SV: ATM - Color sensitivity of the eye

["Nils Olof Carlin" <nilsolof.carlin@swipnet.se>]

Jim McKay asked:
> 
> Is it the case that red light represents the best choice for preserving
> night vision?  Has anyone used other color of light ?  If so, are other
> wavelengths better at illuminating objects without destroying night
vision?
> 
If you look at light sensitivity curves for rods and cones (try Clark:
Visual Astronomy of the Deep Sky, page 9), you find that for light above
650 nm, the difference between rod and cone sensitivity is least, that is
red light. What we want is the least disturbance of rod dark adaptation for
the least light that is enough to e.g. read star charts by. Red should be
best (unless visual acuity is very much higher for cones at another
wavelength, thus allowing reading by very much dimmer light. I have no
reason to believe it is so). Clark himself says "...the rod cells are more
sensitive to *all* colors than cone cells so there is no advantage to using
red light". This argument doesn't take in account that the difference is
very highly colour-dependent.

This quotation is from Brian Skiff: "Red lights are best, but if you can
see that it's red on the paper you're looking at, it's too bright".

Nils Olof