Bright white light is good? I thought warm light is best
During the day, bright white light feels good, but at night, warm light is more comfortable. I think the most important criteria is the overall amount of light in terms of lux, how bright your environment is. For example an overcast day is around 1000 lux while a typical room is 50-100 lux. A sunny day outside is 10000-20000 lux.
Basically, the idea is to make your room as bright as possible, in the most efficient way you can. We're trying to artificially recreate long summer days, when the restorative processes of the body are at their peak. Incandescent is always the best choice, fuller spectrum, but running 4 x 250W 18hours a day is going to be massively expensive.