Teach me about Fluorescent Ballasts

[corrado33]

Hey guys. I'm building a canopy for my little 12 gallon today, and it got me thinking about eventually buying some fluorescent lighting to put in there. Right now I'm just going to cannibalize two aquarium lights and make them fit. Anyway, I want to learn about ballasts. From what I can see, they generally drive bulbs that have part numbers like this... F40T12. Anyway, the "T12" part is obvious, that's the type of bulb. For a T5, it's be T5 at the end. I think the F stands for fluorescent, but what's the 40? These bulbs are 4 feet long, but I don't think the 4 feet has anything to do with the "4" in "40".

In case you were wondering, I happen to have a couple of these ballasts, as we have fluorescent lighting in our garage and basement, and we had extra lights.

My main question is, why do ballasts have to drive certain bulbs? What makes a 4 foot bulb different from a 2 foot one? I'm assuming it'd have to do with the power needed to drive it, but what if you found a 2 foot bulb that took as much power to drive as a 4 foot bulb? Could you use the same ballast? (Assuming it needed the same amperage and was the same wattage) Still, I mean I wouldn't think that fluorescent lighting needed such specific power requirements, the chemistry geek in me knows how they work on a quantum level, and I'd guess that a little more power would simply change the spectrum of light that came out of the bulb. I don't know, that's why I'm asking!

TIA

 

[BigJim]

Ballasts don't have to drive any specific bulb. They're recommended to drive bulbs that will use most to all of the power put out by the ballast. Undersized ballasts won't fire a bulb properly and oversized ballasts will overdrive the bulbs, causing them to put out more light, but they burn out faster as well. I'm sure there are other factors, but that's the simplified version as I understand it.

 

[BillD]

The 40 is watts, T12 is the size in tenths of inches, and ballasts are designed to drive certain tubes. It may be more than one exact type, but they do have design criteria. Right know, T8 is the economical sweetspot, with a good variety of tubes available for little money. Electronic ballasts are preferable to magnetic and are more energy efficient. For small tanks, you can use compact florescents in place of incandescent bulbs. Again, you can find a variety of colour temperatures, with 5000K and 6500K being readily available, both of which will give pleasing light and grow plants.

 

[thincat]

T-12 = 12/8=1 1/2" bulb. It's not in 10ths of an inch....