Originally Posted by Ingy
Yes and no. I don't want to overly complicate the issue at hand. However someone said corals need PAR and not specific colour. That is incorrect as corals need a specific range of PAR, specifically that in the blue range of light. Yes that is starting to describe PUR, but that will just confuse people.
Corals want PAR light in the 420 - 500nm range (blue-purpleish).
What would your PAR meter say if I supplied a very bright ORANGE light (680nm say). the PAR meter would read a significant PAR value if it measures all PAR light. But your coral would shrivil up and die as not enough PUR value for the specific photosynthetic bacteria. And those orange lights are very popular for growing plants.
So all that to say to the OP, PAR values are a very good indication as long as the light is designed for the application. Actinic light IS what your corals want. The white light is so WE can see all the pretty colours.
I am almost positive a coral grown under a warmer light would not shrivel up and die, it would just be browner. Corals in very shallow reefs are not getting the complete blue spectrum that deepwater corals get. Yes a deepwater coral will thrive from bluer lighting but a shallow water coral will do better with a full spectrum light. Corals zooxanthellae use a wide spectrum of light not just the 420-500 nm range. Hence the reason people use warmer lights. For example, someone running 2 of the same exact fixture with different bulb colors over 2 sides of heir tank. Te side with the cooler blue color will have better color but not as fast of growth while the warmer color will have faster growth but not as great color.