Right which is why I say it will screw with their contrast.
I say this because someone I know who is colorblind can't use a red headlamp when outdoors. A lot of people use red lights to preserve their night vision, but for this person they can't see clearly with it vs. a white light.
Didn’t know this before either, but it seems a common type of colorblindness, protanopia, results from a general insensitivity to red light and also hinders distinguishing between reds and blacks.
Small nitpick, I think people use red headlamps to preserve other peoples night vision not their own. Or am I getting that wrong? Wouldn't white light work just as well or even better for for one’s own "vision at night"?
No, red headlamps help the wearer too. Red light triggers less of an adaptation [1] response than other hues relative to the amount of useful illumination they provide. Red light lets us perceive our surroundings, but doesn't trigger our eyes to close the pupils and become less sensitive to the incoming light.
(Blue has the opposite effect, which is why a room lit only by blue light can feel both dim [hard to see] and harsh [unpleasantly bright] at the same time.)
You're correct, and the other responses saying otherwise are misinformed. Protanopes do not have long-wavelength cones and thus have reduced sensitivity to that end of the visible spectrum, i.e., red light appears dimmer to such individuals. This is also why red on black (or vice versa) is a color combination with poor accessibility, since it has reduced contrast for protanopes as the red appears darker and thus closer to black.
