What is the difference between T5, T8 & T12 lights?
 

I was putting up another light source in my basement greenhouse and discovered that my T12 bulbs don't fit. The light is mounted in the ceiling and now I'm wondering if the T5 will work for reaching the floor. This particular light isn't necessarily for orchids, more for my other tropicals. But since I don't understand the difference in the bulbs, I am wondering if I am even using the right light for my orchids, lol...

Any info that can help me to distinguish the difference between them would be greatly appreciated.

Thanks in advance.

The main difference has to do with the diameter of the tube and as a result a T5 holder and a T12 are different. Due to the way that the lights work a T5 can produce more light.

Interesting you brought up the question--I was just trying to figure out the same thing and doing some research. I found the following two links helpful T5 Fluorescent Grow Light Systems for Plants from ACF Greenhouses and T5 HO Fluorescent Lighting Technology I won't necessarily order from these companies, but I found they had useful information.

Basically, the number following the "T" is the nominal tube diameter expressed in twelfths of an inch - T5=5/12 (~1/2"), T8=8/12 (~3/4"), T12=12/12 (1")

NEB is right - you get more illumination from the smaller tubes.

WOW, I was going to return the T5 holder because I thought it would produce less light. This is great info! Thanks guys!