I think I have seen 9 watt CFL bulbs ("40 watt equivalent") That should drop the light intensity enough to do without CO2. But, if those little reflectors are not polished aluminum on the inside, the 13 watt bulbs may be just right. The chart was based on a polished aluminum reflector, I think.
Hoppy, my planted tank light guru
, the reflectors appears to be plastic with chrome finish (aluminum like). I tapped on it, sounds more like plastic than aluminum to me. Will that qualify as "aluminum reflector"? So then does that make my current light just right or still would be better off to downgrade?
Underside of the light: