WO2009135337A1

WO2009135337A1 - Backlight module

Info

Publication number: WO2009135337A1
Application number: PCT/CN2008/000916
Authority: WO
Inventors: Changsheng Chu; Yutang Li
Original assignee: Industrial Technology Research Institute
Priority date: 2008-05-09
Filing date: 2008-05-09
Publication date: 2009-11-12

Abstract

A backlight module includes a base (100), a light source (200), a light-guide mask (300) and a diffusing plate (400). A light source and a light-guide mask are disposed on the base, and the light-guide mask covers on the light source. The light-guide mask has a light-diffusing portion for diffusing light rays from the light source and incident to the light-guide mask. Moreover, the light rays passing the light-guide mask are mixed in mixing space between the diffusing plate and the light-guide mask, and then diffused uniformly by the diffusing plate.

Description

BACKLIGHT MODULE

BACKGROUND OF THE INVENTION Field of Invention

The present disclosure relates to a backlight module, and more particularly to a direct-type backlight module. Related Art

A backlight modules may be classified into two types, namely, side-type backlight modules and direct-type backlight modules according to the position of the light sources arranged in the illumination modules (e.g. LCD, commercial light box, or illumination lamps, etc.). In a side-type backlight module, the light sources are disposed at side boards of the the illumination modules.

The light rays emitted by the light sources are incident to a light-guide plate from side edges of the light-guide plate, and then converted into an area light by the light-guide plate. The light rays are then irradiated by the use of a diffusing plate, a reflective layer, or the like above the light-guide plate. Comparatively, in a direct-type backlight module, the light rays are directly irradiated and mixed into an area light by a reflective layer and a diffusing plate.

Relevant techniques have been disclosed in US Patent No. 6,654,088 B2 and US Application No. US2007/0l47,035 Al.

In the direct-type backlight module, after being mixed in the area between the light source and the diffusing plate, the light rays are diffused to a planar light by the diffusing plate. However, due to the light-emitting characteristics of the light source (e.g., non-directional light source and directional light source), uneven light distribution (e.g., mura, bright and dark belts, etc. ) frequently induced after the planar light mixed and then diffused by the diffusing plate.

SUMMARY OF THE INVENTION

The present disclosure provides a backlight module, which includes a base, at least a light source, at least a light-guide mask, and a diffusing plate.

The base has a base plate and a side wall. The light source is located above the base plate, for emitting light rays. The light-guide mask is disposed on the base plate and covers the light source, and has at least a light-diffusing portion for diffusing the light rays. The diffusing plate is disposed on a side of the light-guide mask opposite to the light source to have a light-mixing space between the diffusing plate and the light-guide mask. The light rays from the light-guide mask mixed in the light-mixing space are incident to the diffusing plate and diffused by the diffusing plate.

The backlight module according to the present disclosure further comprises a reflective layer disposed on the base and the side wall.

The light-diffusing portion covers the whole of the light-guide mask. The light-diffusing portion has a plurality of light-diffusing structures. The density of the light diffusing structures at the area of the light-guide mask with higher light intensity of the light rays is higher than the density of the light diffusing structures at the area of the light-guide mask with lower light intensity of the light rays .

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: FIG. 1 is a schematic view of a backlight module according to a first embodiment of the present disclosure;

FIG. 2 is a schematic view of a backlight module according to a second embodiment of the present disclosure;

FIG. 3 is a schematic view of a backlight module according to a third embodiment of the present disclosure;

FIG. 4A is a schematic view of a conventional direct-type backlight module; FIG. 4B is a schematic view of another conventional direct-type backlight module; FIG. 4C is a schematic view of an application of a backlight module according to the present disclosure; FIG. 5 is a schematic view of uniformity measurement of luminous flux of 9 points defined by conventional backlight module;

FIG. 6 A shows an ASAP simulation result taken at a mixing height of 2 cm of the backlight module shown in FIG. 4A;

FIG. 6B shows an ASAP simulation result taken at a mixing height of 2 cm of the backlight module shown in FIG 4B;

FIG. 6C shows an ASAP simulation result taken at a mixing height of 2 cm of the backlight module shown in FIG. 4C;

FIG. 7A is a schematic view of yet another conventional direct-type backlight module; FIG. 7B is a schematic view of another application of a backlight module according to the present disclosure;

FIG 8 A shows an ASAP simulation result taken at a mixing height of 2 cm of the backlight module shown in FIG. 7 A; and

FIG. 8B shows an ASAP simulation result taken at a mixing height of 2 cm of the backlight module shown in FIG. 7B.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of a backlight module according to a first embodiment of the present disclosure. Referring to FIG. 1, in this embodiment, a backlight module 10 includes a base 100, at least a light source 200, at least a light-guide mask 300, and a diffusing plate 400. As shown in FIG. 1 , the backlight module 10 is a direct-type backlight module.

The base 100 has a base plate 110 and a side wall 120. As shown in FIG. 1, there are two side walls 120 adjacent to the base plate 110. In other words, the side wall 120 is connected to side edges of the base plate 110. The side wall 120 and the base plate 110 create an angle 130. The angle 130 ranges from 90 degrees to 170 degrees. The material of the base 100 can be selected from reflective materials like metal, Al or Al-Mg alloy, or a material that is easy to be processed and shaped such as plastic.

The light sources 200 are located above the base plate 110, for emitting the light rays. The light sources 200 are non-directional light sources, such as cold cathode fluorescent lamps

(CCFLs) and hot cathode fluorescent lamps (HCFLs). The light emitting characteristic of the non-directional light source refers to that the light rays emitted from every point on the light-emitting surface of the light sources 200 have the similar light intensity to each other.

The light-guide mask 300 is disposed on the base plate 110 and covers the light sources 200. In other words, the light-guide mask 300 covers the base plate 110, such that the light sources 200 are sandwiched between the light-guide mask 300 and the base plate 110. The light-guide mask 300 is made of a transparent material, such as PolyMethyl MethAcrylate (PMMA) or Poly Carbonate (PC). The light-guide mask 300 has light-transmissive and light-diffusing optical characteristics. The light-guide mask 300 may be manufactured by injection molding or pressure casting. When a plurality of light-guide masks 300 are used, the light-guide masks 300 can be manufactured separately as a single structure to cover at least one of the light sources 200. The light-guide mask 300 can be integrally manufactured to be one piece element to cover the plurality of light sources 200.

The shape of the light-guide mask 300 varies according to different characteristics of the light sources 200. Please referring to FIG. 1, in this embodiment, the light sources 200 are non-directional light sources such as CCFLs. The inner surface 301 of the light-guide mask 300 corresponding to the CCFL is a curved surface which corresponds to the shape of the light-emitting surface of the CCFL. Thus, when the light rays emitted by the CCFL are incident to the inner side 301, each light ray is incident to the inner side 301 in a substantially perpendicular way. The outer surface 302 of the light-guide mask 300 can be a shape of corner column, a curved surface or other geometrical surfaces.

The light-guide mask 300 includes at least a light-diffusing portion 310. The location of the light-diffusing portion 310 varies according to different characteristics of the light sources 200. In the embodiment of FIG. 1, the light-diffusing portion 310 is located on an area of the light-guide mask 300 having a higher light intensity of light rays incident into the light-guide mask 300. Consequently, the light rays with higher light intensity incident into the light-diffusing portion 310 are diffused and then pass through the light-diffusing portion 310. The light rays with lower intensity incident into the area other than the light-diffusing portion 310 pass through the light-guide mask 300. Therefore, the light rays passing through the light-guide mask 300 are preliminary uniformized.

In this embodiment of FIG. 1, the light-guide mask 300 covers on a plurality of non-directional light sources 200 (CCFLs in this embodiment). The area between two light sources 200 receives more light rays than that received by the area corresponding to top of the light sources 200. Consequently, the light-diffusing portion 310 is located at the area other than the area corresponding to top of the light sources 200 to reduce the light rays directly passing through the light-diffusing portion.

The light-diffusing portion 310 may be formed by forming inkjet mesh points or patterns are formed on inner side 301 and/or outer side 302 of the light-guide mask 300, or forming a plurality of concave or convex geometrical structures on the inner side 301 and/or outer side 302 of the light-guide mask 300. Definitely, light-diffusing portion 310 may be formed by adding the diffusing particles at positions where the light-diffusing portions 310 are to be formed during the processing of the light-guide mask 300. The light-guide mask 300 is made of a light-transmissive material, and thus the light-guide mask 300 can be polishing on the inner surface 301 and/or outer surfaces 302 other than the light-diffusing portion, so as to avoid the rough surface of the inner side 301 and/or outer side 302 scatters the light rays.

In another word, the light-diffusing portion 310 can be contained all over the whole of the light-guide mask 300. The light-diffusing portion 310 has a plurality of light-diffusing structures. Each of the light-diffusing structures is at least one selected from a group consisting of mesh points, patterns, concave geometrical structures and convex geometrical structures. The density of the light diffusing structures at the area of the light-guide mask 300 with higher light intensity received is higher than the density of the light diffusing structures at the area of the light-guide mask 300 with lower light intensity received. Utilizing the light-diffusing portion 310 having the light-diffusing structures in the embodiment of FIG. 1, the density of light-diffusing structures on the area of the light-guide mask 300 corresponding to top of the light sources 200 is lower than that on the other area. The user can properly adjust the relative density of these two areas to have better performance in accordance with different kind of light sources 200.

The diffusing plate 400 is located on a side 302 of the light-guide mask 300 opposite to the light sources 200. The diffusing plate 400 can be disposed on the side wall 120, i.e., on the other end of the side wall 120 opposite to the end connecting the base plate 110. A light-mixing space is between the diffusing plate 400 and the light-guide mask 300, such that the light rays emitted from the light-guide mask 300 are mixed in the light-mixing space, and then incident to the diffusing plate 400, so as to be further diffused by the diffusing plate 400. The diffusing plate 400 is made of a transparent material, such as polymethyl methacrylate (PMMA) or poly carbonate (PC). The diffusing plate 400 may be manufactured by means of injection molding or pressure casting. The diffusing plate 400 may be formed by forming a plurality of inlcjet mesh points or patterns on an outer side 401 (and inner side) of a transparent substrate, or formed by forming a plurality of concave or convex geometrical structures on the outer side 401 and/or inner side 402 of the transparent substrate. Definitely, the diffusing plate 400 may also be formed by adding diffusing particles during the processing of the transparent substrate.

Portions of light rays emitted from the light sources 200 directly passes through the light-guide mask 300 while other portions of the light rays emit towards the base plate 110 and side wall 120. In order to have better light efficiency, the backlight module 10 further comprises a reflective layer 500. The reflective layer 500 is disposed between the base 100 and the light sources 200. Here, the reflective layer 500 is covered on the base plate 110 and the side wall 120, that is, the reflective layer 500 may be covered on the base plate 110 and the inner side of the side wall 120 near the light sources 200. The reflective layer 500 may be a reflective plate, or a reflective material coated on surfaces of the base plate 110 and the side wall 120. In another embodiment, the base plate 110 and the side wall 120 can be made of a transparent material. Therefore, the reflective layer 500 can be formed on the outer surfaces of the base plate 110 and the side wall 120 respectively.. The reflective layer 500 can be a base material of polyethylene terephthalate (PET) with white diffusing particles coated on the base material, for reflecting the incident light rays.

In this embodiment, in the backlight module 10, the light-guide mask 300 is disposed on the base plate 110 and covers the non-directional light sources 200. The light-diffusing portions 310 is designed on the light-guide mask 300, directing to the light-emitting characteristics of the non-directional light sources 200, such that the light rays emitted by the non-directional light sources 200 from thereabove pass through the light-guide mask 300. The light rays emitted by the non-directional light sources 200 towards two sides are diffused and then pass through the light-guide mask 300. In this manner, after passing through the light-guide mask 300, the light rays are preliminarily uniformized by the light-guide mask 300, and then mixed in the light-mixing space 430 between the light-guide mask 300 and the diffusing plate 400. After mixed in the light-mixing space 430, the light rays are scattered / diffused by the diffusing plate 400 for further uniformization to obtain a uniform planar light with higher brightness. By utilization of the light-guide mask 300, the light rays are scattered by the light-guide mask 300 to shorten the required height of the light-mixing space. In other words, height of the light-mixing space 403 is around 5.5 to 0.5 times than thickness of the light-guide mask 300 in a backlight module.

FIG. 2 is a schematic view of a module according to a second embodiment of the present invention. Referring to FIG. 2, the structure of this embodiment is substantially similar to the above embodiment, except that the light sources 200 used in this embodiment are directional light sources, such as light emitting diodes (LEDs), Laser Diodes (LDs) or Field Emission Display (FEDs). The light-emitting characteristic of the directional light sources refers to that the light rays emitted by every point on the light-emitting surface of the light sources 200 are converged in a specific angle range, such that the light rays out of the specific angle range has lower brightness.

In respect to the directional LEDs serving as the light sources 200, in this embodiment, the inner side 301 of the light-guide mask 300 corresponding to the light sources 200 includes parallel surfaces 301a and side surfaces 301b. The parallel surfaces 301a are substantially parallel to the light-emitting surfaces of the light sources 200. The side surfaces 301b are perpendicularly connected to one side of the parallel surfaces 301a respectively. The outer side 302 of the light-guide mask 300 may have a shape of corner column, and may have a geometrical shape such as a curved surface. The shape of the outer side 302 of the light-guide mask 300 varies according to different characteristics of the light sources 200.

The light-guide mask 300 is disposed on the base plate 110 and covers the directional light sources 200. The light-guide mask 300 has at least a light-diffusing portion 310. The location of the light-diffusing portion 310 varies according to different characteristics of the light sources 200. The light-diffusing portion 310 of the light-guide mask 300 is disposed on the light-guide mask 300 at a position corresponding to the light rays having a higher brightness emitted from the light sources 200, so as to diffuse the light rays incident to the light-guide mask 300. In the embodiment of FIG. 2, the lights emitted from the directional light sources 200 are concentrated at a position above the directional light sources 200, and thus the position above the directional light sources 200 is brighter. Therefore, the light-diffusing portions 310 are distributed on the light-guide mask 300 at positions above the directional light sources 200, so as to diffuse the incident light rays to reduce the light brightness above the directional light sources 200. The area other than the light-diffusing portions 310 allow the light rays having lower brightness emitted by the directional light sources 200 passing through the light-guide mask 300.

The light-guide mask 300 may be manufactured by a process such as injection molding or pressure casting. Moreover, when a plurality of light-guide masks 300 is used, the light-guide masks 300 may be integrally manufactured to cover the plurality of directional light sources 200, or manufactured separately as single structures to cover single or the plurality of directional light sources 200, i.e., the light-guide mask 300 covers the light sources 200 in a one-to-one manner, as shown in FIG. 3.

In this embodiment, in the backlight module 10, the light-guide mask 300 is disposed on the base plate 110 and covers the directional light sources 200. The light-diffusing portions 310 are designed on the light-guide mask 300, directing to the light-emitting characteristics of the directional light sources 200. Thus, the light rays emitted by the directional light sources 200 from thereabove are diffused and then pass through the light-guide mask 300 to reduce the light brightness at positions above the directional light sources 200. The portions other than the light-diffusing portions 310 allow the light rays having lower brightness emitted from the directional light sources 200 out of the specific angle range directly passing through the light-guide mask 300. In this manner, after passing through the light-guide mask 300, the light rays are preliminarily uniformized by the light-guide mask 300, and then mixed in the light-mixing space between the light-guide mask 300 and the diffusing plate 400, and incident to the diffusing plate 400 for further uniformization, so as to form the uniform area light with higher brightness. By utilization of the light-guide mask 300, the light rays are scattered by the light-guide mask 300 to shorten the required height of the light-mixing space. In other words, height of the light-mixing space is around 5.5 to 0.5 times than thickness of the light-guide mask 300 in a backlight module. Refer to FIGs. 4A, 4B, and 4C.

FIG. 4A is a schematic view of a conventional direct-type backlight module. In this direct-type backlight module, 24 CCFLs 201 are disposed with an interval of 21 mm.

FIG. 4B is a schematic view of another conventional direct-type backlight module. In this direct-type backlight module, the number of CCFLs is reduced as compared with the direct-type backlight module shown in FIG. 4A. Here, 16 CCFLs 201 are disposed with an interval of 32.3 mm.

FIG. 4C is a schematic view of an application of the backlight module according to the present invention. In this application, 16 CCFLs 201 are disposed in the backlight module with an interval of 32.3 mm, and the light-guide mask 300 is covered on the 16 CCFLs 201. The distance between the diffusing plate and the base may be 2 cm, and the distance between an outer side height point of the light-guide mask and a surface of the base may be 1 cm.

Please refer to FIG. 5. FIG. 5 is a schematic view of uniformity measurement of luminous flux of 9 points defined by conventional backlight module. The uniformity measurement of luminous flux for a backlight module 10 is firstly dividing into several areas, for examples 9 areas, 13 areas or 25 areas. According to FIG. 5, the backlight module 10 is divided into 9 areas.

The width of the backlight module 10 is W. The height of the backlight module 10 is H. 9 points are distributed as shown on FIG. 5 and have a light intensity, respectively. The highest light intensity I_MAX and the lowest light intensity I_MIN among all 9 point are used to calculate the uniformity. The uniformity of the luminous flux is (IMIN/I_MAX) ^X 100%.

Refer to FIGs. 6A, 6B, and 6C.

FIG. 6A shows an Advanced System Analysis Program (ASAP) simulation result taken at a mixing height of 2 cm of FIG. 4A. It can be seen from the figure that the uniformity of the light flux is larger than 92%. FIG. 6B shows an ASAP simulation result taken at a mixing height of 2 cm of FIG. 4B. It can be seen from the figure that the uniformity of light flux is larger than 80%.

FIG. 6C shows an ASAP simulation result taken at a mixing height of 2 cm of FIG. 4C. It can be seen from the figure that the uniformity of light flux is larger than 91%.

It can be seen from FIGs. 6A, 6B₅ and 6C that, in the same mixing distance, the reduced number of the light sources will cause lower uniformity of the light flux, thus causing obvious mura. When the number of the light sources is reduced, the light sources are covered by a light-guide mask, so as to effectively enhance the uniformity of the light flux, thus achieving the uniform area light same as that obtained with the number of the light sources remaining unchanged.

Refer to FIGs. 7 A and 7B.

FIG. 7A is a schematic view of a conventional direct-type backlight module using LEDs. A plurality of LEDs 202 is disposed.

FIG. 7B is a schematic view of a direct-type backlight module according to another embodiment of the present invention. The light-guide mask 300 is covered on a plurality of LEDs 202.

Refer to FIGs. 8A and 8B.

FIG. 8 A shows an ASAP simulation result taken at a mixing height of 2 cm of FIG. 7 A.

FIG. 8B shows an ASAP simulation result taken at a mixing height of 2 cm of FIG. 7B. It can be seen from FIGs. 8 A and 8B that, in the same mixing distance, a light-guide mask covered on the light sources can effectively enhance the uniformity of the light flux.

The backlight module of the present disclosure uses a light-guide mask to diffuse and then mix the light rays. In this manner, a uniform area light may be achieved in a small mixing distance instead of large mixing distance required in the prior art. In another aspect, with the same mixing distance, the similarly uniform area light in the prior art can also be achieved by reducing number of light sources in the present disclosure.

Claims

CLAIMSWhat is claimed is:

1. A backlight module, comprising: a base, having a base plate and a side wall; at least a light source, disposed above the base plate, for emitting light rays; at least a light-guide mask, disposed on the base plate and covering the light source, the light-guide mask having at least a light-diffusing portion, for diffusing the light rays incident to the light-guide mask; a diffusing plate, disposed on a side of the light-guide mask opposite to the light source to have a light-mixing space between the diffusing plate and the light-guide mask, the light rays from the light-guide mask mixed in the light-mixing space being incident to the diffusing plate and diffused by the diffusing plate.

2. The backlight module as claimed in claim 1, further comprising a reflective layer disposed on the base.

3. The backlight module as claimed in claim 1, further comprising a reflective layer disposed on the side wall.

4. The backlight module as claimed in claim 1, wherein the light-diffusing portion has a plurality of light-diffusing structures, each of the light-diffusing structures is at least one selected from a group consisting of mesh points, patterns, concave geometrical structures and convex geometrical structures.

5. The backlight module as claimed in claim 1, wherein the light-diffusing portion is located on an area of the light-guide mask having a higher intensity of light rays incident into the light-guide mask.

6. The backlight module as claimed in claim 1, wherein the light source is a non-directional light source.

7. The backlight module as claimed in claim 6, wherein the non-directional light source is a cold cathode fluorescent lamp or a hot cathode fluorescent lamp.

8. The backlight module as claimed in claim 6, wherein the backlight module has a plurality of the light sources, the light intensity received by the area of the light-guide mask corresponding to top of the light sources is higher than the light intensity received by the peripheral area of the light-guide mask corresponding to other area of the light sources, and the light diffusing portion is located at the peripheral area of the light-guide mask.

9. The backlight module as claimed in claim 1, wherein the light source is a directional light source.

10. The backlight module as claimed in claim 9, wherein the light source is a light emitting device (LED), a laser diode (LD) or a field emission display (FED).

11. The backlight module as claimed in claim 9, wherein the light-diffusing portion is located corresponding to the light direction of the directional light source.

12. The backlight module as claimed in claim 9, wherein the light-diffusing portion is contained all over the whole of the light-guide mask, the light-diffusing portion has a plurality of light-diffusing structures, each of the light-diffusing structures is at least one selected from a group consisting of mesh points, patterns, concave geometrical structures and convex geometrical structures, and the density of the light diffusing structures at the area of the light-guide mask with higher light intensity is higher than the density of the light diffusing structures at the area of the light-guide mask with lower light intensity.