I use a PAR meter with mine. If you don't have one, your local club might be able to loan one (if you're a member - ours does). You might even be able to rent one from some of the vendors on this site.
Base your PAR target range on the types of coral and their locations.
Cheers,
Ray
Here's a handy reference from SenEye you could use as a "rule of thumb" for most coral, and you could use the guidelines for anemone and you should be fine.
What PAR and kelvin do your aquarium corals need to thrive? Find out on our simple marine reef chart as a quick guide...
answers.seneye.com
In my experience, most mushrooms would be okay with quite a bit less than most stony coral. The zoanthids can do fine in lower light levels as well, but I have some of both in my frag system that are basking around 300-350 PAR, and loving it.
Cheers,
Ray
Mushrooms can tolerate a wide range of light. I have some in my tank getting less than 100 par and others getting north of 600 par. Same species. They look no different either way. My propagation box is getting about 250-300 par
I think it depends on the "mushroom" - my Actinodiscus sp. (reds, greens, blues) definitely crowd around the fringe of the reef, with those that have drifted into the open visibly shrinking away from the 250-300 PAR on the floor of the aquarium, and those in the edges (more in the shade) basking in reflected light appear wide open. I guess everyone's mileage varies with'em. So mebbe we're sayin' give it a shot and see what the critters have to say about it - no hard and fast "rules" with them.
Cheers,
Ray