I don't have direct experience with the AI 16, but their advertisements state a maximum PAR of 100 at a depth of 24 inches. I assuming the 40 gallon tank is 18" deep, so at the brightest spots on the bottom, you should have sufficient light for Acroporas and certainly at the top. Of course, a lot depends upon the mounting height - too close to the water and you'll have to clean salt spray off. Too high, and light intensity suffers. I've found that, in general, mounting the lamps 7 to 9 inches above the water is a good compromise. Now, with all that said, I'm not a big fan of point source lights. I feel their light distribution patterns limit where light-loving corals can be placed. My 2 cents worth, and I would defer to those with direct experience with these lights.