I just started growing under flourescents in June. If they are hight light orchids, I put them an inch or two from the lights. Any closer, I think they would burn. Medium light orchids I put about 6 inches away, and low light orchids about 12 inches away. But I am just a newbie, maybe somebody with more experience will chime in. So far they are growing. Now, I just have to get them to bloom!