So I'm going to try plan B for lettuce. My cobs failed, mostly because it was way to much light and too hot for them Here is a start to my new setup. I am just building it out right now.
Going with:
4x8 space
18 - 22w 6500k integrated T5 LED light
9 - 4 inch NFT channels
This will provide me with 108 spots to grow a head of lettuce.
This setup pulls 420 watts at the wall, and 3.7 amps, at 13.125 watts per sf. The lights say 22 watts, but they really pull more like 23.3 watts each. I'm guess there is some overhead in the wiring and such.
As far as cobs go, i'd bet with proper cooling, distance and color, cobs would work fine. Maybe get them at 5000k - 6500k and place them way higher over the lettuce then you would over say tomatoes. If you were running in a 4x4 space with reflective walls, you could run 4 cobs at 50-60 watts each, put them like 3 or 4 feet above canopy. Don't use lenses or reflectors. The problem is you would want to keep the space at like 60 to 65 degrees, that might be tuff to do. However with winter here, you might be able to do it in an unfinished basement. Plus you could put your reservoir on the concrete floor and it would cool the water down.
I may try this at some point to see if it would work.