Red is the traditional colour to maintain your "night vision".
> Many headlamps etc have extra red LED's for a night vision mode.
> But which colour is most efficient at low currents at night, I don't
> know.
This is true. OTOH, green or greenish-yellow is the color to which the human eye is most sensitive. AIUI red is good in that your pupils don't tend to react much, but green should be easier to see.
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This is correct. You can stay dark adapted with quite high levels of long wavelength red light and it is still used for that purpose. But many people find it hard to focus their eyes and a strain to read instruments or maps in red light. Increasingly low levels of green and since they are available white LEDs are used at low intensity for this purpose. If the light is dim enough it doesn't matter what colour it is - you don't see colours in scotopic vision only the brightness.
BTW peak rod sensitivity is 510nm I misremembered. And you can see how rods barely respond to red light with wavelengths longer than 600nm so you can use lots of that with almost no effect on dark adapted night vision. The red cones do respond to it. But chormatic abberation in the eye can be a nuisance for fine work or reading.
Regards, Martin Brown
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