I have a PAR meter and a 75G tank. I had a 2X54W Tek T5 retro mounted in a canopy 6" above the water's surface with individual parabolic reflectors, when I tested the light I found it to be too high for my liking, so I removed the reflectors and painted the inside of the canopy White. Even with that setup I would say I'm in the medium light category, enough to grow glosso laying down, but not especially fast. Deep into CO2 territory.
It is worth mentioning that I have 2 T5 bulbs that put out 25% less light than the bulbs I'm using now, so not all bulbs are created equal.
I also have a really good T8, on an electronic ballast and that bulb alone puts off 25 par at the substrate, this would be enough for anubus, Java Fern, and no CO2.