Archive for September 6th, 2012

Compact Fluorescent Bulb Lifetime: Another Data Point

Each of the three chandeliers in the Poughkeepsie Train Station sports 36 bulbs in two rings. When the station opened in 1918 they installed those newfangled incandescent bulbs that were all the rage at the time. The color of the bulbs in this Wikipedia picture, dated October 2007, suggests that tungsten ruled for at least nine decades:

Poughkeepsie Train Station Interior

Poughkeepsie Train Station Interior

Since then, they installed chunky compact fluorescent bulbs that probably provide the same amount of light, minus the pinpoint highlights from tungsten filaments in clear bulbs. This view from below the central chandelier shows the layout and some detail of the carving & decorative sockets:

Pok RR Station Middle Chandelier - detail

Pok RR Station Middle Chandelier – detail

In addition to being decorative, those chandeliers also give useful data on the reliability of compact fluorescent bulbs. With the contrast stretched the other way to make the bulbs easier on the eye, count the number of deaders in …

Chandelier 1:

Pok RR Station Chandelier 1

Pok RR Station Chandelier 1

Chandelier 2:

Pok RR Station Chandelier 2

Pok RR Station Chandelier 2

Chandelier 3:

Pok RR Station Chandelier 3

Pok RR Station Chandelier 3

I took each picture from a vantage point showing all the deaders; the bulbs hidden behind the central dingus work.

Let us assume all 108 bulbs were installed at the same time and, given the number of deaders, haven’t been touched since then (although they’re not covered in fuzz, which suggests that they’ve been dusted within living memory). I was there in mid-afternoon, so the bulbs probably burn 24 hours/day and aren’t subject to early failure from frequent starts.

So, in no more than five years, 108 CFL bulbs have a 4.6% failure rate, which works out to 0.9%/year, more or less, ignoring any infant mortality. If they’ve been up there for the last 2.5 years, then it’s 1.8%/year.  Replacing deaders since installation, of course, makes it worse than that.

Over the course of a decade, a compounded 0.9% failure rate will kill 9.4% of the bulbs. After 20 years, 20% will be dead. A 1.8% annual failure rate kills 20% and 43%, respectively.

Now, I’ll grant you that tungsten bulbs burn far more energy over that time, but replacing a percent or two of those complex and somewhat eco-hostile CFL bulbs every year cuts away a big chunk of the rainbows-and-pink-unicorns delight involved in Saving The Planet.

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