Re: Why is Ar or N2 used in tungsten filiment light bulbs?

N2 is not used in light bulbs.  It is too reactive.  Ar (Argon) and another
member of Ar's chemical 'family' (Krypton, Kr) are used in light bulbs.

Light bulbs pass electric current through a coiled tungsten wire (the symbol
for Tungsten is W, from the old name for the element, Wolfram).  Tungsten is
capable of withstanding high temperatures and has a high melting point
(which can be found in a chemical handbook or on a periodic table).  So, in
the light bulb, the tungsten is heated to a high enough temperature so that
it gives off light.  In the presence of air (mainly N2 and O2) tungsten
heated to the required temperature to give off light would react with O2 and
oxidize. This temperature would also be high enough for the tungsten to
react with  nitrogen (N2 is not as reactive as O2, but at a high enough
temperature it WILL react).  Gasses on the right side of the periodic table
(He, Ne, Kr, Ar) are not very reactive (under some 'strange' conditions they
will react, but that's another story). Historically these gasses were not
observed to react with anything.  In a sense they seemed to be 'above' the
need to react with other elements.  For this reason they were called Noble
gasses. If one heats tungsten in these gasses, so it will give off light, it
will not react (burn up), or reacts VERY slowly.  I think that Ar or Kr are
used in light bulbs rather than He or Ne.  I'm not sure why this is the
case.  Perhaps the tungsten lasts longer in these gasses rather than the
others.  To find out more, the questioner can go the web sites of General
Electric, Sylvania, or Philips.  Maybe these sites discuss light bulb
manufacturing.

Dan Berger adds:
Ar is most commonly used in lightbulbs for several reasons:
1. Argon is the cheapest of the noble gases; it can be distilled from liquid 
air. Krypton is not too much more expensive.
2. Helium and neon are lighter than air, while argon and krypton are heavier 
than air. This makes argon and krypton easier to use to fill bulbs; you can 
just pour it in!
3. The atoms of helium and neon are smaller than argon and krypton; this makes 
helium and neon more likely to diffuse out of the light bulb (and be replaced 
with air, which is too reactive).