Each type of coral will react differently but it does boil down to a few basic reasons. As mentioned above corals that do feed will do so in the dark. Also corals that are more light dependant produce oxygen during their photosynthesis process, Naturally they burn that energy off as heat, but with to more light they wont be able to regulate that and thus will end up producing hydrogen peroxide...will we all know is not a good thing to have swimming around in thei tissue. Usually the coral counters that by ejecting its Zoox which is again not a good thing for their health.
Mike