Internet research can be very frustrating. More than half the time we are reading something from a very vocal but relatively inexperienced hobbyist who is often simply passing along something he heard from some other relatively inexperienced hobbyist.

Don't be fooled by product marketing hype about PAR.

Don't be fooled by what some expert or scientist says about proper PAR for coral. Everything is relative to 1) the situation, 2) the conditions of a particular experiment/study and especially 3) that expert/scientists own limited knowledge at the time.

From what I've read and what I've experienced, PAR meter values seem to be inappropriate for LED's. The PAR meter manufacturers actually publish how to use their meter for LED light but then make a disclaimer that such readings are not definitive. I believe it's partly because of the narrow bandwidth emissions of LED's that make the light unreadable. It's my understanding that a PAR meter is made to measure a value by reading emissions across a complete spectrum. I wouldn't get caught up with PAR.

Instead, I would take a practical approach. I have always recommended that we run our tanks by watching coral response/behavior. I'm not saying not to do testing, just that many variables can be seen in coral behavior. For instance, it's coral response that tells us the general Nitrate level, low or high. PO4 level can also be seen in coral response. We can judge when a tank has not been using AC for too long and lighting can be judged in a similar manner.

I would start LED's at low intensity and turn them up 10% every 2 weeks watching how the coral respond, watching the change in algae growth while taking into account other variables in the water like Temp, SG, Alk, Ca, and even turbidity. For example, when AC is used, it can clarify the water by as much as 25%, making lighting intensity 25% brighter to the corals.

Hope this helps rather than confuse.

Aloha,

Mark 

Normally Yes, but when it comes to light overexposure the response is delayed, similar to people playing all day, having fun at the beach without thought of sunscreen. The bad effects of coral sunburn can take several days to start showing up and, depending on the severity, it may be 2 weeks before the coral dies. If it doesn't die it can take a month or more to fully recover. 

One key is to protect from UV radiation.

Aloha,

Mark