I'm not a table mechanic, but in my experience, it will really come down to type, size, wattage (to a degree) and shape of bulb in the shade. Task lighting vs accent, spot lights vs flood. Though there is importance to illuminating correct color, obviously the major objective is to eliminate shadow... shadow not only cast by the balls, but by the rails. The best way to do this is to build or buy a lamp system employing parabolic reflective grids like those sold by Diamond Billiards. But distance from the surface remains vital for the shadow-free goal. There's nothing more annoying to an avid pool player than trying to find the edge of a ball hidden in the dark.