another thing is because led's point the light strait down or at whatever angle the lenses are, the closer the lights are the smaller the footprint.If the manufacturer says 3 x 3 at 18 inches with 800 umols then at 6 inches the footprint would be somewhere around 1.5 x 1.5 with 1800 umols(just an educated guess).This is why plants will show signs of bleaching, in flower 800 umols is where you want to be give or take, 1800 is way to intense and can cause bleaching as well as stunted growth and smaller nugs, a good sign that your panels are to close is the hairs will actually curl away from the lights and can turn brown prematurely instead of pointing up and staying white. the better quality the diode and size of the diode dictate how close you can have your panel. A panel with 5w diodes will have to be further away then one with 3w diodes and a panel with quality diodes will have to be further away then a panel with cheap no name diodes because they are alot brighter and much more intense.
