The Principle Of Side-guided LED Backlight

  The basic principle of the side-guided LED backlight is to use the principle of total light reflection to effectively transmit light and transform the line light source into a surface light source. Principle of total light reflection: When light is refracted from a medium with a high refractive index to a medium with a low refractive index (such as plastic to air), the refracted light is emitted at an oblique angle than the light from a person. When the angle of the person is greater than a certain When the angle is angled, the light cannot be refracted in the air and all inward reflection occurs, which is called total reflection or internal reflection. When the angle of refraction is equal to 90", the angle of incidence is called the critical angle.

       According to the law of light refraction and the formula n-1,Sinθ,=n2Sinθ2, the critical angle θc=Sin-1(n 2,Sin90°/n2)=Sin-1(n2/n1) can be deduced, and it is known that n2=1 (air ), n1=1.491 (light guide plate plastic PMMA material), θc=Sin -10.6707=41.8°, that is, when the light inside the light guide plate is greater than 41.8°, total reflection will occur, and the light will follow the guide The direction of the light plate is transmitted from one side to the other. For the light guide plate made of PMMA material, the light transmittance is as high as 92%, the haze is very small, and the light absorption is very small. The light can travel a long distance along the board with little attenuation. . The purpose of the light guide plate is to refract light from the surface to form a bright and uniform surface light source. Therefore, the technical principle of the light guide plate is to use the principle of total light reflection for light transmission, on the other hand, to use it the other way around, destroy the condition of total light reflection, interfere with the optical elements of total internal reflection of light, and change the optical path of light. , The light is led out from the surface of the light guide plate to form a surface light source to become a backlight plate. The specific design is to print white dots on the bottom surface of the light guide plate or injection molding into small bumps, so that the light will be diffusely reflected on the dots. Part of the light is incident on the light guide plate at an angle less than the critical angle and refracted, and part of the light is fully reflected. Reflected back into the light guide plate, these light rays are totally reflected on the upper edge of the light guide plate and return to the point on the bottom surface. This process keeps repeating, until some of the light is refracted from the surface, some is absorbed by the light guide plate, and some is lost to a certain interface. The light refracted from the surface is seen by the human eye, and this part of the light is really the light guide plate. The contribution of the backlight board is the brightness of the backlight source measured by the instrument.