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Re: novelty bulb



Ne-2 's do. the voltage necessary to initiate discharge depends on the geometry,
electrodes, filling, and its pressure. Many Hg and Na lamps contain another gas
in order to heat the metal 'till its greater conductivity "takes over", otherwise
they use a heater. Harnwell (Principles of Electricity and Electromagnetism)
discusses this well. I his discussion explains the constancy of the glow
thickness independent of the geometry. Under cold cathode discharge, check out
cathode fall, Crooks and Faraday dark spaces, and the negative glow.

Until the advent of SS electronics gas tube regulators were common. e.g.: 0A2,
0A3, 0B3, 0C3, 0D3, etc. Their ignition V varies from ~ 105 V to 185, and their
operating V's ~ 75 to 150 V.

bc



Brian Whatcott wrote:

At first glance, this looks like a variant of the neon (?) flicker candle lamp
which can be bought in small or regular edison screw fittings.
Neon strikes at about 80 v
I take it that thermal trtansport of the ionised medium enhances
the flicker effect, which I find attractive.

Brian

At 11:28 AM 7/24/02, you wrote:
Greetings,

While shopping at a Target location last week for a low-budget ($20)
plasma ball, I noticed another novelty bulb ($4) on the rack. It looks
like a regular clear incandescent light bulb, except that in place of a
tungsten filament there are electrodes (in the shape of stars and the word
"party!") some colored white and some black. The white pigment appears to
have been sloppily applied as a paint by a brush, while the black pigment
is a uniform coating.

When screwed into a 120V AC socket, the black electrodes glow with a
neon hue with a 1mm to 2 mm discharge aura while the white prongs glow
pale green with no discharge aura. A closer look at the glass base within
the bulb reveals that one of the white/green prongs is not connected to
the circuit, and so must glow due to absorption of UV or xrays emitted by
the orange electrodes. There are no plasma "streamers' produced.

I find it curious that

1. the discharge glow is produced at such a low voltage, compared to the
2000 volts in a gas tube ballast.

2. the orange glow around the elctrodes is uniform across the length of
the 40 mm wide electrode, even though its separation from the other
electrode varies from about 4mm to 20mm.

3. there is no discharge 'ray' between the orange electrodes at their
point of least (4 mm)separation.

Has anyone else looked at these bulbs?

Thanks,

-Barry Gragg

The Dwight School

NY, NY

Proud Home of the 2002 NYC Science Olympiad Cowabungee and Physics Lab Champs!



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