Can anyone briefly introduce the principle of using night cameras? I’m very curious why some cameras can still take pictures at night, even if there is no light source, and they can still take very c

Can anyone briefly introduce the principle of using night cameras? I’m very curious why some cameras can still take pictures at night, even if there is no light source, and they can still take very clear pictures.

Infrared camera: night monitoring

Infrared camera technology is divided into passive infrared camera technology and active infrared camera technology. Passive infrared camera technology uses the principle that any object emits infrared light above absolute zero (-273°C). Since the human body and heating objects emit strong infrared light, and other non-heating objects emit very weak red light, night monitoring can be achieved using special infrared cameras. Passive infrared camera technology is not used in night vision systems because the equipment is expensive and cannot reflect the surrounding environment. Active infrared camera technology uses a special "infrared lamp" to artificially generate infrared radiation, which produces infrared light that is invisible to the human eye but can be captured by ordinary cameras. The radiation "illuminates" the scenery and environment, using ordinary low-light CCD black and white cameras or using "daytime cameras". "Color automatically changes to black and white at night" camera or "infrared low-light color camera" to feel the infrared light reflected back from the surrounding environment, thereby realizing night vision function.