I have discovered that a Sun Lamp gives better medical-success-chance because it emits 100% light instead of 50% as Standing Lamps & Torches do.
However, the Sun Lamp turns off at night and there is no way whatsoever to turn it on again at night.
This "Medical Lamp" would work a bit like a Vitals Monitor, that it stands close to a medical bed(s), and when someone is in that/those bed(s) it is turned on automatically (and turns off when not needed, because the bed is empty).
And of course, it emits 100% light.
It would be a nice medical addition to the base Rimworld game.
This is still a myth, or at least should be. If this actually effects medical chance, pretty sure it is a bug.
Workspeed is 100% down to 50% light, and drops to 80% at 0% light.
Light also effects mood from Darkness debuff.
However, none of the four medical stats are effected by light level. A lamp is all you need.