Introduction to Cold Light Source and Hot Light Source

Cold light source: Cold light source is a light source stimulated by chemical energy, electrical energy, bioenergy, etc. (fireflies, neon lights, LEDs, etc.), which has very good optical and flickering characteristics. When an object emits light, its temperature is not higher than the ambient temperature. This kind of light emission is called a cold light source. For example, LED emits light by the recombination of electron-hole pairs. Strictly speaking, LED light is electroluminescent and also generates heat, but it is a little lower than light sources such as incandescent lamps. The LED electro-optical conversion efficiency is about 30%, of which the internal quantum efficiency is about 70% (close to the theoretical limit) and the external quantum efficiency is about 50%. (This is only experimental data, not an accurate value)

　　Thermal light source: a light source that uses thermal energy to excite, such as an incandescent lamp that emits light through thermal radiation at a temperature of 3000-4000K. Incandescent lamps convert 80-90% of their energy into thermal energy, and about 10% into light energy. Therefore, the luminous efficiency is low. We do not define it as a cold light source or a thermal light source based on the temperature of the lamp housing. The temperature around the lamp can only judge the quality of the lamp's heat dissipation measures.

　　The difference between cold light source and heat light source cannot be distinguished only by definition. In fact, what we call cold light source does not mean that no heat is generated during the light emission process, but that the light emission method is not the conversion of heat energy into light energy. Incandescent lamp is a typical process of converting electrical energy into heat energy, and then converting heat energy into light energy. The heat energy loss is high and the luminous efficiency is low. According to the current development trend of LED white light, the era when cold light source replaces heat light source is not far away, so we can regard LED as cold light source.