While perhaps it's arguable if there is a thing as 'too much' light, you certainly can 'shock' corals by introducing them to too much light too quickly. Much like fish need acclimated to different systems, if the difference in light is that great, say going from PC's to 250w+ mh's, the corals need acclimated to the new light. Start the corals at the very bottom of the tank and slowly work them up over time.