Generally, the wavelength of visible light is 0.4 to 0.7 micrometers, which is the light that the eye can see. The section from 0.7 to 400 microns is infrared. Infrared is the invisible light that is beyond the reach of human eyes. In addition, any object emits thermal radiation infrared light above zero, and a heat-generating object such as a human body emits a larger amount than objects such as houses, trees, and stones.
The camera’s sensor CCD or CMOS, also commonly referred to as “Sensor, is a semiconductor device that converts optical images into digital signals. But what is more powerful than the eyes is that it can sense some invisible light, such as infrared light. The sensor has an indicator sensitivity.It is also called the illuminance value, which is the ability to respond to weak light. The higher the sensitivity, the stronger the ability to sense light, and the stronger the ability to sense infrared.
Since the sensor can sense infrared light, infrared rays in the light also enter the sensor during the day, which causes the overall image to be reddish. Therefore, ordinary cameras have filters on the surface of the sensor to filter out the infrared rays in the light. If the infrared camera is also attached with such a filter, the infrared light that is actively emitted by the night camera infrared light will also be filtered out, causing the infrared light to fail. In order to avoid this situation, high-end infrared cameras are generally equipped with dual filters, that is, open the infrared filter during the day, filter out the infrared rays in the light, turn off the infrared filter at night, and let the fill infrared light enter the image through the lens.
The above is why the infrared camera can be clearly imaged at night when the human eye can’t see it. Depending on the infrared camera sensor, it can sense infrared rays. In the environment with poor nighttime light, infrared light or infrared heat radiation of the object itself can be used to realize night vision. At the same time, double filters are used to ensure that the images in the daytime are not color cast.