You can reduce the light intensity by raising the light further from the water. The disadvantage of this is that more light spills out to light up the room. I have yet to see a usable method for determining how much reduction you get by raising the light one inch, two inches, etc. With poor or no reflectors you can be pretty safe assuming the intensity is proportional to the distance between the plants and the light, but in a 20 inch deep tank, with tall plants as well as carpet plants, I don't see a way to use that method.