Quality fluorescent tubes should last at least 20,000 hours as a plant light, that's five years.

Diane,

Even my $2 cool white Philips T8 fluorescent tubes are rated at 20,000 hours. What kind of bulbs are you using?

Are you sure it is the bulb that is burning out, and not an electronic fluorescent ballast? My electronic fluorescent ballasts are susceptible to line current fluctuations, and I protect them with inexpensive surge protectors.

Even the switching of an electric timer switch can cause surges that can potentially damage some electronic ballasts. If you don't have a surge protector in your lighting setup, I advise that you get one.

MM

Make sure the little notches on the metal at each end of the bulbs are aligned with the centers of the fixture openings. If they're not, the bulbs can burn out quickly. A warning sign is if you can see gas swirling around inside the bulb or the ends are turning dark.

Bulbs tend to grow dimmer over time, so they should be replaced much sooner than their rated life, or after about a year of use as grow lights.

Bulbs tend to grow dimmer over time

Quality modern fluorescent tubes hardly change in brightness right up until they fail, about 5% down is what you should expect, it will usually tell you on the label. No need to swap them out like your grandfather used to :)

El Cheapo fluorescents do still decrease in brightness, it can be 20% or more which is hardly noticeable by eye but significant to plants, these are less and less common with changes to regulations on energy efficiency. Those expensive grow lights with their unusual spectrums also decrease significantly in brightness and should be swapped out every couple of thousand hours.

And the big gotcha, those cute little compact fluorescent spirals which are so handy for lighting a couple of plants or starting a few seeds show horrible loss of brightness after as little as a thousand hours. You can easily spot the difference between an old one and a brand new one. This is one of the reasons that they no longer claim a 20W CFL is equivalent to 100W incandescent, its equivalent for the first few weeks out of the box, then you're sitting in the dark ;)

Good to know! Here I was ready to invest in those CFLs. How about T5 bulbs? What do they do over time, and how do you tell if you have quality or el cheapo (well, el cheapo is easy to tell, but quality isn't!)

All T5 tubes have essentially the same spec and the same spectrum, they are all modern triphosphor tubes with very good lumen maintenance and long life. T5 ballasts are similarly all high frequency electronic ballasts giving good tube performance. Just a shame that they are so hard to find in the US except from very expensive specialist stores.

Don't let me stop you using the compact fluorescents, they are ideal for lighting small spaces intensely, just as efficient as two foot straight tubes and much more convenient. It just makes sense to know what they will do. I move them from the propagator to the porch when they start to get dim ;)