not trying to start a fight or anything.. but i tend to dissagree....
granted he's right the spectrum is the key to the problem... but MH and HPS are all made the same,
the gas content in side the bulb is what makes the specturm change.
a GE 400watt MH will give you a white, color,,,,, if you where to guage it, it would be somehwere about 10,000k kelvin......
what goes on here, is the people who make fish tank bulbs change the % of gas's in the bulb (thats what changes the color)
Im not sure what the gas is, probly something like agon, or helium or something like that......
IMO i would just go get the right stuff now.... insted of finding out later that it didnt work.....
my sump will be powerd but a 400watt MH from sungrow system... its a mogal bulb
check this out...
http://en.wikipedia.org/wiki/Mogul_lamp
read up on bulbs..... you will find that meny people are fool'd by the gimick of your LFS... LOL that sounds funny..
ill let you know how that works