Date: Mon, 08 Apr 2002 13:40:53 -0400

Author: Bill McNairy

Subject: RE: Rotating Light Bulb

Post:

I was playing with 120 V on this idea the other day. I purchased a
couple of the glowing ghost light bulbs at the dollar store for $1 each:
they seem to have two ghost shaped electrodes about .3-.5 cm apart from
each other in an otherwise normal glass bulb and base for a 120V light.
When turned on, the bulbs glow orange- BOO! When the bulb is moved
back and forth in a darkened room, the 'ghost image ;-)' of each plate
persists in the vision as a series of lit dashes. Fun to observe and
doesn't require additional wiring or exposure to 120 VAC-- just screw in
a bulb into a small base attached to a long cord and move back and
forth. BTW-- the bulb is rated at 3 W, so it does not heat up quickly.

Even better!! I just switched in a flower and petal bulb purchased on
sale earlier at Spencers gifts: Neo FX light bulb from Luma series
"orchid bulb" (priced at $5.99, sold for $3.96). This has a pair of
flowers mounted at different heights on different electrodes. At the
base of each electrode is attached a leaf- when turned on the flowers
have a blue/purple haze about them and the leaf surfaces are bright
green. Lots of physics here:

1. The flowers are ionizing the gas near them into a plasma. "Capture
all of the wonder and classic beauty of sensual neon with our exciting
collection of unique light bulbs" reads the blurb on the box-- love the
advertising. I verified this by using a small tesla coil that ionized
the gas near the bulb wall: the glow appeared at the glass bulb as well
as on the surface of the flowers. Electrons appear to be coming from
the - plate and hitting gas molecules as they move to the + plate,
thereby creating the glow only about one of the plates (the + one where
the electrons would be moving the fastest??).

2. The leaves are not ionizing the gas into a plasma-- they glow
because they are coated with a green phosphor. The plasma must be
making some UV because the leaves are very bright-- but their color is
from the surface only with no ionized plasma around the leaf.

3. When the bulb is moved back and forth in a darkened room you can
easily see the follwing: upper flower on-- both off-- lower flower on--
both off. This shows the polarity and the variation of the AC voltage.

Cheap and neat demos at little cost or danger. I still want to build
the bicolor one with AC/DC power supplies....

bill

--
*****************************************
William W. McNairy, Ph. D.
Lecturer
Room 104I (919)-660-2689
Dept. of Physics, Duke University
Box 90305 Durham, NC 27708
*****************************************

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