What is the difference between hot light source and cold light source

Cold light source is the use of chemical energy, electrical energy, biological energy to stimulate the light source (fireflies, neon lights, LEDs, etc.). Has a very good optical, variable flash characteristics. Object luminescence, its temperature is not higher than the ambient temperature, this luminescence is called cold light source, such as LED is the use of electron-hole pair compound luminescence. From a strict sense, LED light-emitting diode is electroluminescence is also heat generation, just relative to incandescent light sources such as low point.LED electro-optical conversion efficiency of 30% or so, of which the internal quantum efficiency of 70% or so (close to the theoretical limit), the external quantum efficiency of about 50%. (This is only experimental data, and not the exact value)

Thermal light source: the use of thermal excitation of the light source, such as incandescent lamps in the 3,000-4,000K temperature when the thermal radiation luminescence. Incandescent lamps have 80-90% of the energy converted to thermal energy, about 10% of the energy converted to light energy. Therefore the luminous efficiency is low. We are not based on the temperature of the lamp shell to define the cold light source, or hot light source. The temperature around the lamp can only be judged by the advantages and disadvantages of the lamp's heat dissipation measures.

Differentiating between cold light source and hot light source, we can't only distinguish from the definition. In fact, what we call cold light source does not mean that the luminous process does not produce heat, but refers to the way the light is not converted from heat energy to light energy. Incandescent lamps are typically converted from electrical energy into heat, and then the process of converting heat into light. Higher heat loss, low luminous efficiency, according to the current development trend of LED white light to see the cold light source to replace the hot light source of the era is not far away. Therefore, we can regard LED as a cold light source.