LEDS CAN burn the plants too , as well as other lights. The glass panel also gets very hot. Do the simple hand method , place your hand between light and canopy top. If you can't keep your hand there comfortably , then your plants can't either.
When I run LED 18" - 24" is the " normal height range , but I have moved to 8" with out issues. ( I have my vegging autos around 10" ) and they dig it. As they get larger I keep the 18" height.