4 ms·

This is an interesting bit: > While it might seem astonishing that so many longest-lasting light bulbs have been so infrequently turned off, this is the precis

This is an interesting bit: > While it might seem astonishing that so many longest-lasting light bulbs have been so infrequently turned off, this is the precise reason for their longevity. Most of the wear and tear that leads to burnouts in incandescent light bulbs is caused by turning them on and off, not by burning them. Each time the bulb is turned on and off, the filament is heated and cooled. This causes the material of the filament to expand and contract, in turn causing micro stress cracks to develop. The more the light is turned on and off, the larger these cracks grow, until eventually the filament breaks at some point, in non-spectacular fashion, thus causing the light to burn out. I knew running filament bulbs on low voltage is the key to their longevity, but this is another important aspect

memefrog 3y ago
That's really not written in Wikipedia's tone.
0xEF 3y ago
This idea is in direct cobtradiction to the claims that the Phoebus Cartel gathered to lower the lifespan of light bulbs due to declining sales in a market saturated with long-lasting bulbs. This is cited by some as the birth of Planned Obsolescence. I personally have not be clear on which side of this argument holds more accuracy, but given today's anti-consumer leanings in manufactiring (particulatly in the US), I have my misgivings about it all. https://en.m.wikipedia.org/wiki/Phoebus_cartel https://en.m.wikipedia.org/wiki/Phoebus_cartel
- eru 3y ago
  Compare https://news.ycombinator.com/item?id=37046713 https://news.ycombinator.com/item?id=37046713
magicalhippo 3y ago
I noticed this early on when I noticed how often I changed the light bulb in the bathroom compared to the hallway where it was always on. Once I thought about it, I assumed it was due to thermal stress.
- ekaryotic 3y ago
  I'm sure it would be possible to extend bulb life by ramping up the voltage slowly to reduce the thermal stress. not worth it in most environments, but in a bathroom, why not. I understand there are soft start mechanisms used in certain electric motors, i know of an anglegrinder that used one. maybe i could do a transplant some day.
  - rocqua 3y ago
    I recently retro-fitted my portable table-saw with a soft-start. The process is quite easy, though the soft-starter you use has to be picked for a certain power-draw. And they might be specific to the type of load (i.e. specific to a universal AC motor) I got my soft-starter from amazon for €10.
  - deepspace 3y ago
    A few years ago, I retrofitted my entire house with Lutron Caseta switches, for home automation purposes. The Casetas allow me to soft-start each bulb, and to run lights at less than full brightness most of the time. It would have been interesting to see the effect on incandescent bulb life, but I also took the opportunity to replace all light bulbs with dimmable LCD, so the question is moot.
- Ekaros 3y ago
  What type of bulbs are we talking about? I could see leds and CFL being affected by moisture in bathroom. Also bathroom could be slightly hotter and worse ventilated than hallway.
  - magicalhippo 3y ago
    This was incandescent bulbs. For LEDs the issue is the driver boards, they get crammed into the tiny socket and live a very, very hot life. Doesn't matter that the LED has 100000 hour lifespan or whatever they write on the box when the driver dies after 5000 hours.
pfdietz 3y ago
I don't believe that theory. Instead, I think incandescent bulb lifespan is limited by sublimation of tungsten.
- Timon3 3y ago
  Do you have a basis for not believing it aside from you having a different theory?
  - pfdietz 3y ago
    You will note that incandescent bulbs gradually get dimmer as they age, due to deposition of tungsten on the glass. Also: http://donklipstein.com/bulb1.html http://donklipstein.com/bulb1.html "Due to the high temperature that a tungsten filament is operated at, some of the tungsten evaporates during use. Furthermore, since no light bulb is perfect, the filament does not evaporate evenly. Some spots will suffer greater evaporation and become thinner than the rest of the filament. These thin spots cause problems. Their electrical resistance is greater than that of average parts of the filament. Since the current is equal in all parts of the filament, more heat is generated where the filament is thinner. The thin parts also have less surface area to radiate heat away with. This "double whammy" causes the thin spots to have a higher temperature. Now that the thin spots are hotter, they evaporate more quickly. It becomes apparent that as soon as a part of the filament becomes significantly thinner than the rest of it, this situation compounds itself at increasing speed until a thin part of the filament either melts or becomes weak and breaks." Halogen bulbs last longer because the sublimated tungsten is converted to volatile halides, which then preferentially decompose back to elemental tungsten at the hot spots, healing them.
- rcxdude 3y ago
  Both are relevant, and can feed into each other. A incandescent lightbulb that has been on for a long time is more likely to fail after a power cycle, as the cycling adds additional stress (anyone who's used them can attest to this: the most common experience with one failing is going to turn it on, only to get a brief flash of light before it fails).
mechhacker 3y ago
This is true for a lot of mechanical devices. For example, turning engines on and off heavily thermally cycles them. It can get worse when they are rapidly cooled or rapidly heated. Jet engines running at constant speed have high cycle fatigue to worry about, but steady temperatures don't pose a thermal stress issue. But shutting the engine off in cold air and letting them go from very hot to very cold suddenly will cause the thicker parts to cool slower than the thin parts, stressing them near the change in thickness. That results in low cycle fatigue (where you can count the cycles to failure in the dozens/hundreds/thousands vs. millions/billions for high cycle fatigue).
Workaccount2 3y ago
I had some recessed lights in my ceiling that I installed in 2000. They worked daily for 20 years before I swapped them out for LED lights. Never had one fail. I attribute it to the fact that the dimmer switch they were on could only do soft turn ons and turn offs. Always took about 3 seconds to turn on and off.

memefrog 3y ago

That's really not written in Wikipedia's tone.

0xEF 3y ago

This idea is in direct cobtradiction to the claims that the Phoebus Cartel gathered to lower the lifespan of light bulbs due to declining sales in a market saturated with long-lasting bulbs. This is cited by some as the birth of Planned Obsolescence. I personally have not be clear on which side of this argument holds more accuracy, but given today's anti-consumer leanings in manufactiring (particulatly in the US), I have my misgivings about it all. https://en.m.wikipedia.org/wiki/Phoebus_cartel https://en.m.wikipedia.org/wiki/Phoebus_cartel

eru 3y ago
Compare https://news.ycombinator.com/item?id=37046713 https://news.ycombinator.com/item?id=37046713

magicalhippo 3y ago

I noticed this early on when I noticed how often I changed the light bulb in the bathroom compared to the hallway where it was always on. Once I thought about it, I assumed it was due to thermal stress.

ekaryotic 3y ago
I'm sure it would be possible to extend bulb life by ramping up the voltage slowly to reduce the thermal stress. not worth it in most environments, but in a bathroom, why not. I understand there are soft start mechanisms used in certain electric motors, i know of an anglegrinder that used one. maybe i could do a transplant some day.
- rocqua 3y ago
  I recently retro-fitted my portable table-saw with a soft-start. The process is quite easy, though the soft-starter you use has to be picked for a certain power-draw. And they might be specific to the type of load (i.e. specific to a universal AC motor) I got my soft-starter from amazon for €10.
- deepspace 3y ago
  A few years ago, I retrofitted my entire house with Lutron Caseta switches, for home automation purposes. The Casetas allow me to soft-start each bulb, and to run lights at less than full brightness most of the time. It would have been interesting to see the effect on incandescent bulb life, but I also took the opportunity to replace all light bulbs with dimmable LCD, so the question is moot.
Ekaros 3y ago
What type of bulbs are we talking about? I could see leds and CFL being affected by moisture in bathroom. Also bathroom could be slightly hotter and worse ventilated than hallway.
- magicalhippo 3y ago
  This was incandescent bulbs. For LEDs the issue is the driver boards, they get crammed into the tiny socket and live a very, very hot life. Doesn't matter that the LED has 100000 hour lifespan or whatever they write on the box when the driver dies after 5000 hours.

pfdietz 3y ago

I don't believe that theory. Instead, I think incandescent bulb lifespan is limited by sublimation of tungsten.

Timon3 3y ago
Do you have a basis for not believing it aside from you having a different theory?
- pfdietz 3y ago
  You will note that incandescent bulbs gradually get dimmer as they age, due to deposition of tungsten on the glass. Also: http://donklipstein.com/bulb1.html http://donklipstein.com/bulb1.html "Due to the high temperature that a tungsten filament is operated at, some of the tungsten evaporates during use. Furthermore, since no light bulb is perfect, the filament does not evaporate evenly. Some spots will suffer greater evaporation and become thinner than the rest of the filament. These thin spots cause problems. Their electrical resistance is greater than that of average parts of the filament. Since the current is equal in all parts of the filament, more heat is generated where the filament is thinner. The thin parts also have less surface area to radiate heat away with. This "double whammy" causes the thin spots to have a higher temperature. Now that the thin spots are hotter, they evaporate more quickly. It becomes apparent that as soon as a part of the filament becomes significantly thinner than the rest of it, this situation compounds itself at increasing speed until a thin part of the filament either melts or becomes weak and breaks." Halogen bulbs last longer because the sublimated tungsten is converted to volatile halides, which then preferentially decompose back to elemental tungsten at the hot spots, healing them.
rcxdude 3y ago
Both are relevant, and can feed into each other. A incandescent lightbulb that has been on for a long time is more likely to fail after a power cycle, as the cycling adds additional stress (anyone who's used them can attest to this: the most common experience with one failing is going to turn it on, only to get a brief flash of light before it fails).

mechhacker 3y ago

This is true for a lot of mechanical devices. For example, turning engines on and off heavily thermally cycles them. It can get worse when they are rapidly cooled or rapidly heated. Jet engines running at constant speed have high cycle fatigue to worry about, but steady temperatures don't pose a thermal stress issue. But shutting the engine off in cold air and letting them go from very hot to very cold suddenly will cause the thicker parts to cool slower than the thin parts, stressing them near the change in thickness. That results in low cycle fatigue (where you can count the cycles to failure in the dozens/hundreds/thousands vs. millions/billions for high cycle fatigue).

Workaccount2 3y ago

I had some recessed lights in my ceiling that I installed in 2000. They worked daily for 20 years before I swapped them out for LED lights. Never had one fail. I attribute it to the fact that the dimmer switch they were on could only do soft turn ons and turn offs. Always took about 3 seconds to turn on and off.