"To much lighting?"

Is the setup in question running CO2??

there's three factors in growing plants, Light, nutrients, and C02 if you up the light really high, but the other two stay the same you wont benifit nearly as much as if you were to up the light and also supply supporting levels of nutrients and c02.

Its kinda like a fire you need Oxygen, heat and a combustable source, with an inadiquate amount of any of the 3 the fire will burn smaller and not do very well, but if all three factors arent limited it will burn outta control.