the blue spectrum HPS he's referring to is a recent addition to HPS lighting. the only example i have experience with is the Hortilux version. for the 400w, they add a 30w filament of blue spectrum, so you end up with a 430w that works in the same fixture (same deal with other wattages.) precludes the need for switchable ballasts, etc.. provides plenty of overlap in usable spectrum, reduces your bulb purchases, etc. to one type. i think for the 430 hortilux it should be around a $30-40 USD upgrade to a standard output HPS bulb. do your homework..