heat might not be a problem... but i would think that if the leaves were in direct contact with the bulb, it might be too bright for them.

depends if you are growing high light plants or not. There are 3 types of light collecting cells...

I measured my T-8's with my infrared pyrometer. The temp was 100F/38C. This is not too hot for leaves in my experience. But I am talking high light plants...I don't know about orchids up close to t-8s(phales in particular)

My overdriven fluorescent is 120F/48C and this *is* too hot for them. Cut off in my experience is 112F/43.5C.

Another way to tell is that if the leaf is hot to the touch, it is not transferring the heat efficiently and cell death or leaf scorch can start to happen.

Bright light without heat probably won't harm your plants. Combine light and heat and you've got a disaster.

Place a fan in between the plants and the bulbs and you'll probably be allright.

Sam

sam- actually, i think it is possible to give a plant too much light. i posted this question on the AOS forum a while back and the general consensus was that too much light (that is, too bright light) can be harmful. i have witness this with some of my lower light plants. some of the plants' leaves turned very red, and some began to wilt. i noticed this particularly among phals, but also in other plants. i have not tried to see if it's possible to sunburn the plants solely through light intensity (not heat), but according to some it can happen.

And it may be possible. However I think it would be very hard to do if you've removed the heat component. The reddening isn't a bad thing, either. It's just the activation of the anthocyanins in the plant cells.

San

i know, red leaves are usually considered as a "good" sign, but some of these were turning extremely red and then starting to wilt.

I've got a phal that's turning extremely red but not wilting, or burning. I'm pretty sure it's because of very sufficient light as well as the fact that it's a Dtps cross. My Dendrobium is spiking and is turning purple in areas, too.

I used to have the opposite problem-wilty, weak orchids.

Sam

OK..thanks for all the good advice...Ive been letting my Citrus leaves (various types) touch the bulbs for close to a week now, and haven't noticed anything....I'll let you know if anything does arise... I would think if any plant could take it, a citrus would...Citrus grow well in Desert areas if i'm thinking right...my little avocado is laying his new leaves on the light! oh well...he's growing like hes taking steroids...

thanks again

another thing...the room my plants are in is generally cool, and the light is closer to the floor then the ceiling, therefore the heat should be able to dissapate(?) well...in a warm room, i could see problems from heat, although T8's are very cool(compared to every other light ive used, even 15watt CFL's)...

Plant leaves can burn even when touching lighted T12 tubes. It's a function not only of heat but of leaf type (thickness, presence of waxy coating etc.). Citrus leaves would likely be more resistant to burning than, say coleus leaves.