I have a large seedling cart with dual T5s on each shelf. I keep the lights 4" from seedlings and they still dry out pretty quickly. I have to check them everyday to make sure they are not completely drying out. Using a fan can help with the heat but it also makes the seedlings dry out faster.

T5's burn hotter than T12s, especially at the ends.

I have that same fixture and another Sunblaze 4foot x 6 lamp. I keep the lights 8 to 10 inches above the seedlings and have to water them every two days. No leggy seedlings so far.

Thank you for your replies and also sharing your pictures. I am sure now that 2 inches is way too close for this light. I moved them down about 5 more inches and as of tonight they are doing much better already. I am also working on a fan too. I think they need it. I work from home, and they are in my office, so I can keep a very close eye on them. Thanks again for sharing.

I have seedlings and transplants in three inch pots under T5HO's. Two inches is fine for the transplants. The seedlings under the same lights in seedling trays are more like 4-6 inches, and they seem fine. Smaller plants can only use so much light.

Constant watering is not always a bad thing as long as it's done before things get too dry. It's better then pots staying wet too long. Having to water means that roots are getting air, which helps a lot. It's an inconvenience to the grower, but plants love it. I guess if they get too dry before you come home from work, then it's an issue. One possible solution is to use a tall clear dome with vents. Just be careful not to let plants stay too wet using a dome.

These seedlings are too young and thus transpire water faster than the roots can drink. Pull up that light to about 12 inches above plants, then in ine week, start loweing it one inch every 2 days to about 3-4 inches from the plants. Thatll give them time to establish themselves better. Remember that the closer you can keep that light to the plants, the more PAR light is available, which is what you want.

I just started using a four-foot eight bulb t5HO fixture three weeks ago to start my seeds after many years of using shoplights with t12 bulbs. I kept the t12s as close as possible to the plants, often one inch. I quickly found the t5s are much hotter as well as brighter. At two inches, the potting mix was close to 90F. Most of my seeds sprouted within a few days, so I raised the lights. I have the lights 5-6 inches from the tops now. I am amazed by how stocky the little plants are now. I had a few clivia seedlings at one end of the garden that actually became sun bleached in a few days with the lights six inches above them. Clivias are not sun lovers like most vegetables.

Big difference with an 8 bulb there Ohiofem, although 2 bulb is usually enough for seedlings. 8 bulb is not far from 400W HID equivalent, more suited to mature plants. Even a two bulb T5HO is around twice as many lumens as the equivalent T12.

I usually start about 6" from the seedlings with two T5H0's, and allow them to grow toward the light, then raise them as they get to about 2".

10-12 inches from the tops of seedlings. Then, when the plants become about 4-in tall, reduce to 6-8 inches from the tops. Finally, keep within 4" from the tops for mature growth. You can flower/fruit these plants under that light. Probably only one or two or three containers worth, given the strength of the light... but still... it's possible.