The light diffusing material in LED lamps is like this

LED semiconductor lighting network light diffusing material refers to the material that can convert point and line light sources into line and surface light sources. Generally speaking, the role of such materials is to make the light source look like the naked eye after refraction, reflection and scattering. Stinging. That small series will lead everyone to understand the common light diffusing materials in LEDs .

â–²PS light diffuser

Preparation

At present, the preparation methods of the light diffusion material mainly include a polymerization method and a blend modification method.

First, the polymerization method

The polymerization method is based on the principle of light refraction, selecting two polymer monomers having a certain difference in refractive index, poor compatibility, or using segmental polymerization to further prepare a light-scattering light-diffusing material. Two kinds of monomers with different reactivity are prepared by polymerization, because the scatterer monomer has different reactivity with the matrix-forming monomer, and the scatterer monomer is self-polymerized or copolymerized with the matrix monomer, such two monomers The optical properties of the condensed core formed in the respective polymer chains are uniform, and the boundary light at the boundary of the condensed core is reflected and refracted, thereby forming scattering. The polymerization method is widely used in the preparation of PMMA-based light diffusing materials.

â–²Light diffusion LED lampshade

Second, the blending modification method

The blending modification method is to add a light diffusing agent to the resin. The light diffusing agent is spherical and uniformly dispersed in the transparent resin to form a sea-island structure. Since the refractive index of the resin and the light diffusing agent are different, the light is similar to the specular reflection on the surface of the light diffusing agent. After multiple reflections, the light diffusion effect is achieved. At the same time, the amount of light diffusing agent added, particle size and distribution, and refractive index determine the optical properties of the material.

â–²Light diffuser

At present, many light-diffusing materials are generally produced by this method, because this method is similar to polymer doping, and the process is simple, especially in the case of a very large amount of light-diffusing sheet, which can be continuously produced and produced. efficient.

The following is mainly based on the blending modification method.

Mechanism of action

The mechanism of action of the light diffusing material is mainly to add organic or inorganic particles as scattering particles in the diffuser substrate, so that the light is refracted, reflected and scattered in the two media with different refractive indices when passing through the scattering layer. This produces the effect of optical diffusion. As shown below:

â–²Light diffusion schematic

2. Base material

The substrate as a light diffusing material is required to have a high light transmittance. Common base materials are mainly PPMMA, PS and PC, and the base light diffusivity is as follows:

The refractive index determines how bright the material looks. A larger refractive index indicates that more light is reflected at the interface between the material and the air. In general, the higher the refractive index, the lower the light transmittance.

â–²PC light diffuser

3. Light diffusing agent

According to the composition of the light diffusing agent, it can be divided into an organic diffusing agent and an inorganic diffusing agent.

Organic light diffusing agent

This type of light diffusing agent mainly includes acrylic type, silicone type, polyethylene type, etc., and the most widely used ones are acrylic and silicone light diffusing agents. This type of light diffusing agent has a good transmittance. Silicone has the advantages of less added amount and good haze, and acrylic acid has a better transmittance.

â–²Light diffusion LED lampshade

Inorganic light diffusing agent

Inorganic light diffusing agents are mainly: nanometer barium sulfate, silicon dioxide, calcium carbonate, etc. These inorganic light diffusing agents are microscopically a solid bead ball, and it is difficult for light to pass through a solid sphere, which will affect many light rays. Through transmission, only part of the light passes through the refraction, thus affecting the brightness or light transmission, which is currently used less.

The refractive indices of several light diffusing agents are as follows:

â–² LED lampshade

4. Influence of light diffusing particles

Influence of particle size of diffusion particles

The smaller the particle size, the larger the number of particles in the same mass, the more the number of deflections when the light passes through, the greater the diffusivity produced, and the higher the haze. However, if the particle diameter is too small, the particle size distribution is difficult to control, and the transmittance is lowered in the case of the same haze. The particle size and particle size distribution are appropriate, and the light transmittance and haze can reach a high value at the same time. The particle size is generally around 1-5 microns. At the same time, the better the regularity and smoothness of the particles, the better the haze and the transmittance.

â–²LED lights

Influence of the refractive index of the diffusing particles

The refractive index of the substrate and the diffusing agent should not be too large, and should not be too small. When the relative refractive index of the diffusing agent is between 0.91 and 0.97 and 1.03-1.09, the diffusivity transmittance is relatively good. When the relative refractive index is too small, the refractive index difference between the two is small, and the scattering is not obvious. Excessive relative refractive index differences will cause total reflection to occur, reflecting light back into the interior and not being effectively derived.

â–² light diffused LED lights

Effect of diffusion particle concentration

As the light-diffusing particles increase, the number of times the light is scattered in the diffusing plate increases, the backscattering increases, the free path of the photon becomes smaller, the haze increases, but the transmittance decreases. The light diffusion material concentration is reasonably selected in the case of ensuring higher transmittance and haze, and the general addition amount is within 2%.

â–² light diffused LED lights

Third, performance requirements

Common LED light diffusion materials are as follows:

High light transmission, high diffusion, no glare, no light and shadow

The light source is better concealed

Good flow processability, dimensional stability, weather resistance, heat resistance

High flame retardant and high impact strength

Light transmittance exceeds 80%

Light diffusing LED light

Characteristics of light diffusing materials

The advantage of the light diffusing material is that under the premise of ensuring high light transmittance, the light diffusivity and haze of the product are increased, and the entire plate surface is formed into a uniform light emitting surface without forming a dark region by the action of the diffusing plate. At present, the light diffusing plate is divided into a PC light diffusing plate, a PMMA light diffusing plate and a PS light diffusing plate. However, PMMA is not scratch resistant, and PS heat resistance is poor. Currently, the material of PC is used more in LED lampshades. Below is a comparison of several light diffusers.

â–²LED light diffuser