Image intensifiers or residual light amplifiers are electronic components that amplify images of low light intensity so that the viewer can recognize the images. They are used wherever there is insufficient illuminance to view images.
Image intensifiers are used at the lowest illuminance levels of less than 0.1 lux( lx). In principle, they are electron tubes with an input phosphor screen, a focusing and accelerating system for the electron beam, and a small photocathode for image display. The incident image falls on the input phosphor screen, which is formed by a photocathode. The electrons released from the cathode are accelerated by high voltage and focused in the focusing system. The focused electron beam hits a phosphor layer on which the image is reduced in size and displayed in focus. High- sensitivity CCD sensors are an alternative for image reproduction.