Mellow they make 2 Hortilux bulbs. One is an HPS bulb...again this is a great bulb and should do a fantastic job for you. THe other is a MH Blue Hortilux bulb. Just has a much more balanced spectrum so that you get a much higher blue spectrum than with the HPS Hortilux but with all the same reds and oranges in the regular Hortilux. Either is great but if you have a MH light already then Blue Hortilux would be the way to go. But the regular Hortilux is still superior to any other HPS bulb on the market