How does the light diffusion working in LED light?

Light diffusion material refers to the material that can convert point and line light sources into line and surface light sources. generally speaking, the function of this kind of material is to make the light source look less dazzling to the naked eye after refraction, reflection, and scattering. So firstly, I will introduce what’s the common light diffusion materials in LED?

1. PS light diffusion lampshade
Preparation method.
At present, the main preparation 1methods of photodiffusion materials are polymerization and blending modification.

1.) Polymerization method.
According to the principle of light refraction, the polymerization method is based on the copolymerization of two kinds of polymer monomers with different refractive index and poor compatibility, or piecewise polymerization, which is used to further prepare light scattering light diffusion materials. Two kinds of monomers with different reaction activities are prepared by polymerization, because the reaction activity between the scatterer monomer and the monomer forming the matrix is different, and the scatterer monomer produces self-polymerization or block copolymerization with the matrix monomer. In this way, the optical properties of the condensed nucleus formed in the respective polymerization chain are uniform, and the light is reflected and refracted at the boundary of the condensed core, thus become forming scattering. Polymerization is widely used in the preparation of PMMA-based photodiffusion materials.

2. Light diffusion LED lampshade.
blending modification method.
The blending modification method is to add the light diffuser to the resin, which is spherical and uniformly dispersed in the transparent resin to form an island structure. As the different refractive index of the resin and the light diffuser, the light is similar to specular reflection on the surface of the light diffuser. After multiple reflections to achieve the effect of light diffusion. At the same time, the amount of optical diffuser, particle size, and distribution, refractive index determine the optical properties of the material.

3. Light diffusion lampshade.
At present, many light diffusion materials are generally produced by this method, because this method is similar to polymer doping, and the process is simple, especially in the light diffusion plate with a very large dosage, this method can be produced continuously and has high production efficiency.
Below is an example mainly based on the blending modification method :

1.) Action mechanism.
The action mechanism of light diffusion material is that organic or inorganic particles are added to the diffusion plate substrate as scattering particles to make light refraction, reflection, and scattering in two media with different refractive index when passing through the scattering layer. so it can produce the effect of optical diffusion. Details please check the diffusion schematic diagram as follows:

2.) Matrix material.
As the substrate of light diffusion materials, high light transmittance is required. The common matrix materials include PPMMA, PS, and PC,-based light diffusivity as follows:

The refractive index determines how bright the material looks, and a higher refractive index indicates that more light is reflected at the interface between the material and the air. Generally speaking, the higher the refractive index, the lower the transmittance.

PC light diffusion lampshade
3.) Light diffuser
According to the composition of light diffusion agent, it can be divided into the organic diffuser and inorganic diffuser.

Organic light diffuser
This kind of light diffusion agent mainly includes acrylic type, silicone type, polyvinyl type, and so on. At present, acrylic and silicone light diffusion agent are the most widely used. This kind of light diffuser has good transmittance. Silicone has the advantages of low addition and good haze, and the transmittance of acrylic acid is good.

Light diffusion LED lampshade
Inorganic light diffuser
Inorganic light diffusers mainly include nano-barium sulfate, silicon dioxide, calcium carbonate, and so on. From a microscopic point of view, these inorganic light diffusers are solid microspheres, and it is very difficult for light to pass through the solid sphere, which will affect the transmission of a lot of light. only part of the light is refracted through, so it affects the brightness or transmission of light, which is rarely used at present.
The refractive indices of several light diffusers are as follows:

LED lampshade
4.) Influence of light diffusion particles
Effect of diffusion particle size
In the case of the same mass, the smaller the particle size is, the more the number of particles; the more times the light is deflected when passing through, and the greater the diffusivity is, the higher the haze is. However, when the particle size is too small, the particle size distribution is difficult to control, on the contrary, in same haze, the transmittance decreases. Only when the particle size and particle size distribution are proper, the light transmittance and haze can reach a higher value at the same time. The particle size is generally about 1-5 microns. At the same time, the better the regularity and finish of the particles, the better the haze and light transmittance.

LED lamp
Effect of Refractive Index of diffused particles
The refractive index of the substrate and the diffuser should not be too large or too small. When the relative refractive index of the diffuser is between 0.91-0.97 and 1.03-1.09, the diffusivity transmittance is better. If the relative refractive index is too small, there is little difference between the two refractive indexes and the scattering is not obvious. A large difference in the relative refractive index will lead to total reflection, which reflects the light back inside and cannot be effectively exported.

Light diffusion LED sheet
Effect of diffusion particle concentration.
With the light diffusion particles increased, the number of light scattering in the diffusion plate will be increased, the backscattering increases, the free path of photons decreases, the haze increases, but the transmittance decreases. In the case of ensuring high transmittance and haze, the concentration of light diffusion material is reasonably selected, and the general mixing ratio is less than 2%.

Light diffusion LED lamp
3. Performance Requirements.
Common LED light diffusion materials require the following:
High transmittance, high diffusion, no glare, no light, and shadow.
The concealment of the light source is better.
It has good flow processability, dimensional stability, weather resistance, and heat resistance.
High flame retardant and high impact strength.
The light transmittance is more than 80%.

Light diffusion LED lamp
Characteristics of Light Diffusion Materials.
The advantage of the light diffusion material is that under the premise of ensuring the high light transmittance, it increases the light diffusivity and haze of the product. through the action of the diffusion plate, the whole board forms a uniform luminous surface without forming a dark area. At present, the optical diffusion plate is divided into PC optical diffusion plate, PMMA optical diffusion plate, and PS optical diffusion plate. However, PMMA is not scratch-resistant, and PS is not heat-resistant and flame-retardant. At present, PC is widely used in LED lampshades. The following is a comparison of several kinds of light diffusion plates.