Hahahaaa! My first thought was "Isle of" but it didn't work at all.
Yeah, that's not a cryptic clue, but it was cute.
So how could we fix it? How about...
Main man's surroundings (5,3)
The moon is actually more useful than the sun since the moon gives us light at night when it's dark. The sun only gives us light during the day when it's already bright out.