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What's the physical reason that makes compact fluorescent lamps (CFLs) burn out earlier if we frequently switch them on and off?

CFLs typically have a rated service life of 6,000–15,000 hours, whereas standard incandescent lamps have a service life of 750 or 1,000 hours.[16][17][18]...

The life of a CFL is significantly shorter if it is turned on and off frequently. In the case of a 5-minute on/off cycle the lifespan of some CFLs may be reduced to that of incandescent light bulbs.

In incandescent bulbs, the heating-cooling causes thermal shock in the material making it break eventually. But in fluorescent lamps the gas glows and it can't wear out in the same way the regular filament does. Also the glow only sputters the electrodes when the lamp is on, so this also doesn't explain why switching have negative effects.

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A Fluorescent lamp ballast provides a spike of high voltage that starts electrons flowing from one electrode to the other. After ignition, once an arc of electrons is flowing through the gas, the voltage requirement drops significantly as current begins to pick up on its own. The function of the ballast is to regulate voltage from high at startup to low during operation. If there were no ballast, the self-increasing current would burn out the tube in short order.

Instant-start and rapid-start fluorescent lamps require about 1.85 to 1.70 times more voltage to start the lamp than is required to keep it glowing. The ratio of starting to average voltage is called the "crest factor". A high crest factor causes great wear on the electrodes of the lamp.

This is why: Electrodes generally are made of tungsten and are coated with an emission mix that generates electrons that arc from electrode to electrode inside the tube. High voltage at startup really pummels the emission mix. As the tungsten electrodes lose their coating, the fluorescent light may darken near the electrodes. When the electrodes no longer emit sufficient electrons, the light burns out.

As startup rapidly depletes the coating on the electrodes due to the high voltage required to get an arc going, frequent startups will shorten the life of the bulb.

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Apparently, that's a myth. If I had to guess, I'd say it comes from people assuming it's the same for all types of bulbs. (That, or poor quality of the bulb)

See: https://sustainability.stackexchange.com/questions/54/what-s-the-best-strategy-for-turning-off-cfls-that-will-save-energy-but-not-redu for more details

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  • $\begingroup$ I added a quote from wiki to the question. Is wiki totally wrong on this? $\endgroup$
    – innisfree
    Jun 5, 2015 at 14:28
  • $\begingroup$ I saw the wiki quote when I searched info on this, I also saw a few more sites. None of them included their source, and this one did. And this one actually makes sense, unlike those. $\endgroup$
    – Omry
    Jun 5, 2015 at 14:31
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    $\begingroup$ It's not a myth, there is actually serious government sponsored research about that because energy savings in office buildings requires to turn fluorescent lights on and off frequently, which does limit their lifetime if they are being started with a conventional (passive) ballasts. There are modern electronic ballasts that mitigate the problem, however, there is no guarantee that the Chinese manufacturers of most CFLs in service care about that and even Western manufacturers are not disclosing lifetime data properly (there are good business reasons for that). $\endgroup$
    – CuriousOne
    Jun 5, 2015 at 15:14

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