When I take my light meter and measure sunlight intensity at noon on a clear summer day-----around 10,000 fc (footcandles). That's true wheather standing atop a tall building or on the ground.

18" directly below my hortilux 1K hps is also 10,000 fc------now another 18" farther below is only around 2500 fc-------yep about 1/4 from the previous point of measurement.

And yes Virginia----I've found that plant material exposed to intensities much higher than 10K fc start bleaching-------and not from heat.

So what this means to me is-------we have a very small envelope of useable light intensity from HID lighting.

Things to do:
1) keep your canopy flat or concave with tying branching down, trellising, or whatever.
2)light movers are great----- especially in the aero/hydro world where moving plants around is not practical.

cheers,

Alaric