Neon lamps are lamps that contain noble gases... They light due to the presence of energetic levels for electrons (according to the definition of it in books). But I don't understand yet why noble gases are used in such lamps. Any help please?
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$\begingroup$ there isn't much gases to begin with, and many complex ones may dissociate under electric discharge, producing solid deposits and degrading the color (carbon derivitives) or even react with parts of the tube even if producing a nice color (halogens) $\endgroup$– permeakraOct 26, 2015 at 18:49
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$\begingroup$ A) to get the desired color (possibly in conjunction with a phosphor coating), B) stability, C) cost. $\endgroup$– Nick TOct 26, 2015 at 22:40
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Strictly speaking "neon" lamps contain neon but the term is often used colloquially for a whole range of coloured lighting probably because the red neon tubes are one of the commonest.
But it isn't just noble gases that are used, though they are the most common. Carbon dioxide is sometimes used. And there are many discharge lamp that add metals or metal salts, though these are more common in other uses such as high intensity street lighting.
The noble gases and mixtures of them are commonly used in coloured advertising lighting because they offer a range of colours in a simple low-pressure discharge lamp without the added complexity of fluorescent coatings (as in common fluorescent tubes) or high-pressure systems (as is required in high intensity systems used in street or industrial lighting). Advertising signage often consists of long glass tubes in custom shapes and the simplicity of simple gas discharge makes the results cheaper than more sophisticated alternatives.
The colours are derived from the energy levels of the electrons in the gases and it just so happens that the range of those energy levels in noble gases correspond to a useful variety of colours.
There is a good summary of the colours (and other types of discharge lamps) in this Wiki article.
answered Oct 26, 2015 at 18:36
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2$\begingroup$ You sort of missed the question. It is a combination of factors. Yes noble gases have excited states which fluoresce with colors. But also noble gases are relatively chemically inert. So the ions convert back to uncharged atoms without chemically reacting with the electrodes or the container (glass tube). $\endgroup$– MaxWOct 26, 2015 at 19:01
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$\begingroup$ @MaxW I'm not sure this is major factor at all. There are plenty of discharge lamps that use non-noble gases, metal vapours or salts but most are not as simple or convenient to operate. $\endgroup$ Oct 26, 2015 at 19:05
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$\begingroup$ I understood the cause of using noble gases, but I got confused because their justification was because they are inert gases. Really, I don't know what does it mean to have an inert gas. I just got to study that the family of column 18 is inert or noble gases and nothing else. $\endgroup$ Oct 26, 2015 at 19:23
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3$\begingroup$ @user225430 - Noble gases for practical purposes don't chemically react with anything. "practical purposes" means barring exotic laboratory conditions. Thus the atom is the "molecule". Thus my sentence "So the ions convert back to uncharged atoms without chemically reacting with the electrodes or the container (glass tube)." You could get a gas discharge through oxygen, but the oxygen atoms and ions would react with the metal electrodes to form metal oxides. $\endgroup$– MaxWOct 26, 2015 at 19:38