I have seen plants that get to much light.. they will turn white on top.. much different than a burn.. they can recover from "to much light" very easily... this can happen outdoors at high elevations... or if you are running a bunch of hps real close to one another... ie 3000watts in 4x6 area...

but I have not seen burns or over lighting from flor's.... not even when the lights are sitting right on top of clones... seems fine...