Truth be told I've keep Zoas under ATI t5ho, radium metal halides on m80 ballasts, and under LEDs (ocean revive + buildmyled). So far it has been linear. I had very poor Zoa growth and polyp size under the t5ho (but the best acropora growth and color), metal halides improved both growth and size, and since changing to LEDs they're really exploding now. Granted...this could also be due to the fact that these light changes happened over 3 years so my experience level has increased as well as tank maturity. Probably a little of everything has caused the improvement