Should be enough, if you have brown porites.
Mine are close to the top, under 110W PC, 20g long tank (12" depth).
If the other color - really don't know. Still have a problem with finding the suitable conditions for the fine beige Xmas tree rock and the green one, with wine red worms. Asked at sps forum - they have the same problem with green porites, even under much better light.
