Depending on the bulb, there is often little difference between T8 and T12 bulbs both in lumens (what humans see) and PUR (more important, what plants want). If in your situation I would buy daylight/aquarium or full spectrum T12's.

It might be a defective fixture. some T12 light fixtures will use T12/T8, others only T12. You can still buy the T12 for now, I've heard that they will be discontinued in near future. All my lights are now T8. When I buy them, I mark whether the box states T12 or T12/8 or T8, making it easier to know whether the different bulb will work.

I've noticed that alot of store are discounting the T12 only fixtures lately.

go onto ebay and get used t8 fluorescent ballast. Read about how to overdrive fluorescent fixtures, and turn your cheap shoplight into a lighting powerhouse, for very little money. a used appropriate ballast is about $10 - buy the ballast that is designed for 4 lamps, instant start, and use two leads for one lamp and 2 leads for the other lamp- your 32w t8 will be running at about 50watts and will put out the increased amount of light that will make your plants really happy - paul m. (that's what i do - anyway)

I ended up taking the fixtures back to Home Depot and instead settled on the Walmart ones that said T-8 on the box. I'd rather stay in the T8 world, but changing ballasts sounds interesting, so I should look into that for next year. I don't really need to accelerate growth and development though that would be a good catch-up if I get too lazy seeding for my late April\early May batches of tomato plants I sell locally.

I use CFL's in closed boxes 4 ft by 4 ft with the Heights to plant needs. They work better than my tube lights by a long shot. Because the ballast is with the bulb there is no trouble shooting, just change the CFL and away you go.
SEE PICTURES

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This is where my starts are placed after ,growing in my CFL powered bucket and box light systems
CLICK ON THE LINK BELOW

Here is a link that might be useful: https://plus.google.com/photos/111099372377958308731/albums/5864651368775846321?banner=pwa&authkey=CI763rvAj8eLAg

That's fantastic poncirusguy!

Thanks for sharing! Simple and very effective!

Here's my current setup. I use an old server console rack with shop lights hung on the shelves. I used a giant sheet of reflective Mylar on the backside to keep the light inside the giant 'box'

Hi bencjedi
You have quite a setup yourself. storage containers with tomatoes popping through holes in the lids. I saw what looked like cat litter buckets with pepper plants. I have 5 gallon buckets with peppers and eggplants. I am trying some thing different this year. Lots of frost covers and cold frames. You appear to have completed what I am in the early stages of. Thanks for the pics.

My sites are public so feel free to look beyond the direct links
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Skyscraper eggplant starts
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Skyscraper pepper plants from over seas 200 years back
{{gwi:1142}}eppers on the rail.
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Pear, 2 apples, 2 sweet cherries, 3 grapes, 2 gooseberry, 3 rhubarb, 3 kiwis, 3 sweet lee tangerine seedlings
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Spinach field with brussel sprout front left
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Broccoli 16 plants
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2 pear trees maxine to left, moon glow to right
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the climb down out of the garden

Click on the link below to see more

Here is a link that might be useful: https://plus.google.com/photos/111099372377958308731/albums/5864651368775846321?banner=pwa&authkey=CI763rvAj8eLAg