Cold light source: cold light source is the use of chemical energy, electrical energy, biological energy source (firefly, neon light, LED and so on). It has excellent optical and flicker characteristics. When an object glows, its temperature is not higher than the ambient temperature, which is called a cold light source, for example, LED is a compound luminescence using an electron hole. In a strict sense, the LED light emitting diode is electroluminescent, which is also generated by heat, but is a little lower than the incandescent light source. The electrooptic conversion efficiency of LED 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 just experimental data, not the exact value)

Heat source: the light source that is excited by heat, such as the incandescent lamp, radiates at the temperature of 3000 - 4000K. Incandescent lamp with 80-90% energy conversion energy, about 10% of the energy for energy conversion. Therefore, the luminous efficiency is low. We do not define the temperature as a cold light or a heat source according to the temperature of the shell. The temperature around the lamps and lanterns can only be judged by the advantages and disadvantages of the radiating measures of the lamp.

We can't distinguish between the definition of the cold light and the heat source. In fact, the cold light source we say does not mean that it does not produce heat in the process of light, but means that the way of light is not converted from heat to light energy. Incandescent lamps are typically converted from electrical energy to thermal energy and then converted 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, it is not far away from the time of replacing the hot light source with cold light source. So we can think of LED as a cold light source.

Cold light source: cold light source is the use of chemical energy, electrical energy, biological energy source (firefly, neon light, LED and so on). It has excellent optical and flicker characteristics. When an object glows, its temperature is not higher than the ambient temperature, which is called a cold light source, for example, LED is a compound luminescence using an electron hole. In a strict sense, the LED light emitting diode is electroluminescent, which is also generated by heat, but is a little lower than the incandescent light source. The electrooptic conversion efficiency of LED 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 just experimental data, not the exact value)