Alright, ive just been wonderin this for a while. My flower box is going to be 4' wide x 5' tall x 2' deep. Im thinking about 4 plants in that area and i had originally planned on CFL's but i think it would probably be cheaper to just get a 400 watt hps to get the job done. Would the heat from the hps be an issue in this tight of a space? what would be some good ideas on venting? thanks
One 400 watt HPS isn't going to cover 4 feet wide. You need to use two 250's. Space them evenly so that the spaces from the wall to the light and between the two lights is even. You should try to have 5 thousand lumens per/sq ft of growing area. Yes, you have to develop some sort of way to ventilate. It'll need it. Closed in, your lights will turn that little space into a very efficient oven.