None, you should never use any lighting, curtains should always be closed with blinds, you should wander round in the dark and just imagine what your comics look like
Personally, mine are in the spare room which is rarely used apart form me, I just use standard lighting and keep the curtains closed to avoid any direct sunlight when I am not in there.
I think reference has been made previously to that amount of time that books spend on walls at conventions without too much issue.
I am sure someone with a better answer will be along shortly...
P.