20 inches deep, 30 inches wide, and 5.0 feet tall... so i dont know lets just say 2 by 3 feet so I have 6 square feet. The number of inches I can get my hps off the top of my plants fluxuates with how cold the air from outside is.. today it was kinda chilly so I managed to get the light about 10 inches off the tops.. about a foot on average. But I have no reflector or anything the bulb is simply exposed.. so tons of light is bouncing all around where it isn't being used. The inside is painted with clean coat of flat white paint and when you close the door hardly any light seeps through... I need to brush up on these lighting laws I think I freaked out for no reason.. because let's see If i have 6 square feet and the horilux has somewhere around 55,000 lemuns that means I have a bit more then 7,000 lumens a square foot.. but does it matter that it's bouncing all around in 30 cubic feet of space? I dont know.. turtle help me! Am I good??