Some Knowledge About Diffuser Plates

Diffusion plate English: Diffusion plate Its purpose is to interfere with the propagation of light, no matter how many degrees the originally planned light distribution curve is, just passing through the diffuser plate will make the beam angle 160~176°. When we look at the surface light source with the diffuser plate from the side, we will feel a layer of fog, which is the proof that the beam angle is as large as 160~176°.

The larger the beam angle, the lower the illumination, and some of them will have filtering effect - making some wavelengths impenetrable, resulting in color shift, such as re-drying and processing on the surface (for example: frosting, embossing) The light rate will be lower and lower due to the natural phenomenon of geometry, so the material used to make the diffuser plate should be made of materials with a lower refractive index, so as to reduce the interference to light.

According to the classification of optical principles, the diffuser is divided into two types: one is to increase the beam angle, and the other is to maintain the original angle.

Classification by material: glass, polystyrene (PS), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) ), acrylic (PMMA), acrylic (MMA).... etc. light-transmitting polymeric materials or constituent materials can be made into dispersion materials for different purposes.

When light travels from one medium to a smooth interface of another medium, part of the light is reflected by the interface, and another part of the light is refracted in the other medium through the interface. The incident angle of light is equal to the reflection angle, and the reflected light and the incident light are on both sides of the normal in the same plane, which is the law of reflection.

The refracted ray conforms to the law of refraction: the refracted ray is located in the plane of the incident light and the normal, the refracted light and the incident light are on both sides of the normal, and the ratio of the sine of the incident angle to the refracted angle is a constant. The law of refraction and the law of reflection are the foundations of geometric optics. They not only lay the foundation for theoretical research, but also for the development of optical technology and the design of optical products.

The light diffuser is a physical phenomenon of refraction, reflection and scattering that occurs when light encounters two media with different refractive indices on the way through chemical or physical means. Add inorganic or organic light dispersants to the base, or arrange the array of micro-features through the surface of the substrate to artificially adjust the light, make the light refract, reflect, and scatter in different directions, and then change the light's travel route to complete the incident light. Abundant dispersion produces the effect of optical dispersion. Light diffusers are widely used in liquid crystal display, LED lighting and imaging display systems.

Diffuser plate

Generally, the optical function quality control of transparent and translucent plastics such as plate, sheet, film, and tube is mainly used to evaluate the objectives of transmittance and haze. my country was proposed by the former Ministry of Chemical Industry of the People's Republic of China, drafted by the former Ministry of Chemical Industry Chenguang Chemical Research Institute and other units, and issued by the State Administration of Standards. On September 1, 1981, a "Transparent Plastic Light Transmission and Haze Test Method" ". The definitions are as follows:

1. Light transmittance - the ratio of the luminous flux (Luminous Flux) passing through the sample to the luminous flux hitting the sample, expressed as a percentage.

2. Haze—the ratio of the scattered luminous flux deviating from the incident light direction through the sample to the transmitted luminous flux, expressed as a percentage (for this method, only the scattered luminous flux deviating from the incident light direction by more than 2.5 degrees is used to calculate the haze) . The cloudy or cloudy appearance of the interior or exterior of a transparent or translucent material due to light scattering. Expressed as a percentage of the ratio of the scattered luminous flux to the luminous flux transmitted through the material. It is an important parameter for the optical transparency of transparent or translucent materials.

3. Refractive index - no matter how your transmittance or haze change, the quality (density) of the object determines its optical properties. The higher the refractive index, the lower the transmittance, and it has nothing to do with thickness. Both light transmittance and haze are targets for measuring material transparency, and are not necessarily applicable to diffusers. Generally speaking, there is an inverse relationship between light transmittance and haze.

The above is the definition of transparent materials. In the 1980s, the domestic transparent plates were not transparent enough, and the foreign standards were quoted. After all, in 1981, there was no country or region that made clear standards for the definition of diffuser plates. , Even in 2014, there is no official standard. The term Z has long been derived from the direct-illuminated backlight module, so the diffuser plate cannot be fully explained by citing the standard of the transparent plate, nor is it a standard formulated by my country. Therefore, it is not necessarily suitable for solid-state lighting. With the development of LED light source and LED lighting, its application presents a technical bottleneck. Since none of the domestic manufacturers have optical engineering experts, they are still in the processing stage.

Optical eigenvalue detection method of diffuser plate

1. Illuminance meter: This kind of instrument is cheap and easy to carry, but due to the interference of external natural light, the value of the test will generally be high. This kind of instrument is only suitable for reference and comparison, not as an instrument.

2. Light transmittance haze tester: This instrument is less affected by the outside world during the test, so the test results are lower than the illuminance tester, but more accurate. Generally, diffuser plate manufacturers use this instrument to test the transmittance and haze of their own products. .

3. Integrating sphere: The light transmittance of the diffuser plate is very accurate in the integrating sphere test, and it is hardly disturbed by the external environment, so the data obtained by testing the same plate is lower than the above two. Because the instrument is relatively expensive, only large lighting companies use this equipment to detect light transmittance. (Note: The size of the integrating sphere, the orientation of the placement, the distance from the probe, the angle between the probe and the light source and other factors will affect the result of the test).

4. Light intensity distribution: Light intensity distribution is an objective tool for whether a light source has commercial value, because only using it is a complete optical integrity test for a light source. Some of the other above-mentioned things are only the measurement of light molecules or the definition of a material. When this material is added to this lamp, it can only be used to measure whether it conforms to the rules of the International Lighting Association.

Therefore, in view of the different testing instruments used, the measured light transmittances are not the same. When choosing a diffuser, you must ask what kind of light transmittance is used to detect the light transmittance. This will not be far from the product you expect. .

The diffuser plate is widely used in liquid crystal display, LED lighting and imaging display systems. Its main function is to fully diffuse the incident light and achieve a softer and uniform irradiation effect.

Applied to the direct type backlight system used in LCD TV, the diffuser plate has good functions such as heat resistance, dimensional stability, mechanical strength, flame resistance, etc. Its light dispersion effect reaches the ideal state. It has high brightness and high dispersion, which can improve the uniform dispersion of the luminous distribution of the backlight.

Requirements for diffuser panels in machine vision lighting:

1. Dispersion function: high light softness;

2. High light transmission function: reduce energy consumption and improve the illumination of LED;

3. Light source influence: keep the color temperature of the light source consistent;

4. Dimensional stability: The water absorption rate is small, and it can maintain good dimensional stability in a humid environment, and can be used normally in the temperature range of -40℃~125℃;

5. Antistatic: It has good surface antistatic function to prevent dust adsorption.