The present invention relates to a diffuser plate having a surface microstructure, and more particularly to a diffuser plate that utilizes a base plate, a microstructure, and an arc-shaped reflecting cover to provide many advantages including high light transmission rate, promoted brightness and uniform light beams.
The general direct backlight module cannot satisfy the requirement of providing uniform brightness in the absence of optical film. It means that the brightness distribution of the backlight module is very poor when the human eyes look at different positions of the backlight module. It is apprehensible that the upper light beams of the lamp are allowed to enter the eyes directly, but the farther light beams can not be diffused to the dark region beside the lamp and the light beams can not be focused into the retinas of the eyes. This backlight phenomenon of extreme non-uniform brightness is usually called as MURA defects. A diffuser plate and a diffuser film are essential for the direct backlight module to improve the MURA defects caused by the non-uniform light source or lamp.
The diffuser plate of the current direct backlight module is generally made of a transparent polymer having diffusion particles doped therein. Moreover, the semi-sphere (or called as lenticular) refraction structure is further formed on the light-ejecting surface and the light-injecting surface of the diffuser plate so as to improve diffusion effect. But, the aberration usually exists in the semi-sphere microstructure and the light beams emitted from the light sources cannot enter the retinas. As a result, the diffusion angle of the light beam is so large that the human eyes can only sense partial brightness because the human eyes have limited filed of view.
The interval among the lamps is increased while the amount of the lamps in the 32 inches LCD TV is decreased, for example, from sixteen lamps to twelve lamps. As a result, the thickness of the backlight module must be increased so as to increase the diffusion and reduce the MURA defects instead of merely utilizing the diffusion particles and the arc-shaped reflecting structure. However, the increase of thickness violates the purpose of forming thinner backlight module. Therefore, in order to reduce the amount of the lamp and the size and weight of the backlight module, a new design must be introduced into the future diffuser plate so as to allow the light beams to enter the eyes and to maintain a certain amount of brightness and uniformity.
A main object of the present invention is to form a microstructure on a light-ejecting surface or a light-injecting surface of the base plate so as to confine the half viewing angle and increase the intensity at 0° viewing angle, wherein the microstructure is formed in accordance with the design principle of the Fresnel lens and the Snell's law. For the purpose of maintaining the uniformity of the light beams that pass through the base plate, the special arc-shaped reflecting cover is utilized to reflect partial light beams emitted from the light sources to the base plate so that the half viewing angle can be confined to ±10 degrees. In addition, the intensity at 0° viewing angle is obviously increased by 125%.
Referring to
The light sources 1 are Cold Cathode Fluorescent Lamps (CCFLs) or LED arrays. These light sources 1 are equally separated by a certain interval PL.
The reflecting cover 2 has continuously linked arcs having a radius of 0.5 to 0.75 times the interval PL. The aforesaid light sources 1 are held in the reflecting cover 2. The reflecting cover 2 is made of a material selected from a group consisting of polymethylmethacrylate (PMMA), polycarbonate (PC), methylmethacrylate styrene (MS), polystyrene (PS), Al, Ag, Ni, Cu, and Sn. The reflecting cover 2 is designed for reflecting partial light beams emitted from the light sources 1 so as to further focus the light beams.
The base plate 3 is disposed above the light sources 1, and it is made of a light-transmitting polymer including polymethylmethacrylate (PMMA), polycarbonate (PC), methylmethacrylate styrene (MS), or polystyrene (PS). The base plate 3 has a UV absorbent 31 doped therein to prevent the direct UV light irradiation from causing the base plate 3 to generate the phenomena of photo yellowing and cracking. In addition, the base plate 3 has several diffusion particles 32 doped therein, wherein the diffusion particles 32 are selected from a group consisting of polymethylmethacrylate (PMMA), polycarbonate (PC), methylmethacrylate styrene (MS), polystyrene (PS), silica, silicon, melamine, calcium carbonate, Teflon, TiO2 and SiO2. As a result, the phenomenon of optical diffusion occurs when the light passes through the diffusion particles 32.
The microstructure 4 is formed on a light-ejecting surface or a light-injecting surface of the aforesaid base plate 3. The microstructure 4 comprises several superfine patterns 41. These patterns 41 have several curved parts 411 that have different widths P, different angles θ, and different corresponding depths H from one another. The widths P of the curved parts 411 are ranged between 0.05 mm and 0.5 mm. The curved parts 411 have different angles θ, which are designed in accordance with the same design principle of the Fresnel lens. The parameters required for designing the curved parts 411 are decided by the amount N of the afore-mentioned light sources 1, the interval PL between two light sources 1, the first distance Z1 between the light source 1 and the base plate 3, and the second distance Z2 between the light source 1 and the reflecting cover 2. The interval PL is defined as a period. The lens has a back focal length defined to be the first distance Z1 plus the second distance Z2. Besides, the lens has a front focal length defined to be an infinite distance. In addition, the angles θ of the curved parts 411 are defined in accordance with the Snell's Law. In other words, if there are N light sources in the backlight module, the microstructure 4 has N periodical patterns 41, wherein the change rates of the angles θ of the curved parts 411 within the same period are all the same. Referring to
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By using the aforesaid technology, the second preferred embodiment of the present invention has the following advantages: (1) the second preferred embodiment can control the directions of the light beams better than the first preferred embodiment by using the dual-surface microstructures 5 and 6; (2) the dual-surface microstructures 5 and 6 of the second preferred embodiment can share the excessive large angle caused by the single-surface microstructure 4 of the first preferred embodiment, which causes excessive depth and affects the ability to demold. As a result, by using the dual-surface microstructures 5 and 6 of the second preferred embodiment, the optical property can be maintained while the structure's depth is half reduced.
It deserves to be specially noted that the microstructures 4, 5, and 6 of the first and second preferred embodiments can be formed by extrusion, co-extrusion, and ejection process. The thickness of the base plate 3 is ranged between 0.08 mm and 3.0 mm. The base plate can be a single layer or a sandwich structure by using the extrusion process or the co-extrusion process. The sandwich structure can be divided into core and sub layers. The total thickness of the diffuser plate is ranged from 0.08 mm to 3.0 mm. The thickness of the sub layer is ranged from 50 μm to 200 μm.