LEDs for LCD backlighting are divided into edge lighting mainly for medium and small equipment and direct lighting for large area equipment such as LCD-TV.
1, Edge Lighting
The basic structure of Edge lighting is shown in Figure 1.
figure 1
The light emitted by the LED is emitted upward into a surface light source through the optical action of the Light Guide Plate, and a spot of uniform brightness and color is formed at the LCD panel through a Diffuser Plate and a brightness enhancement film (BEF).
The diffuser can increase the uniformity of light distribution. The brightness enhancement film can concentrate the light to a certain angle on the front side to improve the frontal brightness. However, excessive use of the diffusion plate and the brightness enhancement film will increase the light loss, reduce the overall light efficiency, and diffuse the plate and increase the light. The film has been monopolized by the patent and the cost is high. Therefore, increasing the uniformity of direct light emission from the light guide plate through optical design is the focus of the side-down backlight design.
The optical design of the front end is mainly divided into: (1) the design of LED light coupling into the light guide plate (2) the optical structure design of the light guide plate
1.1 LED and light guide light coupling
(1) Direct coupling
The structure diagram is shown in Figure 2. Generally speaking, direct coupling can improve the efficiency of LED light entering the light guide plate. The structure is simple, but at the same time, the RGB three-color light is not fully mixed before entering the light guide plate, which may result in uniform color of the final light output. Poor sex, especially for structures where the light path is shorter in the light guide.
figure 2
(2) Indirect coupling
The structure diagram is shown in Figure 3. The advantages of indirect coupling are twofold: (1) scattering and atomization before light enters the light guide plate to improve uniformity (2) full color mixing
image 3
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