Shouldn’t the vacuum insulate the glass from the heat of the burning filament?
Same way sun heats the earth
3 forms of heat transfer
Conduction. Transfer of heat from one medium to another.
Convection. Transfer of heat within the same medium.
Radiation. Non-contact transfer of heat.
Vacuum means no convection heat. It however does not mean no radiation heat. The filament radiates heat through vacuum the same way the sun does.
Additionally, theres not vacuum in buldbs, but inert gas, like argon.
There no longer is a vacuum in bulbs, but there was for a very long time.
“Halogen” bulbs are just incandescent bulbs filled with inert gas and a small amount of bromine or iodine. Very interesting chemistry https://en.wikipedia.org/wiki/Halogen_lamp
Maybe they are thinking of how mugs and thermoses can be labeled “vacuum sealed,” and that the marketing implies that the vacuum between the walls insulates the outer wall (where the hand touches) against the heat.
And those are usually made out of some metal, that’ll do pretty good reflecting radiation heat transfer
for better insulation you can put more reflecting layers inside. i’ve heard of insulation for liquid helium pipe, it used thousands of layers of aluminized mylar between two tubes in vacuum. it’s one barrier between 4.2K and room temperature, and it works good enough to be used in helium manufacturing plant
You ever seen those vacuum ovens too? Kinda doing the opposite, only letting radiation in, but from just solar radiation I’ve heard in sub zero temps they can get to a constant 500 F. Wonder what one would be capable of with some one way mirror type refraction to keep all that shit in
Vacuum is an absence of stuff. What would be insulating the glass? Air would be an insulator; a vacuum wouldn’t do shit.
Think of heat like a physical object. It can travel through a vacuum unimpeded. There is nothing within a vacuum to stop the heat traveling through it. But if there was even just a thin atmosphere, it would collide with some of those molecules and not reach the glass, taking longer for the glass to get hot.
It’s a bit more complicated than that since in reality the air will also be heated and transfer that heat, but just for the purpose of how vacuums work, we can ignore all that.
