Night vision cameras are used in many applications like in spying robots and also for surveillance purpose. Like any normal camera, they too require illumination for their operation.. But for cameras used in surveillance purpose that are used mostly at night we cannot rely on visible light. In some cases this visible light can be amplified, but these cameras are not reliable and cannot be used at places where there is no light at all. For this purpose, another part of spectrum of light is used, that is the Infrared band. Some of the cameras makes use of the fact that all warm bodies radiate infrared light.
3 techniques to attain night Vision for these cameras
Thermal Imaging: These techniques are based on the fact that all the objects illuminate infrared light. The infrared radiation from all the objects is collected and an electronic image is formed. Normally semiconductor devices involving Mercury Cadmium Telluride and Indium antimonite are used as infrared detectors. They can operate at low temperatures or at room temperature. These techniques basically use the thermal IR part of the Infrared spectrum which involves the wavelength range from 3 microns to 30 microns. They involve use of active illuminators, which emit infra red light on its own.
Low Light Imaging: These techniques involve the use of normal visible light and the basic principle involves amplifying the available visible light to increase its intensity. Some of the low imaging technique involves use of built in chips in cameras where the current generated due to light is constantly amplified.
Infrared Illumination: These techniques involve use of devices which can emit infrared light. An IR Illuminator works on the fact that all warm objects emit infrared radiation. Infra red band occupy a bandwidth besides the visible red band.
Approximate range of IR band is 430THz to 300GHz. Passive Illuminator is the one which produces IR light by reflection or refraction of IR rays from another source. These techniques use the near infrared part of the Infrared spectrum which involves wavelength range from 0.7 to 1.3 microns.
Advantages of IR illumination method for night vision cameras
1. They are not affected by surrounding light.
2. They are inexpensive.
3. The cameras using IR illuminators have good sensitivity
4. IR LEDs specifically have lower consumption rate and longer lifetime.
5. It is possible to take pictures at night time without disturbing the environment.