[TheForge] Shop Lighting

[Bruce Freeman]

Corona results from a high electric field.  Similar, if not identical, to what's going on in the fluorescent tube.  However, I think of corona as an effect around a sharp point or very thin wire, at atmospheric pressure.  A fluorescent tube is at reduced pressure, so an arc is easier to draw (vacuum having less resistance than unionized air) - I think.  The glow around a corona is typically the nitrogen glow, but may have an oxygen component.  In either case, there's UV present, so take care.  And ozone is produced, which is not good to breathe.

What's going on in a neon tube is essentially the same thing.  The difference matters to a chemist or physicist, but not to a layman.  Namely, nitrogen absorbing energy from an arc promotes an electron in a molecular orbital to a higher-energy molecular orbital (I'm pretty sure).  Whereas, neon absorbing energy from an arc promotes an electron in an atomic orbital to a higher-energy atomic orbital.  Real important difference, huh? 

The reason that nitrogen emits UV and neon emits red is that the difference in energy between the two molecular orbitals of nitrogen happens to correspond to UV (high energy), whereas the difference in energy between the two atomic orbitals of neon happens to correspond to red light (low energy).

Bruce

>>> grover.richardson at gtri.gatech.edu 3/1/2006 11:51:26 AM >>>
Hmm.  Clearing up my understanding.

Neon breaks down with a gas discharge.  Whereas nitrogen glows in the UV due
to high Voltage breakdown and/or corona??  We get corona all the time around
here so am used to seeing it.

>*>-----Original Message-----
>*>From: theforge-bounces at mailman.qth.net 
>*>[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Bruce Freeman
>*>Sent: Wednesday, March 01, 2006 11:29 AM
>*>To: theforge at mailman.qth.net 
>*>Subject: RE: [TheForge] Shop Lighting
>*>
>*>
>*>Well, that 's not completely true.  Yes, neon is a noble gas 
>*>(a monoatomic gas with almost no tendency to react with 
>*>anything else).  But nitrogen glows in the UV and is not a 
>*>noble gas.  It IS a very stable molecule, though, so maybe 
>*>that helps. 
>*>
>*> But such gases might be chosen simply because they'd be 
>*>less corrosive to the electrodes.  If you used oxygen in the 
>*>tube, it would probably chew through the electrode in no time.
>*>
>*>Bruce
>*>NJ
>*>
>*>>>> grover.richardson at gtri.gatech.edu 3/1/2006 10:58:17 AM >>>
>*>Yes.  If you look at a red "neon sign," you can actually see 
>*>inside the bulb and see the glowing gas.  As I remember it, 
>*>neon glows red and other gasses glow different colors.  Only 
>*>certain gasses will glow, I think they are called the "noble 
>*>gasses."  It's been a loooong time<G>.
>*>
>*>Fun stuff.
>*>
>*>And back to hammering on something else<G>.
>*>
>*>
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