Re: Fluorescent light - standing waves

[Bernard Cleyet <anngeorg@PACBELL.NET>]

I think the tube may have leaked * so the distance electrons must travel
to gain sufficient KE to ionize the gas has increased.  If I remember
from the distant past when I played with long tubes, such behavior is
common in partially evacuated tubes with high voltage applied to the end
electrodes.  The features are named, e.g. Crooks dark space, cathode
glow, Faraday dark space, positive column, etc.  I've noticed the
movement, but w/o further thought I can't add to BW's explanation.
Harnwell points out that sometimes oscillations obscure the striations
in the positive column.

* Also, the emission from the end electrodes may have decreased
resulting in a lower current density.  This would result in loss of a
continuous plasma.

bc

Brian Whatcott wrote:

> At 06:01 PM 1/20/2004,  Franklin Barish, you wrote:
>
>
> > Before changing a fluorescent light bulb that was not going on
> > immediately, I noticed waves (dark and light regions with the light
> > regions about 3 times larger than the dark ones) moving slowly across
> > the 30 inch bulb. The wavelength was about 2 inches and the set of
> > waves were moving slowly to the right.
> >
> > Please explain.
> >
> > Frank
> > --
> > Dr. Franklin Barish
>
>
> I see that there was no undue haste in responding to your  question,
> Franklin,  and apparently I should not be surprised, in that plasma
> dynamics are not yet thoroughly investigated.
>
> The gas mix in a low pressure argon or neon  or krypton fill
> fluorescent tube filling with a mercury trace can be expected
>  to vary slowly in time due to sputtering effects at the electrodes
> and walls possibly capturing some of the more active component.
>  While ionization is a fast process, the slow ionic movement and
> faster electron transport are sometimes described as having two
> temperatures, and I speculate that it is in the ion recoil from
> electron impact near the tube wall that an explanation of
> "crawling plasma" will at length be offered.
>
>
> Brian Whatcott    Altus OK    Eureka!