Red Filter Green Filter colored light fits flashlight not harm night vision
Red light is most often used to enhance, or more properly, not harm night vision. Red light provides great contrast and is not visible to the human eye over long distances. It also works well with night vision scopes and goggles. Photographers use red colored light when doing night-time photography because it provides contrast while preserving the natural shadows developed by darkness. Red light cuts through smoke better than white light and, with the exception of red lines and marks on maps and charts, it makes reading in low, or no, light possible. Police and military units like the red LED for night operations because it will not interfere with night vision technology and cannot easily be picked up by other people.
Green light is preferred by hunters and fishermen because it is a very soft light that will not spook their prey. Green also does not attract insects like white or yellow light does. It is not easily picked up, unless looking directly at it, so it is useful in covert operations. It is also useful in smoke or fog filled environments. Green is also very popular for night time map reading.