Hmm. I'm no saltwater person at all, but I'm pretty sure moonlights are perfectly safe. They just can't be your primary lighting. OBVIOUSLY
I just think of them as night lights for my fish. I have them on my FW
tank. And on FW
they do nothing.
But I am a photographer . . . and the blue-ish spectrum that the moonlights give off are no where near actual moonlight. Last time I measured the moon I got 4,600K. Daylight is 5,600K (at Noon in Washington D.C. according to Sony). During sunrise I have measured a 3.8 (3,800K). Sunset and evening climbs up to as high as 9,000K. My moonlights (and any others I have seen) look to be WELL above that. I have never measured them though. I think the moonlight's color are meant to simulate the perceived blue that everybody thinks the moon gives off. But actually the moon is reflected daylight, so it would always be around 5.6K degrees Kelvin. The dust on the moon just lowers it a bit giving you a 4.6 measurement.
I just think moonlights are cool. And back to saltwater, (remember I am NOT a saltwater person) I have heard that the spectrum they give out can be healthy for coral life. I guess it gives them a little bit to use during the night when you don't have your main lights on.