On the issue of rods and cones the sensitivities of each differs with respect to different wavelengths of light. Fortunately rods arent very red sensitive (nor blue either really) which means red lights are good for not wrecking night vision. I'm told that bomber aircraft in one of the world wars used to use blue lights for a similar reason - but the red should be better for preserving night vision from the spectrum of the rods.
http://en.wikipedia.org/wiki/Purkinje_effect
cones spectral response
http://en.wikipedia.org/wiki/Cone_cell
Rods spectral response
http://en.wikipedia.org/wiki/Scotopic_vision
Cheers,
David