Power LEDs are used in the field of lighting, and secondary optical lenses are used to achieve good light distribution. The lenses of various properties designed to meet different effects are mostly optical grade acrylic (PMMA). Its light transmittance is about 92%.
You may have to say, yeah, the material transmittance is 92%. Why do you say 99%?
The guest officer is in a hurry, listen to me:
There are two main reasons for causing light loss:
1. Reflection loss at the transmission interface
2. Absorption loss of optical material itself
The loss of light caused by interface reflection is often neglected, and everyone is more concerned with the absorption of the material itself.
In fact, for a lens with a high transmittance and a small volume, the loss caused by the interface reflection is far greater than the loss absorbed by the material itself.
What is the interface reflection loss?
When the light passes through the interface with different refractive index, interface reflection occurs, and there is a certain reflection loss.
The ratio of the reflected light flux to the incident light flux is called the reflection coefficient (reflectance).
Therefore, when the ordinary lens is used, the light is lost like this:
Suppose the light emitted by the chip is 104.
Through a lens (package), after a single interface loss of 4%, leaving 100;
When entering the secondary lens, another interface loss of 4%, leaving 96;
From the secondary lens, it is an interface loss of 4%, and finally 92.
Figure: Light loss of a normal lens
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