Lifespan of T5s?

[cpreefguy]

What do you mean by being overdriven?

That is when you put them on a bigger ballast, driving them over their listed wattage.
You can overdrive them at different rates, but it is not really a cost efficient way to get more light output. You will be replacing your bulbs so often that the cost will catch up with you, fast.
Depending on how much you overdrive them, it can decrease their life to as little as 3 months.

[d3rryc]

You can hook up a T5 bulb to a ballast that is more powerful than the one the T5 was designed for. You get greater output from the bulb, but at the expense of shortening its life.

[alton]

For a little clarification in the 46" T5 line there is T5 28 watts, T5HO 54 watts, and T5VHO 80 watts.