With mine personally, back when I had 4 bulb, I never felt it was enough to get the colors to pop. They thrived, but when I first bought it, the color was so much nicer. Seeing they usually are put lower in aquariums, I came to realize 4 bulb was really only enough to keep them thriving, but not enough to enjoy the colors they can hide. And then I noticed when I got my 6 bulb, the growth rate increased, and the eyes glowed much brighter and finally had the same colors as I first got them for the lfs. The 4 bulb made it look brownish. The 6 bulb brought out hidden colors, even when placed close to sand which most of mine are. Granted, it's not mandatory, but to get the colors to pop, 6 will help out alot especially on chalices where the eyes can be so little