What gas is in lightbulbs

 
 

While all lamps were pumped out in the first decades of incandescent lamp manufacture, today it is only the lamps with low power, for example 25 W lamps or "bulbs" for bicycle lights.
All incandescent lamps for higher power e.g. 60 W, 100 W are filled with gas, mostly a mixture of 93% argon and 7% nitrogen. There is a compelling reason for this technique.

 

The decisive factor is how much the metal evaporates. If the pressure in the evacuated glass bulb is close to zero, the metal atoms escape from the wire much more easily than if a gas with normal pressure or even overpressure is present in the vicinity of the wire.
In the early incandescent lamps, metal evaporation was therefore relatively high, and a dark layer formed on the inside of the glass bulb, which naturally weakened the light. Only with the lamps with low power is the effect not so important, since the temperatures are not so high here.

If there is a gas with a certain pressure around the wire, the escape of metal atoms from the wire surface is inhibited and evaporation is less.
However, a new problem now arises: while the vacuum insulates the heat well, the filling gas dissipates heat. The heat on the wire should not be lost, because it is needed there so that the wire glows brightly.
This problem was only solved by further development. The tungsten wire was wound into a fine spiral - the so-called incandescent filament.

 

You even do this twice, so that the spiral is wound again into a larger spiral - the double spiral. In this way, the wire is packed very compactly into a narrow space. The gas can thus remove less heat and the coils heat each other up.

The double helix
 

Long lifespan or great brightness?

 
In today's construction, incandescent lamps are designed for a service life of 1000 hours. This is a compromise, since you have to choose between lower temperature, i.e. lower luminous efficacy and long service life, and higher temperature, i.e. greater luminous efficacy but shorter service life.