I've tried both and much prefer the T5's. I stress prefer purposely because I was able to start seedlings with the T8's. But, no surprise to some, I think the T5's are more effective. Think extra light in the same space for less power. No leggy seedlings, no need to keep the fixture directly on top of of the plants. More air movement due to more space under the lights. Less stress on the plants - think better light penetration to the lower leaves of taller plants - no phototropism due to insufficient light. One warning - the t5's get hot. You in fact can't keep the light right on top of the plants. Do so and you will cook yer babies. Now, I started seedlings for years with a dual T8 fixture. The seedlings were usually leggy - despite having the light low and a fan on the side blowing over the flat. Unless I got them outside under stronger light after the second or third sets of leaves, they were inevitably tall and thin. I live in the Chicago suburbs. Getting them out early is not usually an option. So, it made sense for me to get the stronger lights. Pricey, but I'm happy with them.

I do it because I get unusual plants/exotic colors only catalog seeds can give me. I do it because I like doing it. Yes, you can get earlier bloom with some plants. With others (like cosmos and zinnia) I find they do best planted directly outside. You learn from experience. Lately (after doing it for 30 years) it's become a bit of a chore so I stopped doing seeds that need to be started before March 1st and buy those plants in the nursery. I use an 8 tray light setup with two shop lights next to each other on each level, each light with one ordinary 40 watt tube and one full spectrum tube. Keep a list of when each plant needs to be started (by weeks before last frost), keep the lights no more than an inch from the plants, and always have a fan or slightly open window in the plant room to prevent fungus. Try to water from the bottom and without soaking the top of the soil. Have as much fun with this and go nuts obsessing over whatever you feel comfortable with. Rewmember, it's for pleasure!

You should wait to turn on the overhead lights until they break the surface. As an aside, you are going to have to remove the dome when the coles and tomatoes come up, even if the peppers are not up. The peppers will probably take a week or so longer than the others. The coles will probably be up in 3-4 days, tomatoes 4-7 days and the peppers (even with the heating mat) could take up to 3 weeks, depending on your variety. Try to keep the lights (if they are CFLs) as close as possible to the plants and on for about 16 hours/day. 2-3 inches from the tallest leaf is standard. You may need to adjust things from tallest to shortest and raise on side of the lights higher than the other as they grow.

I took over an upstairs bedroom to start seeds indoors. I bought a couple mini-greenhouse assemblies and hang lights from short chains. I can fit 15 trays under the lights. I used 4' shop lights with cool bulbs. I have read that it might be better to use one cool and one warm but I've found the seedlings do just fine with what I have. I leave the lights on 24 x 7. The lights should be about 2" above the seedlings in the tray. For the most part I use the basic cellpack trays that hold 8 6-packs. Keep the lids on the trays until the seedlings sprout. I started using a potting soil from my local hardware store. But then I found smaller bags from Ocean State Big Lots for much less money and the seedlings did just as well. I hadn't even paid attention to if it had fertilizer included in the mix. I did use a liquid root stimulater root fertilizer on the perennials I started. I also did some repotting of mainly perennials into yogurt cups and 3" pots this year. I started perennial seeds in Feb and Mar and planted them out in early May for the most part. I moved one of my greenhouses outside for the hardening off process while other seeds were still inside under the lights. The green seedling trays in this picture were $1 from Christmas Tree Shops and worked great when I only wanted a small amount of a particular plant. I started the seeds over a couple different timeframes. I started the perennials first and got them off to a good start and then started a lot of annuals in early-April. I did a lot of wintersowing this winter as well. I have the space to start indoors and I found the seedlings were much larger than those I WS'd and many are blooming already. It does take much more work though (and $$ for electricity).