As a kind of the third generation light source, the performance index of LED includes the optical and electrical parameters of electric light source. Electrical parameters are voltage, current and power. Because LED is driven by DC, and both voltage and current are DC, the electrical performance index is, but the relationship between LED current and voltage is not linear.

　　Optical parameters include light energy, spectral energy release, chromaticity coordinates and display index (white light) and spatial distribution of light intensity. These parameters are defined in the same way as the light source. Monochromatic LED is a narrow-band spectrum, its spectral bandwidth is generally 20-35nm, while white LED has different output spectrum according to different generation mechanism. The spatial distribution of light output of LED is directly related to the packaging structure. Generally, the output light angle of LED for display is small, while that of LED for lighting is large.

　　LED light output is greatly affected by temperature, so the temperature curve of output luminous flux is very important. As a light source, life is an important index, the theoretical life of LED is more than 100000 h, but the actual LED is difficult to achieve the theoretical value due to the chip and packaging reasons.