On Wed, 14 Nov 2007, Chris Swinson wrote:
One thing I noticed with flu-tubes, that if you walk away from the coil
slowly, it goes dim, but just before it goes out totally the light
alternates inside the tube, such as 1" on, 1" off.. all the way up the
tube..
That's called "positive column striations," and fluorescent tubes always
have them all the time... but usually they're vibrating back and forth too
fast to notice. If you have a straight piece of clear neon sign tube,
and sweep it rapidly back and forth while lit, then you can see the moving
patterns. They're also called "jellybeans" by neon sign makers. With
just the right gas mixture and high-freq power supply you can create
stable ones in a neon sign, so the sign is made of "dotted lines."
I wonder if sparks at one ATM also have them. If the blotches are moving
around fast, we might never realize that they exist. (View sparks with a
spinning mirror and look for swerving stripy patterns.)