i personally have 3 plants (small op) growing under a 6tube 4ft T5HO setup, and so far couldnt be happier. gave my 3 girls 18/6 for 25 days from seed, was able to get 6 nodes while still under 6" tall (had to pull the light away a bit farther at start of 12/12 to get a bit of stretch goin). only reason i went with this option was due to heat, as we dont have AC and it gets quite warm in our house during the summer. less than 350 watts, over 25,000 lumens, and incredibly low heat output. since i don't know the specs of your chamber, i don't know if a tube ballast like this would work well for you. but they do have 2,4, and 6 tube 2ft setups as well, for smaller spaces. then of course, you could always go with the classic 150, 200, or even 250W+ (true watt not equivalent) for a large amount of lumens vs a low amount of heat. the biggest problem with these is penetration, but if you can manage to get a couple, and spread them around the canopy a bit, they should still work quite well.
if you do not have to worry about heat i would still just get an HID, preferably MH for a veg room. you will get the most lumens/watt.
