Put the light as close to the plants as possible with out it burning them. It looks like you have an air cooled hood so you should be able to get them pretty close. A suggestion I have for you is to invest in t8 lights they are $10 for a 2 bulb setup at wal-mart. you can put that right on the plants, I mean that literally. This will also save you a shit load of money on your electric bill too.