Traditional Night Vision
Traditional night vision, also known as NVDs (night vision devices) or green vision, use an optics based system to pick up small traces of ambient light. This light is filtered through an image intensifier tube. The light is then amplified allowing something normally imperceptible to the human eye to become visible.
There are a few limitation to this kind of night vision. Because it amplifies ambient light there must be a certain amount of light present. Traditional night vision is hindered in extreme low light and low visibility situations.