Light is a form of energy that can be released by atoms. It is composed of many small particles with energy and power but no mass. These particles are called photons and are the most basic unit of light. Photons are released by the movement of electrons. In an atom, electrons move in the form of orbits around the atom. Electrons have different energies in different orbital functions.

　　 Generally speaking, electrons with greater energy move away from the nucleus through orbits. When an electron jumps from a lower orbit to a higher orbit, the energy level will increase. Conversely, when an electron drops from a higher orbital function to a lower orbital function, it releases energy. Energy is released in the form of photons. When the energy drops, higher-energy photons are released, which is characterized by their high frequency. Free electrons fall into the air holes from the P-type layer through the photodiode. This includes falling from the conduction band to a lower orbital function, so electrons release energy as photons. This will happen in any photodiode. In any photodiode, you can only see such a situation, you can not see such a photodiode.

　　 Visible light emitting photodiodes, such as digital display clocks, the size of the gap determines the frequency of photons, in other words, it determines the color of light. When all photodiodes emit light, most of them are not very effective. In ordinary photodiodes, the semiconductor material itself attracts a large amount of light energy, which is over. The light-emitting photodiode is covered by a plastic bulb and illuminates it in a specific direction.