During some HAST testing of incandescent bulbs in the 90′s found that life varied inversely to the fifth power with increasing voltage. Line drop gave long life to incandescent bulbs. Haven’t seen any HAST results for CFL or LED bulbs.

a life of 12,000 hours

Which is 500 days at 100% duty cycle, minus damage from vibration & power glitches. Looks like a year or two, at most.

Of course, the box will claim that to be 8 years at 4 hours/day, which I think we all agree is bogus.

quite a production to drag out the ladders and safety equipment

They can’t just stand on a chair like I do, that’s for sure. I’m sure there’s a scissors lift platform involved!

The ones I have on hand claim a life of 12,000 hours which is more than 10 times the expected life of an incandescent but much less than five years. They don’t last that long for me (5/2011 to 3/2012 for the last one for my porch which is on all the time.) so use one year as a ballpark figure.

I suspect that it is quite a production to drag out the ladders and safety equipment to replace those lights. I suspect that doing that once a year instead of once a month or so is considered a big win.

First, the older ones tend to last a long time.

Which suggests they predated the cheapnification that allows current models to sell for next to nothing… and fail next to instantly. Verily, they don’t make ‘em like they used to!

Heat is an issue.

I have several can lights in the Basement Laboratory Office Wing ceiling and specifically got CFL bulbs rated for “burn base up” duty (more specifically, ones that didn’t prohibit BBU installation). Most died over the course of a few years. That’s tough service, but … c’mon, that’s how ceiling lights work.

Maybe the new LED bulbs will be better; I’m hoping so, anyway.

Heat is an issue. I have a couple of dual-bulb fixtures on the same switch as single-bulb (er, the twins use 25W, while the singles are 13) and the twins to tend to crap out faster.

Vibration is murder on a CFL. I tried one for illuminating workpieces on a mill-drill, and it lasted an hour. When I was reroofing the house a few years ago, I had to replace a fair number of ceiling bulbs during the project. Those in hanging fixtures or floor/table lamps installed at the same time, no problem. In general, the closer the bulb was to my banging around, the more likely it was to fail. (We’re in a well-insulated triple wide manufactured home. The problematic areas were where we were about a foot between the ceiling and the roof.)

Back when our power quality was fairly bad (lots of glitches and outages) we lost bulbs quickly. Mostly, the appliance and other electronics did OK (barring the late bread maker), but CFLs weren’t happy. Fortunately, we got another substation online and the power was improved. Ah, life in the country!

a vast increase in failures in year x

Without knowing anything else, I’d expect the usual bathtub failure curve: plenty of infant mortality tapering off to nearly nothing for at least a few years, then a steep rise as the remainder fail. But I have absolutely no data to support that expectation!

no discernible pattern in failures

The same thing happens here: some fail almost immediately, others last basically forever. On the whole, however, there are more failing much sooner than they should.

I’ve definitely pulled far more than a few percent per year of deaders around here…