A red light is used to acclimatise the eyes to dark light conditions. When I was in the forces- we used to have 30 minutes in a dim red light before going out on night patrol. To actually see with a red light- Unless it is infra-red and you have the infra-red goggles is impossible. I now ride offroad and have used a variety of "Colours" of light. The best I have used so far is a Blueish lamp. But do not use it with a yellow lens on your goggles as it turns it Green which is the colour of The countryside and shadows get lost.