indoors greenhouse for winter

[jcaballero]

I had plans to build a greenhouse this summer, but to heat the greenhouse is going to be pretty expensive. So, I decided to make a 6'h x 5'l x 2'd shelving system with 2 shelves, 3 (175 watts) MH lights, fan and humidity trays. Since it's going to be inside the house, I won't have any problems regulating the temp.I'm thinking about keeping the orchids 2-3 ft away from the lights. The 2nd shelf will hold less light demanding orchids and I'll use fluorescent lights
I'm debating wether to use all 3 MH or just 2 MH. What do you think I should do?