How does the night vision work?
Night vision optics use all available light both visible and non-visible to create an image. Light is gathered by the objective lens and focused on a photocathode. This cathode emits electrons when exposed to the light which are then given a high-energy charge by the power supply. The electrons are accelerated through a vacuum inside the image intensifier tube and strike a TV-like green phosphor screen reproducing the image. Since the phosphor screen emits this light in exactly the same pattern and degrees of intensity as the light that is collected by the objective lens, the bright night-time image you see in the eyepiece corresponds precisely to the outside scene you are viewing. The image is being focused and magnified by the eyepiece. The phosphor screen is green because human eye is more sensitive to different shades of green, it is also the color that contributes the least to eye fatigue.
