Someone asked for some suggestions about what color he should choose to back-light his truck's instrument panel. I was a bit bored at the moment and had just finished my first cup of Joe.
I haven't done it, but perhaps I could shed a little light on the subject from my Armee flying days (Pun intended!)
Early on the military used red lighting for night illumination of local scenes. That included things like your tent, a cockpit, a vehicle dash, or anything exposed to "the outside"...Like the interior of a submarine that has surfaced and has a hatch open to the sky (Subject to aerial observation.)
The red light provides ample illumination for most tasks, but not tasks requiring attention to detail.
Instruments designed for use at night, in tactical aircraft in the bygone era before NVD's were marked boldly. Limits were big blocks or hash marks or the like so that when scanned could quickly tell you if you were good or not so much. Again, sort of in the macro. Either I was over-temping an engine or I was not. But could I tell you the exhaust stream temp? Probably not likely. I could tell you, "It went over 843C for three seconds...But not that it touched 900C for a second.
Further studies of redlight usage noted that it would not interfere with the natural production of a chemical called Rhodopsin (Visual purple) within the eye itself. That caused the cone cells to become active. Further studies also taught the army of the 70's that red light also causes a degree of anxiety, as it is often associated in our minds with bad things like your tank is on fire, or the flash of a muzzle, and other things like that.
Conversely, the use of a narrow band of bluish-green light which was discovered to have no effect at all on night vision devices had none of the bad effects associated with glaring red hues. That same band of bluish-green light also has no negative effect on the Rhodopsin in your eyes. Now in a civil and urban driving environment, white light, commonly found overhead almost everywhere will wash out Rhodopsin immediately.
Something about this rhodopsin. It takes your eyes 30-45 minutes to generate enough rhodopsin to fully stimulate the mass of Cone cells located all around the fovea-centralis where night vision develops. This is what is commonly referred to as dark or night adapting. If you are exposed to a strong white or red light, you are back to square one and it will take (depending on the magnitude of the exposure), another 5-45 minutes to re-adapt to the dark.
Now the cool thing about using only blue-green light, even in flashlight bulbs is that you can enjoy full night vision and full daylight vision at the same time. Night vision images are only seen in shades of gray. Day vision, however, can occur in 16 million different colors in a human eyeball. You actually have very good night vision depending on the available ambient lighting, so if you had all blue-green dash lighting you could read things like your EGT or a name place on a map in great detail
Finally, People driving cars with red dash lights are angry people, while people driving whose interiors are illuminated with blue-green lights are happy. The only exception is the person driving a car whose interior:
1. Is illuminated with a lot of blue-green light
2. And within that interior, you also have Hilliary seated close by.
In this rare instance, it is better to go to total black out drive while having taped one's face with layers of quality duct tape.
Most of the above are true...
