Ron
Right now its about the same as it was with the t5...
Its at the bottom of a 10gal aquarium with the led level with the top
and I'm not so sure the inverse square law is as applicable in this application. For it to apply the area of the light beam has to double as the distance doubles, with concave/parabolic-ish type lenses/reflectors I'm not so sure this still applies.
It comes down to the geometry of the area over which the power spreads out. Let's make it easy for ourselves, and assume the power spreads out equally in all directions, in which case the area is the surface of a sphere Therefore at a distance r from the source, the power P of the source passes through an area 4πr2 - the surface area of a sphere radius r.
I = P/A = P/ 4πr2
so I ∝ 1/r2 (∝ = proportional to)
This is the inverse square part - square because the distance is squared, and inverse because intensity is proportional to one over distance squared.
So maybe its more correct in this application to say the intensity is reduced to 1/4, not when the distance is doubled as much as when the diameter of the beam is doubled. The inverse square law assumes this relationship is linear. The beam spreads at the same rate the distance is increased. Which would not hold true in this application.
ummm maybe, my brain hurts LOLOLOLOL