You dont have a light meter ? Umol reader?Yup, did it a couple days ago. I'm just seeing how close I can get with it now in the new space. I have 4 x 60W equivalent CFLs shining on it, if that gives you any ideas for a recommended distance from the plants... the budding ones now are loving it with them 15cm to the side. I just occasionally rearrange them to share the light.