the
light source 12a such that the light is inputted into the light
guide plate 14.
[0011] The side surface of the light guide plate 14 disposed
adjacent to the light source unit 12 becomes a light incidence
surface for receiving the light. The light generated at the light
source unit 12 is inputted into the light guide plate 14 through
the light incidence surface, and emitted through the upper surface
of the light guide plate 14. The upper surface of the light guide
plate 14 becomes the light emitting surface for emitting the
light.
[0012] The reflective sheet 16 reflects the light emitted through
the lower surface of the light guide plate 14 such that the light
is re-inputted into the inside of the light guide plate 14, which
improves the light efficiency of the backlight unit 10.
[0013] The optical sheets 18 may comprise a diffuser sheet 18a, a
prism sheet 18b and a protector sheet 18c. The optical sheets 18a,
18b and 18c control the light such that the light is effectively
provided to the viewing plane of the liquid crystal panel 20.
[0014] However, the edge-light type backlight unit 10, which only
uses the light that is inputted through the side surfaces of the
light guide plate for illumination, has a problem that the light
generated at the light source 12 is not fully used for illumination
because the light loss occurs considerably at the light guide plate
14.
[0015] Furthermore, the direct type backlight unit, which has a
plurality of light sources positioned directly under the liquid
crystal panel, also has a problem that the light loss occurs at
optical plates such as a diffusion plate. In addition, the light
sources arranged adjacent to each other generates heat convection
inside the backlight unit, and such heat convection deforms the
optical sheets disposed over the light sources. The deformation of
the optical sheets deteriorates the display quality.
[0016] To solve such problems, there have been recently various
attempts to develop a surface light source device which emits light
in the form of surface light. Information relevant to attempts to
address the above problems can be found in U.S. Pat. Nos. 6,771,330
and 6,514,113 and U.S. patent application No. 2004-004757, which
disclose the surface light source utilizing a flat fluorescent lamp
(FEL), LEDs or carbon nano tubes (CNTs). However, the surface light
source devices of the above publications still suffer from one or
more of the following disadvantages: the complex manufacturing
process, unsatisfactory optical property, and high power
consumption.
[0017] For the foregoing reasons, there is a need for a surface
light source device that can be easily manufactured, that has
satisfactory optical properties and that consumes low electric
power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other features, aspects and advantages of the
present invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
where:
[0019] FIG. 1 is a perspective view illustrating a liquid crystal
display;
[0020] FIG. 2a is an exploded perspective view illustrating a
liquid crystal display according to one embodiment of the present
invention;
[0021] FIG. 2b is a cross-sectional view illustrating the liquid
crystal display of FIG. 2a;
[0022] FIG. 2c is a cross-sectional view illustrating the liquid
crystal display according to another embodiment;
[0023] FIG. 2d is a cross-sectional view illustrating the light
pipe of FIG. 2c taken along the line A-A;
[0024] FIG. 2e is a cross-sectional view illustrating a part of the
liquid crystal display according to another embodiment of the
present invention;
[0025] FIG. 2f is a cross-sectional view illustrating a part of the
liquid crystal display according to further another embodiment of
the present invention;
[0026] FIG. 3a is an exploded perspective view illustrating a
surface light source device according to one embodiment of the
present invention;
[0027] FIG. 3b is a view illustrating a structure of the prisms of
the light pipe of FIG. 3a;
[0028] FIG. 4a is a cross-sectional view of the liquid crystal
display according to further another embodiment of the present
invention;
[0029] FIG. 4b is a cross-sectional view of the surface light
source of FIG. 4a taken along the line B-B;
[0030] FIGS. 4c and 4d are enlarged partial cross-sectional views
of the area E of FIG. 4b;
[0031] FIGS. 5a to 5c are cross-sectional views illustrating other
embodiments of the diffusive layer and the reflector of FIG.
4b;
[0032] FIG. 6 is an exploded perspective view illustrating a
surface light source device according to another embodiment of the
present invention;
[0033] FIGS. 7a and 7b are cross-sectional views illustrating a
surface light source device according to further another embodiment
of the present invention; and
[0034] FIGS. 8a and 8b are cross-sectional views illustrating the
surface light source device according to further another embodiment
of the present invention.
DETAILED DESCRIPTON OF THE INVENTION
[0035] An object of the present invention is to provide a surface
light source device that can be easily manufactured.
[0036] Another object of the present invention is to provide a
surface light source device that consumes low electric power and
that is free of the heat-related problems.
[0037] Further another object of the present invention is to
provide a surface light source device that is easily applicable to
large size and thin display devices.
[0038] Still further another object of the present invention is to
provide a backlight unit and a liquid crystal display that are
provided with such surface light source device.
[0039] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
[0040] In the following drawings, the same reference numbers will
be used to refer to the same or like parts through all embodiments.
In addition, the detailed descriptions of the identical parts are
not repeated.
[0041] FIG. 2a is an exploded perspective view illustrating a
liquid crystal display according to one embodiment of the present
invention; and FIG. 2b is a cross-sectional view illustrating the
liquid crystal display of FIG. 2a.
[0042] Referring to FIGS. 2a and 2b, a liquid crystal display 300
of the present invention comprises a liquid crystal panel 200 and a
backlight unit 100A.
[0043] The liquid crystal display 300 displays images according to
driving signals and data signals provided by an outside device. To
understand and work the present invention, it is not important to
describe the detailed structure of the liquid crystal panel 200.
And, the idea of the present invention is widely applicable to any
type of liquid crystal panel usually employed in the liquid crystal
display. Therefore, the structure of the liquid crystal panel 200
will not need to be herein described.
[0044] The backlight unit 100A is positioned at the back of the
liquid crystal panel 200 to provide light, for example white light
to the liquid crystal panel 200. The backlight unit 100A comprises
a surface light source device 110A for providing surface light
suited to illuminating the viewing plane of the liquid crystal
panel 200. Selectively, the backlight unit 100A may include optical
sheets 180 that are disposed between the liquid crystal panel 200
and the surface light source device 110A to transform the light
provided by the surface light source device 110A to more suitable
light for illuminating the liquid crystal panel 200.
[0045] The surface light source device 110A according to one
embodiment comprises light source unit 120, a light pipe 140 and a
reflective sheet 160.
[0046] Each light source unit 120 comprises light sources 120a
generating the light. The light sources 120a according to one
embodiment are point light sources such as light emitting diodes
(LEDs). In this case, the light sources 120a are mounted on a
printed circuit board (PCB) 120b in a certain arrangement, and the
outside electric power source is electrically connected to the
light sources 120a through the wiring patterns of the PCB 120b.
[0047] According to one embodiment, the light sources 120a are
disposed along two side surfaces. Therefore, the light generated at
the light sources 120a is inputted into the light pipe 140 through
its side surfaces. Each light source unit 120 comprises a housing
120c for receiving and supporting the PCB 120b mounted with the
light sources 120a. The housing 120c may be made of metal and
plastic materials, and each housing 120c has an inside groove for
the PCB 120b to be inserted therein. Preferably, the inner wall of
the housing 120c has a reflective coating to reflect the light
emitted from the light sources 120a.
[0048] The two side surfaces of the light pipe 140 become light
incidence surfaces through which the light generated at the light
source unit 120 is inputted into the light pipe 140, and the upper
surface of the light pipe 140 becomes the light emitting surface
through which the light is outputted from the light pipe 140. The
light inputted through the light incident surfaces progresses
through inside of the light pipe 140 by total reflection, and is
outputted toward the liquid crystal panel 200 direction through the
light emitting surface. The light emitting surface is preferably at
least as wide as or wider than the viewing plane of the liquid
crystal panel 200 so that the light is uniformly provided to the
viewing plane.
[0049] Although the light source unit 120 is disposed at the side
area of the light pipe 140, the backlight unit 100A has almost
equal light efficiency to the conventional direct-lighting type
backlight unit because the light pipe 140 has excellent light
transportation capability and little light loss therein.
Additionally, for the same level of brightness, fewer LEDs can be
used in the backlight unit 100A of the present invention than in
the conventional direct-lighting type backlight unit.
[0050] According to another embodiment, the light source unit 120
may be disposed only at one side area of the light pipe 140. In
such case, the light efficiency may be secured by installing
reflecting means at the opposite side area of the light pipe 140 to
reflect and reuses the light transported to the end of the light
pipe 140. Preferably, the light pipe 140 is designed to obtain
uniform emitting light in such a manner that the cross-sectional
area of the light pipe 140 becomes smaller along the longitudinal
direction.
[0051] FIG. 2c is a cross-sectional view illustrating the liquid
crystal display according to another embodiment.
[0052] Referring to FIG. 2c, a light source 220 of a liquid crystal
display 300 is a linear light source. The light source may be, for
example, a CCFL or an EEFL.
[0053] FIG. 2d is a cross-sectional view illustrating the light
pipe of FIG. 2c taken along the line A-A.
[0054] Referring to FIG. 2d, the inside of the light pipe 140 is
hollow and filled with air, and the cross-section of the light pipe
140 may be oval or rectangular. The light pipe 140 may be a kind of
hollow light waveguide. The light pipe 140 has a suitable structure
for transporting the light inputted through its one or both sides
in the longitudinal direction.
[0055] According to one embodiment, the inner surface 140b of the
light pipe 140 is structured with prisms arranged in micro pitches,
wherein each prism is extended in the longitudinal direction.
[0056] Here, as shown in FIG. 2c, the inner surface 140b is
structured with prisms. Only, in FIG. 2d, a cut side of the prisms
of the inner surface 140b is shown, and so the inner surface 140b
is described as a straight line.
[0057] The outer surface of the light pipe 140 is not structured
but smooth, and a part of the outer surface 140a becomes the light
emitting surface for emitting the light to the liquid crystal panel
200.
[0058] Alternatively, the outer surface 140a of the light pipe 140
may be structured, and the inner surface 140b of the light pipe 140
may be smooth.
[0059] Alternatively, both the outer and inner surfaces 140a and
140b of the light pipe 140 may be structured.
[0060] The distance between the outer surface 140a and the inner
surface 140b varies widely according to the application
circumstance. However, considering the light loss, it is preferable
that the distance has a value of between about 50 .mu.m and about
300 .mu.m.
[0061] The light pipe 140 may be made of a thermoplastic resin that
has good light transmittance, mechanical strength (especially
impact resistance), thermal resistance and electrical stability.
Preferably, the light pipe 140 is made of polyethylen terephthalate
(PET), polycarbonate (PC) or polymethyl methacrylate (PMMA). More
preferably, the light pipe 140 is made of polymethyl methacrylate
(PMMA).
[0062] Referring back to FIGS. 2a to 2c, the surface light source
device 110A according to one embodiment comprises a reflective
sheet 160. The reflective sheet 160 reflects the light output
through the lower surface of the light pipe 140 to re-input the
light into the light pipe 140, thereby the light efficiency may be
improved.
[0063] The reflector sheet 160 may be manufactured by applying Ag
on a sheet made of SUS, Brass, Al, PET, etc and coating it with Ti
to prevent the thermal deterioration caused by heat absorption.
[0064] Alternatively, the reflective sheet 160 may be obtained by
dispersing micro-pores capable of scattering the light in a resin
sheet such as PET.
[0065] Selectively, the backlight unit 100A may include a set of
optical sheets 180 disposed between the surface light source device
110A and the liquid crystal panel 200. The set of optical sheets
180 may comprise a diffuser sheet 180a, a prism sheet 180b and a
protector sheet 180c.
[0066] The light emitted through the light emitting surface is
inputted into the diffuser sheet 180a. The diffuser sheet 180a
scatters the light to make the brightness uniform and widen the
viewing angle.
[0067] Because the brightness declines sharply while the light
passes through the diffuser sheet 180a, the prism sheet 180b is
provided in the backlight unit 100A to compensate such declination
of brightness. The prism sheet 180b refracts the light emitted from
the diffuser sheet 180a in a low angle to collimate the light
toward the front direction; thereby the brightness is improved
within the effective viewing angle.
[0068] The protector sheet 180c is disposed over the prism sheet
180b. The protector sheet 180c prevents the surface of the prism
sheet 180b from being damaged, and also re-widens the viewing angle
once narrowed by the prism sheet 180b.
[0069] The specified structure and materialistic property of the
optical sheets 180 are not important to understand and work the
present invention, and any conventional structure and material
normally used in the art are widely applicable to the optical sheet
180 of the present invention.
[0070] Hereinafter, other embodiments of the present invention will
be described.
[0071] FIG. 2e is a cross-sectional view illustrating a part of the
liquid crystal display according to another embodiment of the
present invention. FIG. 2f is a cross-sectional view illustrating a
part of the liquid crystal display according to further another
embodiment of the present invention. For the convenience, the same
parts as those of the foregoing embodiment are not illustrated.
[0072] In the foregoing embodiment, LEDs in the form of point light
sources are employed for the lights sources 120a. However, the
linear light sources such as CCFLs or EEFLs may be employed for the
light sources 120a. In such case, as shown in FIG. 2e, the linear
light sources 130 are disposed adjacent to each other inside the
light pipe 140.
[0073] Here, since the surface light source device 110A according
to one embodiment has a structure where the light sources 130
generating heat may be received inside the light pipe 140, the heat
generated at the light sources 130 is circulated only inside the
light pipe 140 and the heat is prevented from being easily
transferred to the optical sheets 180. Therefore, the heat-related
deformation of the optical sheets 180 may be prevented.
[0074] Additionally, in the foregoing embodiment, the surface light
source device 110A is embodied with one light pipe 140. However, as
shown in FIG. 2f, the surface light source device 110A may be also
embodied with a plurality of light pipes 140 disposed in such a
manner that the adjacent light pipes 140 contact each other. Such
simple disposition of the light pipes 140 allows the optical
communication between the light pipes 140 because each light pipe
140 has the same dimension.
[0075] This allows the application of the surface light source of
the present invention to the large size display. Namely, simply
arranging the light pipes 140 vertically and horizontally according
to the size of the liquid crystal panel and installing the light
source units using the point light source (120 of FIG. 2b) and the
linear light source (220 of FIG. 2c) at the side areas of the light
pipe 140, inserting the linear light sources (130 of FIG. 2e) can
embody large size surface light source device.
[0076] FIG. 3a is an exploded perspective view illustrating the
surface light source device according to one embodiment of the
present invention. And, FIG. 3b is a view illustrating the
structure of prisms of the light pipe of FIG. 3a.
[0077] Referring to FIGS. 3a and 3b, the surface light source
device 340 according to one embodiment comprises a light source 220
and a light pipe. The light pipe comprises a plurality of light
waveguide units 342, 344, 346 and 348. Each of the light waveguide
units 342, 344, 346 and 348 has a surface of which at least one
side is structured.
[0078] Hereinafter, such a constitution that the structured surface
includes an array of prisms will be described, but the present
invention is not limited thereto, and the surface may be structured
in various shapes.
[0079] The inner surface of the first light waveguide unit 342 of
the light pipe is structured with a plurality of prisms, and the
first light waveguide unit 342 has a surface through which a light
from the light source 220 is incident.
[0080] The second light waveguide unit 344 is disposed
substantially parallel to the first light waveguide unit 342, and
its one surface is structured with a plurality of prisms. Also, the
second light waveguide unit 344 has a surface through which a light
is emitted into the liquid panel 200 direction.
[0081] Here, the longitudinal direction L.sub.1 of the prisms of
the first light waveguide unit 342 and the longitudinal direction
L.sub.2 of the prisms of the second light waveguide unit 344 form a
certain angle .alpha.. According to one embodiment, the certain
angle .alpha. may be a right angle.
[0082] Also, the longitudinal direction of the prisms of the third
light waveguide unit 346 and the longitudinal direction of the
prisms of the forth light waveguide unit 348 may form a certain
angle.
[0083] The light pipe of the present invention may be molded by
already known plastic molding process such as injection molding or
extrusion molding. It is within the capability of a person skilled
in the art to make the light pipe by such already known molding
processes with the above mentioned materials without detailed
description.
[0084] FIG. 4a is a cross-sectional view of the liquid crystal
display according to further another embodiment of the present
invention; FIG. 4b is a cross-sectional view of the surface light
source of FIG. 4a taken along the line B-B; and FIGS. 4c and 4d are
enlarged partial cross-sectional views of the area E of FIG.
4b.
[0085] Referring to FIGS. 4a and 4b, the liquid crystal display 400
comprises the liquid crystal panel 200 and a backlight unit
100B.
[0086] The backlight unit 100B comprises a surface light source
device 110B for providing surface light. The backlight unit 100B
may optionally include the optical sheets 180 to transform the
light provided by the surface light source device 110B to more
suitable light for the illumination of the panel 200.
[0087] The surface light source device 110B comprises the light
source units 120, the light pipe 140, a diffusive layer 142
disposed outside the light pipe and a reflector 144 disposed inside
the light pipe 140.
[0088] The diffusive layer 142 enables the light confined inside
the light pipe 140 to be emitted outside the light pipe 140 and
scatters the light for brightness uniformity.
[0089] Referring to FIGS. 4c and 4d, the diffusive layer 142
comprises a base material 142b consisting of a resin and a
plurality of diffusion particles 142a and 142a' distributed in the
base material 142b.
[0090] The base material 142b is preferably an acrylic resin that
has good light transmittance, thermal resistance and mechanical
strength. More preferably, the bases material 142b is polyacrylate
or polymethyl methacrylate.
[0091] Beads consisting of the same or other resins as the base
material 142b may be used for the diffusion particles 142a and
142a'. The diffusion particles 142a and 142a' are preferably
contained by about 25 wt % to 35 wt % against the base material
142b. More preferably, the diffusion particles 142a and 142a' are
contained by 30 wt % against the base material 142b.
[0092] According to one embodiment, the size and the distribution
of the diffusion particles 142a are random. Such random structure
increases the haze effect to prevent the defects such as scratches
that physical contacts would make on the base material 142b from
being projected onto the liquid crystal panel (200 of FIG. 4a).
[0093] According to another embodiment, the size and the
distribution of the diffusion particle 142a' are substantially
uniform. Such uniform structure allows the brightness to increase
although the haze effect rather decreases. In general, as the
uniformity of the diffusion particles 142a' increases, the haze
effect decreases but the brightness increases.
[0094] The diffusive layer 142 can be formed by various methods
already known in the art. For example, the diffusive layer 142 can
be obtained by a method where diffusion particles such as beads are
mixed with a liquid phase resin and the mixture is applied to a
base film, followed by the mixture being cured; and the film is
thermo-compressed onto the outside surface of the light pipe 140.
Alternatively, the diffusive layer 142 can be obtained by another
method where a liquid phase resin with bead distributed therein is
applied to the outside surface of the light pipe 140.
[0095] Referring back to FIGS. 4a and 4b, the reflector 144 is
disposed inside the light pipe 140. The reflector 144 prevents the
light from being emitted through the lower surface of the light
pipe 140 and thus improves the light efficiency. Furthermore, the
reflector 144 enables the light confined in the light pipe 140 to
be emitted outside the light pipe 140.
[0096] The reflector 144 may consist of high reflective materias.
For example, the reflector 144 comprises a reflective coating
consisting of metals such as Al or Ag.
[0097] The optical sheets 180 may optionally be disposed between
the liquid crystal panel 200 and the surface light source device
110B, and the optical sheets 180 may comprise the diffuser sheet
180a, the prism sheet 180b and the protector sheet 180c.
[0098] In the foregoing embodiment, the diffusive layer 142 fully
covers the outer surface of the light pipe 140, and the reflector
144 is inserted in the light pipe 140. However, the structure and
disposition of the diffusive layer 142 and the reflector 144 can be
modified variously by a person skilled in the art. Hereinafter,
some modifications of the diffusive layer 142 and the reflector 144
will be described with reference to the drawings.
[0099] FIGS. 5a to 5c are cross-sectional views illustrating other
embodiments of the diffusive layer and the reflector of FIG. 4b.
Only, the structural differences from the diffusive layer 142 and
the reflector 144 are mainly described for convenience.
[0100] Referring to FIG. 5a, according to another embodiment, the
diffusive layer 142 is disposed to fully cover the outer surface of
the light pipe 140, and the reflector 244 is disposed on the lower
surface of the diffusive layer 142 as shown in the drawing.
[0101] Referring to FIG. 5b, according to further another
embodiment, the diffusive layer 342 and the reflector 344 both are
disposed only on a certain area of the outer surface of the light
pipe 140. Here, the diffusive layer 342 is formed at the position
facing the liquid crystal panel (not shown), and the reflector 344
is disposed on the lower surface of the light pipe 140 and faces
the diffusive layer 342 with the light pipe 140 therebetween.
[0102] Referring to FIG. 5c, according to still further another
embodiment, the diffusive layer 442 is formed to fully cover the
outer surface of the light pipe 440, and the reflector 444 is
disposed in the light pipe 440. Only, in this case, the inside area
of the light pipe 140 where the reflector 444 is disposed is free
of the prism structure.
[0103] FIG. 6 is an exploded perspective view illustrating the
surface light source device according to another embodiment of the
present invention.
[0104] Referring to FIG. 6, the surface light source device 640
comprises a light source 220 and a light pipe. The inner surface
642a of the first light waveguide unit 642 of the light pipe is
structured with a plurality of prisms.
[0105] The outer surface 644a of the second light waveguide unit
644 is smooth plane, and the inner surface 644b is structured with
a plurality of prisms.
[0106] Here, the longitudinal direction of the prisms of the first
light waveguide unit 642 and the longitudinal direction of the
prisms of the second light waveguide unit 644 form a certain angle.
Accordingly, the brightness of the emitting light from the light
pipe to the liquid panel 200 direction can be enhanced.
[0107] The third light waveguide unit 346a and the forth light
waveguide unit 348a are combined with both sides of the first light
waveguide unit 642 and the second light waveguide unit 644.
[0108] Each one surface of the third light waveguide unit 346a and
the forth light waveguide unit 348b is structured with a plurality
of prisms, and the longitudinal directions of the prisms form a
certain angle.
[0109] FIGS. 7a and 7b are cross-sectional views illustrating the
surface light source device according to further another embodiment
of the present invention.
[0110] Referring to FIGS. 7a and 7b, the surface light source
devices 740 and 760 comprise a light source 220 and a light pipe,
and the inner surfaces 742a and 762a of the first light waveguide
units 742 and 762 of the light pipes are structured with a
plurality of prisms.
[0111] The inner surfaces 744b and 764b of the second light
waveguides unit 744 and 764 are smooth planes, and the outer
surfaces 744a and 764a are structured with a plurality of
prisms.
[0112] Here, the longitudinal directions of the prisms of the first
light waveguide units 742 and 762 and the longitudinal directions
of the prisms of the second light waveguide units 744 and 764 form
a certain angle.
[0113] The third light waveguide units 346b and 346c and the forth
light waveguide units 348b and 348c are combined with both sides of
the first light waveguide units 742 and 762 and the second light
waveguide units 744 and 764, respectively.
[0114] FIGS. 8a and 8b are cross-sectional views illustrating the
surface light source device according to further another embodiment
of the present invention.
[0115] Referring to FIGS. 8a and 8b, the surface light source
device 840 and 860 comprises a light source 220 and a light pipe.
The inner surface 842a and 862a of the first light waveguide unit
842 and 862 of the light pipe is structured with a plurality of
prisms.
[0116] The inner surface 844b and 864b of the second light
waveguide unit 844 and 864 is smooth plane, and the outer surface
844a and 864a is structured with a plurality of prisms.
[0117] The longitudinal direction of the prisms of the first light
waveguide unit 842 and 862 forms a certain angle with the
longitudinal direction of the prisms of the second light waveguide
unit 844 and 864.
[0118] In FIG. 8a, the structured prisms of the inner surface 842a
of the first light waveguide unit 842 become larger toward the
center from the edge.
[0119] If the prisms of the inner surface 842a of the first light
waveguide unit 842 are structured as shown in FIG. 8a, though a
light is inputted through both sides, the brightness of the light
emitted through the second light waveguide unit 844 may be
controlled to be uniform.
[0120] In FIG. 8b, the light source 220 is disposed at one side
area of the light pipe. In the case, the structured prisms of the
inner surface 862a of the first light waveguide unit 862 become
larger from one edge of the light pipe adjacent to the light source
220 toward the other edge. Therefore, the brightness of the light
emitted through the second light waveguide unit 864 may be
controlled to be uniform.
[0121] Any reference in this specification to "one embodiment," "an
embodiment," "example embodiment," etc., means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
invention. The appearances of such phrases in various places in the
specification are not necessarily all referring to the same
embodiment. Further, when a particular feature, structure, or
characteristic is described in connection with any embodiment, it
is submitted that it is within the purview of one skilled in the
art to effect such feature, structure, or characteristic in
connection with other ones of the embodiments.
[0122] Although embodiments have been described with reference to a
number of illustrative embodiments thereof, it should be understood
that numerous other modifications and embodiments can be devised by
those skilled in the art that will fall within the spirit and scope
of the principles of this disclosure. More particularly, various
variations and modifications are possible in the component parts
and/or arrangements of the subject combination arrangement within
the scope of the disclosure, the drawings and the appended claims.
In addition to variations and modifications in the component parts
and/or arrangements, alternative uses will also be apparent to
those skilled in the art.
* * * * *