I have a new 40G long aquarium, but no lights yet. I thought the lighting fixtures in the stores like Petsmart etc. would have 2 slots for bulbs, but they only have one. Is there any advantage to getting 2 smaller fixtures, side by side, and using 2 different light bulbs, one for plants and one for ambience? It's a bit more expensive doing it that way, but I don't want to be buying a bunch of different hoods because I can't make up my mind. Advice appreciated.