Dimmed, I even bought a mood light from Overstock.com that can change colors too, it acts like a bright night light which I also use it as from time to time to not step on my cat who likes to sleep right where I step when I get out of bed.
I like it all ways, regular light, dim light, no light, daylight... But, I have very sensitive eyes & if this is a long session, or if there is a chance we're going to nap or sleep after, I then prefer dimming the light. I think the only light I DON'T like is fluorescent, because it's unattractive & it gives me a headache!
It all depends on the mood--sometimes lights off can be fun, causing you to focus on other senses; sometimes lights on at normal brightness is good for a change; but in general, dimmed lighting, especially candlelight, is the most mood-setting for me.