Infrared thermography is the use of optoelectronic technology to detect the infrared specific wavelength signal of an object's thermal radiation and convert the signal into images and graphics that can be distinguished by human vision, which in turn allows the calculation of temperature values. Infrared thermography allows humans to transcend visual barriers and enables people to see the temperature distribution of an object's surface.

　　Everything in nature, as long as its temperature is higher than the temperature (-273), there will be irregular movements of molecules and atoms, and its surface will constantly radiate infrared rays that cannot be seen by the human eye. Its working principle is that it receives infrared rays from objects and displays the temperature distribution on the surface of the object under test through a colorful picture, thus forming a readable image; its core is a thermal imaging camera, which is a sensor that can detect small temperature differences and convert the temperature difference into a real-time video image for display. But you can only see the thermal profile of people and objects, but not the true nature of the object. Thermal imaging cameras can penetrate rain and fog, and they can still display images even in dark environments. However, the heart of a thermal imaging camera lies in its sensor. However, due to technical limitations, there are not many well-made products and the price is high. In addition, its images do not reflect the color and detailed appearance of the surveillance scene, so it is not suitable for regular applications. Moreover, thermal imaging cameras are difficult to image through glass and can be obscured by transparent objects, which also affects its further application.

　　Visible light supplemental surveillance is to add a visible light source to the monitored scene so that the surveillance equipment can capture clear and colorful images. However, this application method is clumsy and requires the addition of sufficient light sources in the monitored scene to ensure the quality of the colorful images. Energy consumption and cost are large, except for city road monitoring street light source, this method is rarely used in other scenes.

　　Laser / infrared light fill light surveillance is the fill light source is installed on the camera as part of the camera. This is currently a widely used method of night surveillance. And there are two types of fill light technology: laser and infrared.

　　Laser fill light means that the camera is equipped with a laser light source, laser using spot uniformity enhancement technology and spot auto-focus technology. With the advantages of strong luminosity, more uniform picture, less power consumption, longer service life. The laser light for security is almost all laser manufacturers' products, supporting the more passive.

　　The market mainly uses infrared light-emitting diodes, light emitting body consists of infrared light-emitting diode matrix; emission wavelength of 850nm and 940nm infrared LED is the mainstream application. Infrared light supplementation technology is worried about the life of the infrared lamp. The current main solution is to make the infrared emitting diode with infrared radiation efficiency of the material (commonly used GaAs gallium arsenide) into a PN junction, plus forward bias voltage to inject current into the PN junction to excite infrared light, can achieve low red burst, or even no red burst, long service life.