Cold light source: The cold light source is a light source (firefly, neon, LED, etc.) excited by chemical energy, electric energy, bio-energy, etc., and has excellent optical and flashing characteristics. When an object emits light, its temperature is not higher than the ambient temperature. This kind of illumination is called a cold light source. For example, an LED uses a combination of electron-hole pairs to emit light. Strictly speaking, LED light-emitting diodes are electro-luminous, and there is heat generation, which is only a low point compared to 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 just experimental data, not an exact value)
Thermal light source: A light source that is excited by thermal energy, such as an incandescent lamp that emits heat at a temperature of 3000-4000 K. Incandescent lamps have 80-90% energy conversion energy, and about 10% energy is converted into light energy. Therefore, the luminous efficiency is low. We are not defined as a cold light source or a thermal light source depending on the temperature of the lamp housing. The temperature around the lamp can only judge the pros and cons of the heat dissipation measures of the lamp.
Different from cold light source and hot light source, we can't just distinguish by definition. In fact, the cold light source we refer to does not mean that heat is not generated during the process of light emission, but that the way of light emission is not converted from heat energy to light energy. Incandescent lamps are processes that typically convert electrical energy into thermal energy and then convert thermal energy into light energy. The thermal energy loss is high and the luminous efficiency is low. According to the current development trend of LED white light, the era of cold light source instead of thermal light source is not far away, so we can regard LED as a cold light source.
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