Flourescents (was: What tools do you carry, always

From: Jim Arnott <jrasite_at_eoni.com>
Date: Thu Dec 7 20:05:04 2000

>From "The Illustrated Science and Invention Encyclopedia":

Fluoresent discharge tube - ...the type most often used is a slender
glass tube filled with mercury vapor at low pressure, with argon added
to help starting...

At each end of the tube is a filament-type electrode coated with a
material that easily emits electrons when heated. When the current -
usually alternating current - is switched on, the filaments heat up
and emit electrons, each one acting as the anode or cathode depending
on the half-cycle of the current. A high voltage between the
electrodes is needed to start the argon discharge, and this is done
using a starter or a choke or ballast. The starter automatically
breaks the circuit when the filaments have heated up, causing the
choke, which is an induction coil, to produce a brief pulse of high
voltage electricity. This starts the argon discharge and, very
shortly, a mercury discharge. This is self sustaining, with a
continuous flow of electrons between the electrodes.

The radiation from the ionized vapour is strong in the ultraviolet.
This falls on a coating of fluorescent material on the inside of the
tube, which glows by absorbing the invisible and harmful ultraviolet
and re-radiating it as vivible light. The color of this light can be
chosen by suitably arranging the mix of fluorescent coating, the most
common shades being 'white' and 'warm white'.
Received on Thu Dec 07 2000 - 20:05:04 GMT