we don't know that. Pictures would be helpful here, NJ Bob.
T5's are better, but I have grown plenty of seedlings with T8's, without stretching or bleaching (etiolating). You just have to be sure the lights are right down close, just 1-2 " above the seedlings and on 16 hrs a day.
And we don't at all know that high intensity lighting like metal halide or sodium vapor lamps are appropriate for him. They draw intense amounts of power and will up your utility bill like crazy and they give off a LOT of heat, especially the hps, so then you have to have lots of fans/ vents or whatever to deal with the heat. And to have 12 feet of lighting, they are way more expensive than fluorescent tubes.
I grow about 500 or so plants a year from seed with my 16 feet of fluorescent tubes.
But yes being organized about it and knowing what to start when helps. I have been doing this about 20 years now, so I have it all down. I start the cold weather stuff, cabbage and broccoli, etc., very early. So then by the time the warmer weather stuff needs to be spread out (I start the seeds very crowded initially, because I only run two heat mats) and starts taking up a lot of room, the cold weather stuff is already out hardening off.