Why is argon better than a vacuum?

[eurekameh]

Argon gas is used in a lightbulb because it's not reactive, whereas air is. But why is it better than a vacuum?

 

[Algr]

My guesses:
1) If there is pressure inside the bulb, you don't need the glass to be as strong.
2) The gas will conduct heat away from the filament, cooling it down. (I'm not sure this is a good thing though.)

 

[Bill_K]

Prolongs the life of the filament.

 

[pallidin]

Argon gas is used in a lightbulb because it's not reactive, whereas air is. But why is it better than a vacuum?

A near perfect vacuum would be required. Argon is non-reactive and replaces the air.
Basically, it's a manufacturing cost/benefit ratio type of thing.
Argon infusion is cheaper than vacuum.

 

[DaveC426913]

Doesn't the partial pressure also discourage the bulb coating and filament materials from slowly evaporating, as they would tend to do in a vacuum?

 

[Curl]

vacuum will also cause the shell to shatter under the atmosphere

 

[KingNothing]

vacuum will also cause the shell to shatter under the atmosphere

Why would you say that? Bulbs are actually very good at withstanding pressure differentials. In fact, up until about 1913, light bulbs were manufactured with a vacuum (or at least as close as they could come).

Today, most bulbs are pressurized at about 0.7 atmospheres at room temperature to accommodate for expansion as the bulb heats.

 

[Mapes]

Ding ding, DaveC426913 wins. The primary need for an internal gas is not structural but to prevent the filament from evaporating and coating the inside of the bulb with a thin layer of opaque metal. With some partial pressure (ideally from an inert gas so as not to react with the filament), any metal atom that evaporates from the filament will get bounced right back instead of traveling, line-of-sight, to the glass. http://books.google.com/books?id=a6...resnum=1&ved=0CDcQ6AEwAA#v=onepage&q&f=false"

 

[nksq]

2) The gas will conduct heat away from the filament, cooling it down. (I'm not sure this is a good thing though.)

Not trying to be pedantic, just learning physics, and this is a bit of a derail, but wouldn't this heat transfer be primarily convection and not conduction?

 

[Curl]

Why would you say that? Bulbs are actually very good at withstanding pressure differentials. In fact, up until about 1913, light bulbs were manufactured with a vacuum (or at least as close as they could come).

Today, most bulbs are pressurized at about 0.7 atmospheres at room temperature to accommodate for expansion as the bulb heats.

Really? Try blowing glass with a perfect symmetry. Then ding it against the table and see what happens if there is a vacuum inside.
Also, let the filament heat the glass up and then hang it from a wall and see what creep is.
There is also diffusion which means a vacuum won't stay long. In 1910 the bulbs were made thick, it was pretty much a jar with a wire in it. Now they're trying to save money and are 400 microns thick in some cases.

The no.1 reason is what Dave said, but I wasn't going to repeat it and was just offering another reason why Argon is good.