Archive for January 2nd, 2009

Fluorescent Shop Lights, Early Failures Thereof

A decade ago I installed a few dozen two-tube fluorescent fixtures (a.k.a. “shop lights”) throughout the basement. Visitors always say something like “Wow, I can actually see what I’m doing!” That was the whole point, of course.

Being that sort of bear, I write the date on one end of a fluorescent tube when I replace it. Tubes seem to last 3-5 years, which is short compared to the 20k power-on hours touted on the carton: 5 years * 300 days/yr * 6 hr/day = 9 k hours. That’s an overestimate, as I don’t spend all my time crouched in my basement laboratory, honest.

It turns out that there’s also a spec for the number of lamp turn-ons (“starts”) hidden deep in the lamp datasheets. For example, if you manage to browse the current Lamp and Ballast catalog at, you’ll find that a 20k hour rated life comes at “3 hr/start”, which works out to a mere 6.7k starts over the expected life.

More starts = shorter life.

I tend to turn the lights off if I think I’ll be upstairs for a few hours, which happens a lot during the winter.  My back of the envelope says that the tubes fail right around the expected value: 5 years * 300 days/yr * 4 starts/day = 6 k starts.

Lately I’ve had a rash of early lamp failures and it seems the fixtures are failing after a decade; nothing lasts any more. I’m now installing electronic-ballast fixtures that fire right up in the winter and don’t have that annoying subliminal flicker. At a cost of $20 each, I’m not replacing all of them at once, I assure you.

The only real problem with fluorescent lamps is that they make white people look dead. I managed to buy a contractor pack of warm-white tubes at the local Lowe’s, but they’re hard to find around here. Go for the lowest color temperature bulbs you can find.

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