I used to run it 12 hours at 192w. Now I run it at 96w, with the exception of having a 3-4 hour period (mid-day) of 192w. The way I see it (and this is NOT science here
), I've reduced total light intensity by over 40%.
Here's the "math"
192w x 12 hours = 2304
(96w x 6 hours)+(192w x 4 hours) = 1344
My theory (based on natural observation - not science) is that even "high light" plants only need high intensity for a brief period to do well. Furthermore, these plants don't benefit from a long period of high intensity light.....BUT, "low light" plants can and do suffer from too much light.
My local plant club did an experiment re: photoperiod. We set up equal aquaria with equal fauna (common plants - hygro, hairgrass, ludwigia, etc) and set them on different photoperiods - 6 hours, 16 hours, and 24 hours. Lighting was done using flourescent coil bulbs at an intensity of about "4wpg".
6 hours - plants flouished, grew, and soak up nutrients - very little algae
16 hours - plants suffered, green water and thread algae flouished - modest nutrient uptake
24 hours - plants died, green water struggled - increase nutrient load (dying material).
In my very humble opinion, a LOT of algae problems stem from too much light. Too intense for too long. Light should ALWAYS be the limiting factor.
whew....where did all that come from?