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2025-02-10
How to distinguish between cold light source and thermal light source? The so-called cold light source is a light source excited by chemical energy, electrical energy, and biological energy, such as fireflies, etc.; the so-called thermal light source is a light source excited by thermal energy, such as incandescent lamps, etc. So, is the standard light source a cold light source or a thermal light source? The following will answer your questions.
Cold light source
Cold light sources are luminous light sources that contain almost no infrared spectrum. For example, the popular LED light source is a typical cold light source. Cold light sources are light sources excited by chemical energy, electrical energy, and biological energy (fireflies, neon lights, etc.). They have very good light sources and flicker characteristics.
The characteristic of cold light source is that it converts almost all other energy into visible light, and there is very little light of other wavelengths. However, thermal light source is different. In addition to visible light, there is also a large amount of infrared light, and a considerable part of the energy is converted into infrared light that does not contribute to lighting. The light emitted by the thermal light source after adding an infrared filter should be similar to the light emitted by the cold light source, because the infrared light has been filtered out.
Therefore, cold light source can be regarded as a more energy-saving light source, which can convert light energy more efficiently.
Thermal light sources are light sources that are excited by thermal energy. Such as incandescent lamps, halogen tungsten lamps, etc. Incandescent lamps emit light through thermal radiation, with 80-90% of the energy converted into thermal energy and about 10% of the energy converted into light energy. Incandescent lamps are a typical process of converting electrical energy into thermal energy, and then converting thermal energy into light energy. The thermal energy loss is high, so the luminous efficiency is low. Fluorescent lamps emit electrons through the filament, which collide with the inert gas (filled in the lamp tube) to ionize, and mercury is liquefied into mercury vapor. Under the impact of electrons and the electric field at both ends, mercury ions are ionized in large quantities, and the movement of positive and negative ions forms gas discharge, that is, arc discharge, while releasing energy and generating ultraviolet rays. After the phosphor on the inner wall of the glass tube absorbs the energy of ultraviolet rays, it is excited and emits visible light.
Simply put, a thermal light source releases a lot of heat while releasing light energy. The tungsten filament lamp we used to use is a typical thermal light source. After using it for a period of time, the bulb will become very hot.
Thermal light source
1. Different meanings
Cold light source is a light source excited by chemical energy, electrical energy, and biological energy. It has excellent light source and flickering characteristics. When an object emits light, its temperature will not be higher than the ambient temperature. This kind of light is called cold light, and we call this light source cold light.
Thermal light sources are light sources excited by thermal energy. For example, incandescent lamps, halogen tungsten lamps, etc. Incandescent lamps generate heat, 80-90% of the energy is converted into thermal energy, and about 10% of the energy is converted into light energy. Incandescent lamps are a typical process of converting electrical energy into thermal energy, and then converting thermal energy into light energy.
2. Different characteristics
Cold light sources convert almost all other energy into visible light, with very little light of other wavelengths. Hot light sources are different. In addition to visible light, there is also a large amount of infrared light, and a considerable part of the energy is converted into infrared light that does not contribute to lighting.
A light source that is stimulated by chemical energy, electrical energy, or biological energy is called a cold light source; a light source that uses the principle of heating an object to produce light radiation is called a thermal light source.
It should be noted that cold light sources do not generate no heat, but their light emission is not converted from heat energy into light energy.
For example, LED light source is a typical cold light source. The core part of LED light source is a chip composed of p-type semiconductor and n-type semiconductor. There is a transition layer between p-type semiconductor and n-type semiconductor, which is called pn junction. In the pn junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thereby directly converting electrical energy into light energy. This is the luminescence principle of LED light source.
The incandescent lamp is a typical thermal light source. It first converts electrical energy into thermal energy. After the filament is heated to an extremely high temperature, the electrons outside the nuclei of the elements that make up the filament material will be excited, causing them to jump to the outer layer with higher energy. When the electrons jump to the lower-energy electron layer again, the excess energy is presented in the form of light, completing the conversion of thermal energy into light energy.
Therefore, we cannot simply distinguish between cold and hot light sources by the high or low external temperature of the lamp. A cold light source does not mean that it does not generate heat. To distinguish between cold and hot light sources, we must understand the principle of light emission and see whether light radiation is generated by heating up the object.
Standard light source
Standard light source is an artificial light source for color matching. It specifies color temperature, color rendering, illumination and environmental requirements. Whether it is a cold light source or a hot light source does not actually affect it. Of course, there is a trend that cold light sources are replacing hot light sources.
After all, the history of the development of artificial light sources is to continuously improve efficiency, and the use of more energy-saving, environmentally friendly and efficient cold light sources has gradually become the mainstream.
In the past, most standard light boxes used fluorescent lamps and incandescent lamps. However, with the continuous development of LED lamps, mainstream color matching light boxes have begun to use LED lamps. With the continuous upgrading of lighting technology, the era of cheaper and higher-quality LED standard light sources will come.
D65 light source is the most commonly used artificial daylight among standard light sources, and its color temperature is 6500 K. The D65 light source in the standard light source box simulates artificial daylight, ensuring that when observing the color effect of objects indoors or on rainy days, there is a lighting effect similar to that observed under sunlight.
D65 light source only has requirements for the spectral power distribution of the light source. Generally speaking, the two most important indicators for judging D65 light source are color temperature and color rendering index. There is no regulation on whether it is a cold light source or a hot light source.
CIE has not yet recommended a corresponding standard light source, so the simulation of standard illuminant D has become one of the important topics in current light source research. Currently, there are three types of artificial light sources that simulate the D65 standard illuminant: high-pressure xenon lamps with filters, incandescent lamps with filters, and fluorescent lamps with filters; among them, high-pressure xenon lamps with filters have the best effect in simulating D65 illuminants.
With the continuous development of lighting technology, many D65 lamps now have LED lamps. The more popular LED light source is a typical cold light source.
