Re: fluorescent tube question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

The electric field is high enough to ionize some of the mercury vapor
inside the tube, which then emits UV and makes the phosphor glow.  You
don't need much field... a few hundred V/m is enough to get it going.
Considering that the field near the TC is probably around 100-200 kV/meter,
you can be pretty far away and still have the few hundred.  A program like
Etesla will show you the relative field strength as a function of distance,
and you could probably use it to figure how far you can get and still light
up the tube.

Note that the tube doesn't glow anywhere near as bright as it does when
running in a standard fixture, but, since you're usually doing the demo in
the dark, it looks mighty bright.  

Some interesting aspects... you can stand under a HV transmission line and
see a tube glow... stand off to one side and it has to be pretty dark.  If
you want to be a fearmonger, you can take a 2 or 3 second time exposure,
and the tube will look a lot brighter.

Warm tubes glow easier than cold tubes (more vaporized mercury!)

Your hand and body can act as a capacitively coupled antenna and increase
the field somewhat to get it to glow better.

Watch out when doing this that you don't get a streamer to one end of the
tube while you hold the other.  The tube is a reasonable conductor for a
direct strike, and you WILL get shocked.  (First hand personal experience
here....)


Neon signs will also light up, but in my limited experience, it takes more
field to get them to glow.... probably some geometry and gas pressure
effect...  afterall, neon signs need many kV to "strike" (hence the NST at
15 kV).. Fluorescent ballasts only kick out 500 or so volts to start a 8
foot long tube.  

Tesla list wrote:
> 
> Original poster: "Michael Rothberg by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <fishboymichael-at-telocity-dot-com>
> 
> How does the output of a tesla coil light a fluorescent tube from a
> distance without direct contact?
> 
> --
> Whatever you do will be insignificant, but it is very important that you
> do it.
>                               Mahatma Gandhi
> 
> Take care,
> Michael