Shouldn’t the vacuum insulate the glass from the heat of the burning filament?
In addition to the stuff everyone else is saying, most modern bulbs don’t have a vacuum at all.
Most modern bulbs are filled with an inert gas like argon or xenon. Usually at a lower pressure (around 70% of standard atmospheric pressure), but nowhere near a vacuum.
This has, while inert to chemical reaction, is more than capable of transferring heat.
Why does the sun heat the Earth if space is a vacuum?
Because of me. Whenever I look up at the sun, I think about the inevitable supernova which the sun sooner or later will turn into. This in turn gives me anxiety and makes me sweat a lot, which heats the earth.
God’s will
Who?
Ooooh risky
Same way sun heats the earth
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.
In addition to what others have said, they’re not a vacuum inside. They’re filled with 0.7 atm of argon gas. That would slow the transfer of heat, but there’d still be plenty of heat transfer through convection.
Why not 1 atm?
Several reasons. But I would guess a big part is that air pressure drops with altitude. 1atm is the pressure at sea level. According to my google-fu the air pressure on Mt Everest is a mere 0.33 atm.
You don’t want your light bulb exploding when it breaks, especially if part of the reason you put a special gas in it was to prevent it from imploding when it breaks.
Now of course most people live significantly closer to sea level than to the peak of Mt Everest, but if a gas is heated in an enclosed space, its pressure rises.
Also, if you have to choose between shards tending to go inwards or outwards when the bulb shatters, you’d probably prefer them tending to go inwards, provided it’s not so fast they shoot past the middle as they would with a much lower pressure.
Lastly, it saves on gas.
Assuming an ideal gas, going from 20 C to 100 C at constant volume brings you from 0.7 atm to 0.9
Tracks better with my assumption than expected.
