Heating a tungsten filament to find out the maximum brightness emitted

[Slimy0233]

TL;DR

If we heat the filament of a light bulb sufficiently and hold it in a confined place by placing restrictions using magnetic fields, how bright can the light get?

I was taking notes from a lecture on Quantum Physics and during the introduction, they gave an example of what led to the discovery of Quantum Physics: The electric bulb example where the brightness and colour of light depended on the temperature of the filament(see: https://www.britannica.com/science/Stefan-Boltzmann-law). At certain temperatures, the colour of the light emitted will cease to turn any bluer(at Yellow White), but what happens to the brightness? What is the maximum brightness a filament can achieve before turning into liquid or plasma and after turning into liquid (if we find some way to hold it together and heat it).
PS: I realize that the theoretical limit is quite large, so large in fact, that it would only stop when it creates a black hole, but I am concerned about the practical limit.

 

[Baluncore]

Welcome to PF.

You need to include time in your model, and accept that the filament structure will be lost once the lamp is operating. As the filament temperature becomes greater, the hot metal filament evaporates faster, until it becomes a metal plasma discharge lamp. Radiation from the metal plasma will contain characteristic lines at wavelengths determined by the ionized metal used to fabricate the filament. Alloys melt at lower temperatures than their pure metal elements.

The pressure inside the envelope will increase rapidly until the envelope fails. At some point, the glass envelope will melt if it has not shattered due to the thermal shock earlier.

PS: I realize that the theoretical limit is quite large, so large in fact, that it would only stop when it creates a black hole, but I am concerned about the practical limit.

Black holes are massive objects, while a hot star is a more diffuse object. Our Sun contains many metals in its plasma. You can answer your own question by asking a similar question: What is the brightest and hottest type of star that has not yet evaporated into the surrounding space?

 

[DaveE]

This is kind of an engineering question. How will you contain or control a tungsten plasma with a huge amount of current flowing. Back in the day, I worked on very high power Ion lasers; that Ar plasma inside the laser tube* was really bright!! The limits for us were practical: cooling, mechanical strength, power available, magnetic containment field strength, etc. I suppose if we were scientists and not equipment manufacturers we could have made it brighter, but that wouldn't have suited our needs. Often this sort of thing is ultimately limited by how hard you'll try, who will pay for it, etc.

* About 50KW discharge in a <1cm dia. x 1m long arc for our big laser.

 

[anorlunda]

TL;DR Summary: If we heat the filament of a light bulb sufficiently and hold it in a confined place by placing restrictions using magnetic fields, how bright can the light get?

At certain temperatures, the colour of the light emitted will cease to turn any bluer(at Yellow White), but what happens to the brightness? What is the maximum brightness a filament can achieve before turning into liquid or plasma and after turning into liquid (if we find some way to hold it together and heat it).

Thomas Edison's lab investigated for years different materials that would not burn out the filament so fast. Not all of them were metals. Bamboo was the leader for a long time.

Evaporation was not the only failure mode. Embrittlement, differential expansion, and corrosion were also factors.

 

[DaveE]

This is kind of an engineering question. How will you contain or control a tungsten plasma with a huge amount of current flowing. Back in the day, I worked on very high power Ion lasers; that Ar plasma inside the laser tube* was really bright!! The limits for us were practical: cooling, mechanical strength, power available, magnetic containment field strength, etc. I suppose if we were scientists and not equipment manufacturers we could have made it brighter, but that wouldn't have suited our needs. Often this sort of thing is ultimately limited by how hard you'll try, who will pay for it, etc.

* About 50KW discharge in a <1cm dia. x 1m long arc for our big laser.

Oops! I missed the part about BEFORE it melts.

It's a much more interesting question your way. IDK.

 

[Slimy0233]

Thomas Edison's lab investigated for years different materials that would not burn out the filament so fast. Not all of them were metals. Bamboo was the leader for a long time.

Evaporation was not the only failure mode. Embrittlement, differential expansion, and corrosion were also factors.

> Bamboo was the leader for a long time
Damn! that's some interesting fact!

 

[Slimy0233]

Welcome to PF.

You need to include time in your model, and accept that the filament structure will be lost once the lamp is operating. As the filament temperature becomes greater, the hot metal filament evaporates faster, until it becomes a metal plasma discharge lamp. Radiation from the metal plasma will contain characteristic lines at wavelengths determined by the ionized metal used to fabricate the filament. Alloys melt at lower temperatures than their pure metal elements.

The pressure inside the envelope will increase rapidly until the envelope fails. At some point, the glass envelope will melt if it has not shattered due to the thermal shock earlier.Black holes are massive objects, while a hot star is a more diffuse object. Our Sun contains many metals in its plasma. You can answer your own question by asking a similar question: What is the brightest and hottest type of star that has not yet evaporated into the surrounding space?

thank you for your answer.
Can you elaborate on "hot star is a more diffuse object" and also, black holes are indeed normally massive, but we can create black holes which aren't massive too, so I don't understand your point. If the energy density becomes high enough it will form a black hole, right?

Ok, trying to understand the diffuse object point, if the energy density becomes high enough, will it even be able to diffuse before forming a black holes? God, I think I am not knowledgable enough to understand your well-made point. I will ask chatgpt lol ;)

 

[Slimy0233]

This is kind of an engineering question. How will you contain or control a tungsten plasma with a huge amount of current flowing. Back in the day, I worked on very high power Ion lasers; that Ar plasma inside the laser tube* was really bright!! The limits for us were practical: cooling, mechanical strength, power available, magnetic containment field strength, etc. I suppose if we were scientists and not equipment manufacturers we could have made it brighter, but that wouldn't have suited our needs. Often this sort of thing is ultimately limited by how hard you'll try, who will pay for it, etc.

* About 50KW discharge in a <1cm dia. x 1m long arc for our big laser.

So again, I guess, the limits are practical as you said, and I think it hasn't been found out before. Thanks! I just wanted to write it in my notes and I was having this question and I didn't know what to write.

 

[Baluncore]

If the energy density becomes high enough it will form a black hole, right?

No.
You and the classical physics experiment would be destroyed before any BH became involved.

The release of energy causes the filament and the supports to expand explosively. That is more like a bright star that radiates and rapidly evaporates, to become a plasma in space.

 

[DaveE]

TL;DR Summary: If we heat the filament of a light bulb sufficiently and hold it in a confined place by placing restrictions using magnetic fields, how bright can the light get?

At certain temperatures, the colour of the light emitted will cease to turn any bluer(at Yellow White), but what happens to the brightness?

This is essentially blackbody radiation. The answer to you spectral density questions are well described in literature. Brightness may need more definition, like, over which wavelength(s). But again it's well described. In any case hotter equals brighter if you are measuring over a wide bandwidth, So, your question about maximum brightness before it melts is synonymous with the question about maximum temperature before it melts. This is a materials science question that is well above my ability. Frankly, I'm not even sure what the "melting" phase transition really means at the atomic level.

Of course, in the engineering world, you'll want to work well above, or below, that phase transition. How you hold a solid filament is much different than liquids or plasma. You can also get more radiation by increasing the amount of hot Tungsten in the filament. But, again, there are questions about what exactly you mean by "brightness".

BTW, I've never heard of an application that used high brightness incandescent liquids. Has anyone else? It seems to me you'd want to jump right up to a plasma discharge.

PS: things like dye lasers don't count. I mean excitation by electrical discharge.