There is no such thing as too much lighting for an aquarium. If you could somehow take every metal halide in the world and put it over a reef tank, it still would not equal the intensity that the sun offers over the reef in the ocean.
The problem with hobbyists is that they misunderstand the organisms they are keeping. For example, say you have spent the entire winter indoors. When spring finally rolls around with its intense rays of sunlight, you decide to do some gardening for eight hours starting at 9am. Of course you are going to get a very severe sunburn.
The same is true with marine organisms. You can't just take a coral or anemone that has been under inadequate lights at the lfs, and put them at the top of your liverock formation under intense MH light. You have to acclimate them to light just as you acclimate critters to water parameters.
Another frequent mistake made by hobbyists is killing thier livestock with oxygen poisoning. Why is he talking about oxygen poisoning in a lighting thread?!? I'll tell you. The algae that lives in the tissues of anemones and some corals is part of a symbiotic relationship. The anemones/coral provides the stable envoronment and the "home", while the algae undergoes photosynthesis and shares the beneficial byproducts. The problem arises when you take a coral/anemones that his been in inadequate lfs lighting and expose it to intense lighting....
The algae undergo a "bloom" within the anemone/coral and produce so much oxygen bypoduct that it kills the host organism.
Too much lighting? A myth. Too much lighting too quickly? A reality