hi dinocol,
the opposite will happen in a larger time frame: the led decreases the output slightly in a few hundred hours of runtime. and the second spectral peak on "yellow" wavelenghts is decreasing because the flouroscent dye is bleaching out (theoretically).
there is no burn in known for my person as watchable on cold cathode flouroscent tubes, and this happens in one or two minues after each start of operation.
hope, this could help you,
torsten
