I switched from a Tek light T-5 to a Kessel LED last year and wouldn't go back just because I hated spending money on bulbs.
When we talk about LEDs, in my opinion the problem isn't that they do not promote photosynthesis as well as a halide/T5. As Dr. Sanjay Joshi said "a photon is a photon""... the problem is that they miss parts of the spectrum that are needed for reasons outside of photosynthesis. For example, it has always bothered me that the LED spectrum ends at 660 nm for most fixtures. I don't believe Cree or Phillips has an emitter above 660 nm, and if they do, it isn't in any mainstream aquarium fixture. Red light above 660 nm has long been known to play a critical role in the development of terrestrial plants. For example, the wavelength of light signals for "phototropism" - when a plant moves itself in response to changes in light directivity. Some plants are triggered by blue light, others by red.
Does light play non-photosynthetic roles in corals? I don't know for sure. Corals are very different from plants. But I do know for sure that some corals respond to light directivity... I'm sure pretty much every experienced hobbyist would agree. I have noticed Xenia and colt corals seem to "climb" towards light. I'm not an SPS-hobbyist... how do they respond to light directivity?
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