question about household lightbulbs...

[sao123]

since the filament inside a common household lightbulb usually breaks due to thermal and electrostatic stress and the point of powereed on...

theoretically should not a sufficiently cooled bulb never burn out if it was turned on, and left on forever? (assuming nominal power fluctuations only)

 

[CycloWizard]

In a normal incandescent light bulb, the filament is made from tungsten. Like you said, it undergoes large thermal strains because it doesn't start emitting much visible radiation until it reaches ~4,000°F (IIRC). However, since it needs to have such a high temperature to function, you can't really have a 'sufficiently cooled bulb', since it wouldn't emit any light.

So, the way I see it, you're right. If a light bulb were left on forever, it should never burn out. However, in practice, one thing is probably the main contributor to bulb burnout. Cyclic thermal strain (resulting from normal power fluctuations and/or turning the light on and off) fatigues the filament, generally causing it to become brittle. One day when it's heating up, the strain will be too much for it and it will fracture. Alternatively, if you bump it after it becomes brittle, it breaks.

I think this is probably true because of a couple anecdotal observations. At school, we always had lights outside that were constantly on (safety measure in university-owned housing ). These bulbs seemed to go out a lot faster than the indoor bulbs, despite the fact that they were always left on. This indicates to me that fluctuations in the bulb temperature (which could be caused by something as insignificant as a small change in the wind speed) cause rapid thermal strain cycling, leading to faster filament embrittlement. The indoor bulbs generally seem to go out after a long time when someone bumps them even very lightly. The filaments seem to be more sturdy after only being in use for short periods.

To solve this problem, we could use a material that has a near-zero coefficient of thermal expansion (CTE), as this would minimize thermal strain. However, not very many of these materials exist, and most that do don't seem to emit light when heated. The one that comes to mind is a carbon fiber-polymer composite. The carbon fiber actually has a negative CTE, so when it's mixed with a polymer with a positive CTE, they can cancel each other out if everything is done correctly. However, it doesn't matter how hot you heat it - it's not going to spit out any light for you.

Other alternatives would be to make the bulbs bigger or change out the argon filling with a less thermally conductive gas. This would insulate them from changes in ambient temperature and theoretically improve their life expectancy if my theory is correct.

HowStuffWorks.com article on light bulbs

 

[dkozloski]

Many moons ago light bulbs were filled with a vacuum and the filament was much more sturdy. It took more current to operate the bulbs but they lasted nearly forever. I have some bulbs in my house that were installed before 1967 that still operate. I know they have been in this long because they still have some residue on them from when they were submerged in our flood of 1967. What strikes me is that the quality control of current bulbs is so precise that if you replace say, four bulbs in the light strip above the bathroom sink together, they will all fail within days of each other.

 

[AnthraX101]

I'm surprised no one posted a link to the Centennial Bulb yet. Burning since 1901.

AnthraX101

 

[hemiram]

I have a weird thing going on in my house. We have pretty high line voltage, 125V on average. Some light bulbs in particular sockets last a long time, some hardly any.

The oddest one is the back porch. I wrote on the base, 1/14/02, the last time I changed it. I changed it last week, and it was just over 4 years old. They usually last about 4-5 years. On the front porch, the lifespan is insanely short. If a bulb lasts 6 months, it's a rarity, usually 3 months is it. The back porch light is on at least 3X what the front is, and a voltmeter confirms the voltage is almost exactly the same. They are in identical fixtures, and are both exposed to wind, but the back porch is rained on, and the front porch is covered by the roof.

The same thing goes on in the garage. There are two standard light sockets on the garage ceiling, facing down. A bulb on the left side lasts a couple of years, mimimum, but the right side eats bulbs at a one a month or maybe two a month rate. They are on the same switch, and the voltage measures the same. I put two of those "five year guaranteed" flourescent replacements in there a couple of years ago, and the right one blew at about 6 months, the left one just went a few days ago.

It's just weird, and annoying. The front porch fixture is a bitch to get open. it's warped slightly. It closes up fine though.

 

[herm0016]

temp and electro static forces contribuite to burning out of the light bulb but the real reason is that that filiment emits its own atoms along with the radiation. ever see a small bulb that has burnt out? the tungston is all over the glass evelope. this happins with all lightbulbs, the filiment gets small in diameter as you use it. this is also the reason they seem to get dimmer over the life of the bulb. the tungston coats the inside of the glass envolepe. we have issues with this in the theater i work in, when the lamps in our insterments start to get dim and produce a different color of light we must change them.

 

[dkozloski]

The brightness of the light emitted is limited by how quickly you can stand the evaaporation of the filament, among other things. The idea behind quartz-iodine (halogen) bulbs is the addition of the iodine forces the evaporated filament atoms to return back to the filament instead of plating the glass. Quartz is used for the envelope because it can withstand the higher temperatures.

 

[t0kinl3lunts]

You can obviously design bulbs that would last over 100 years for a reasonable price, whoever makes it will run out of customers pretty fast tho. Tungsten is a decent fillament material only because its so cheap and burns out at such a constant rate that they can market them perfectly.

hemiram, did you also check the amps? how about the sockets themselves? could any of the wiring in the circuits be old and possibly shorting them prematurely?

 

[alpha88]

I think someone mentioned this - we can make bulbs that last for much longer than current bulbs, but the manufactures have no motivation to do so - if they did, they'd kill their market.

 

[silicon demon]

the weird variations you're seeing in your bulbs are probably due to one simple factor: the mechanical connections.

the fixture sockets themselves are very thin metal, and get tweaked easily; so in two different fixtures you have slightly different levels of resistance (ahead of the bulb's element). what this does is cause current to rise. you already have high voltage (125v); so it's this resultant increase in current flow (not the voltage itself), that diminishes the life of your bulbs.

and it's the different resistive values (which affect current flow) in the porch lighting fixtures , that make one tend to fry a bulb sooner than the other.

i'd say that's a highly probable answer to your question.

 

[irwincur]

I think someone mentioned this - we can make bulbs that last for much longer than current bulbs, but the manufactures have no motivation to do so - if they did, they'd kill their market.

We have them. Compact flourescents. However, they did account for the longer life - they charge 3 - 5x more for them...

Bastards.

 

[smack Down]

Originally posted by: silicon demon
the weird variations you're seeing in your bulbs are probably due to one simple factor: the mechanical connections.

the fixture sockets themselves are very thin metal, and get tweaked easily; so in two different fixtures you have slightly different levels of resistance (ahead of the bulb's element). what this does is cause current to rise. you already have high voltage (125v); so it's this resultant increase in current flow (not the voltage itself), that diminishes the life of your bulbs.

and it's the different resistive values (which affect current flow) in the porch lighting fixtures , that make one tend to fry a bulb sooner than the other.

i'd say that's a highly probable answer to your question.

More resistance will reduce the current flowing to the bulb and increase the life span. The person is having very short life spans so i don't think that is the issue.

 

[feralkid]

Originally posted by: hemiram
I have a weird thing going on in my house. We have pretty high line voltage, 125V on average. Some light bulbs in particular sockets last a long time, some hardly any.

The oddest one is the back porch. I wrote on the base, 1/14/02, the last time I changed it. I changed it last week, and it was just over 4 years old. They usually last about 4-5 years. On the front porch, the lifespan is insanely short. If a bulb lasts 6 months, it's a rarity, usually 3 months is it. The back porch light is on at least 3X what the front is, and a voltmeter confirms the voltage is almost exactly the same. They are in identical fixtures, and are both exposed to wind, but the back porch is rained on, and the front porch is covered by the roof.

The same thing goes on in the garage. There are two standard light sockets on the garage ceiling, facing down. A bulb on the left side lasts a couple of years, mimimum, but the right side eats bulbs at a one a month or maybe two a month rate. They are on the same switch, and the voltage measures the same. I put two of those "five year guaranteed" flourescent replacements in there a couple of years ago, and the right one blew at about 6 months, the left one just went a few days ago.

It's just weird, and annoying. The front porch fixture is a bitch to get open. it's warped slightly. It closes up fine though.

Have you tried using 130w bulbs?

 

[Rubycon]

Originally posted by: irwincur

I think someone mentioned this - we can make bulbs that last for much longer than current bulbs, but the manufactures have no motivation to do so - if they did, they'd kill their market.

We have them. Compact flourescents. However, they did account for the longer life - they charge 3 - 5x more for them...

Bastards.

CF lamps are more complicated and require a driver or ballast which makes the manufacturing cost higher. They also rarely last as long as they claim unless you purchase trustworthy brands.

 

[hemiram]

Originally posted by: feralkid

Originally posted by: hemiram
I have a weird thing going on in my house. We have pretty high line voltage, 125V on average. Some light bulbs in particular sockets last a long time, some hardly any.

The oddest one is the back porch. I wrote on the base, 1/14/02, the last time I changed it. I changed it last week, and it was just over 4 years old. They usually last about 4-5 years. On the front porch, the lifespan is insanely short. If a bulb lasts 6 months, it's a rarity, usually 3 months is it. The back porch light is on at least 3X what the front is, and a voltmeter confirms the voltage is almost exactly the same. They are in identical fixtures, and are both exposed to wind, but the back porch is rained on, and the front porch is covered by the roof.

The same thing goes on in the garage. There are two standard light sockets on the garage ceiling, facing down. A bulb on the left side lasts a couple of years, mimimum, but the right side eats bulbs at a one a month or maybe two a month rate. They are on the same switch, and the voltage measures the same. I put two of those "five year guaranteed" flourescent replacements in there a couple of years ago, and the right one blew at about 6 months, the left one just went a few days ago.

It's just weird, and annoying. The front porch fixture is a bitch to get open. it's warped slightly. It closes up fine though.

Have you tried using 130w bulbs?

130W?? You mean 130 volt? No, I would guess the extra cost would wipe out any savings I would get versus buying bulbs on sale. I have an LED replacement that's going into the garage today, it was 20 bucks. If it lasts even a couple of years, I will be ahead.