BOTH - The T5 is more than just being more efficient - you can get 44 watt HO T5 that put out 5000 lumens each and use growlights bulbs that are at 6500K for best seedling development they come in 2 bulb 8 bulb or 4 bulb units - and 4' is best length but they do have other lengths
Dennis

should be 54 watt

So if I'm getting 16,000 lumens with the current 6 T8 over driven bulbs, I would want a T5 setup that puts out 16,000 lumens as well?

A 4'T5 HO unit will produce 5,000 lumen per bulb so a 4' 4 bulb HO unit with 216W should produce 20,000 lumen. If you are successfully growing with the current lighting then the T5s should do even better.

OK, so I got another question.

Is it possible to build your own light fixture out of wood, or is it necessary to buy the rip off $150 4 bulb fixtures so the ballast grounds correctly?

I bought ballasts, endcaps, bulbs, and reflectors, and mounted them on a plywood sheet cut to size. I used a three prong power cord and attached the ground wire to one of the ballast mounting holes. Then I screwed in some hooks and hung it with with some small chain. It works great.

penfold2 How much did the supplies cost? Excluding the wood of course. I can get that free.

And what ballast did you get?

I made two 4-bulb fixtures. Here are the parts I used.

2 Universal Accustart B454PUNV-E ballasts: $27 each + $10 shipping on ebay

Endcaps: $2/pair

2 6-pack TCP 54w 6500K bulbs from businesslights.com: $47 + $19 shipping (leaves me with 4 spare bulbs)

8 IceCap SLR clip-on reflectors: $25 each

2 grounded power cords: $3 each, or free if you can cut one off of something

That's about $350, or $175 for each 4 bulb setup. Over half of that cost, though, is the reflectors. I splurged on some aquarium ones that focus the light in a very tight downward pattern. If you can find some cheap reflectors, you could save a lot. A local source for bulbs would save on shipping as well.

Penfold:

How did you ground the ballast? From the spec sheet of the GE T5 ballast I'm going to probably get it says there's a green ground wire which needs to be attached to the metal fixture.

The ballast can be grounded simply by attaching the ground wire on the power cord to the ballast's ground wire or the ballast case itself. The reason the GE ballast says to connect the ground wire to the fixture is because with a metal fixture, this would ground the reflectors as well. Some ballasts can have trouble starting if the reflectors are not grounded, but I don't know how common this is. I did not ground my reflectors and I've had no problems. The correct way to do it with a wood fixture would be to attach an extra wire to all of your reflectors and run that to the grounds on your ballast and power cord. This would ground both the ballast and reflectors.

I'd just ground the ballast since it's simpler and worked fine for me. If the bulbs won't light, then you can consider grounding the reflectors as well.