The first purpose of red light on headlamps and handheld flashlights is to preserve and improve night vision. Military service members often work in the dark, when the sun is down. Sometimes, the moon is dim. So, it is not a reliable source of light.

Why do you use a red light at night?

It takes a very low light level sensed by the eyes to produce this chemical called rhodopsin, or visual purple. … It is an interesting trait that deep red lights do not trigger the neutralization of the rhodopsin, so astronomers and safety officials use red lights for night lighting to allow night vision to continue.

Why do spies use red flashlights?

When exposed to normal light, your eyes would adjust to the light and end up being less adjusted to the dark and you wouldn’t be able to see in the dark as well. Incidentally, it can be any color. Red is just kind of traditional.