I really dont think you have to worry about light pen.. as you can suround the plants with fluoros. I think there are plenty of valid arguements for the fluoros over the hps. One of the resons that fluoros lack good light penetration is that the defuse the light rather than be from a point source like a hps. But plants like defused like more than point light (comes from our days in the oceans) Thats why most green houses use a defusing film. So you lose penetraion but gain defusion.
I say the real test is grams per watt... we all try to get close to the theretical 1 gram per watt.. but no one can argue that .5 grams per watt isnt bad.. Thats almost a pound off one 400 watt (hps or what ever) Well here is a fluoro grow where he got a little more than .5 grams per watt.. I 've seen others and better one but this is the one I can find.
http://users.lycaeum.org/~npkaye/multishelf.html
Last lumens dont really mean anything. I can give you a 100,000 lumen light that couldn't grow mold, and I can give you a 30 lumen light that can grow the **** out of plants. We need to demand our PAR rating.