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Question 1152

I was told by an electrician to use 130-volt bulbs, which he said were outlawed by the electric bulb makers because they last so long. He said that electricians can buy them and not the public. I found them and have used them for 5 years and he is right! They last forever. Why is that? How do they compare to more energy efficient lights? — J
When you use a bulb designed for 130 volts in a fixture that operates at 120 volts, the bulb's filament runs at less than its rated temperature. This temperature change has two consequences—one good and one bad. The good news is that operating the filament at less than its normal temperature slows the evaporation of tungsten atoms and prolongs the filament's life. That's why your bulbs are lasting so long. The bad news is that incandescent bulbs become much less energy efficient as you lower their filament temperatures. The light emitted by the filament is thermal radiation and its color spectrum and brightness depend almost exclusively on its temperature. These 130-volt bulbs emit redder and dimmer light than a normal bulb and they are significantly less energy efficient as a result. Incandescent bulbs already emit far more invisible infrared light than visible light and operating them at reduced temperatures only makes this problem worse. I recently read the statement "this bulb burns cooler than a normal bulb" on a package of super-long-life bulbs—as though burning cooler was a good thing rather than a serious shortcoming.

As energy becomes more and more precious, making the most of it becomes more and more important. I would suggest saving these 130-volt bulbs for fixtures that are so difficult to reach that you want to avoid changing bulbs at all costs. In more easily accessible fixtures, replacing bulbs is only a minor inconvenience associated with improved energy efficiency. Better still, switch to fluorescent lamps—which are much more energy efficient than even the best incandescent lamps.


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