Structure in Life as in Death
The following fluorescent
tubes were salvaged from a disposal bin, chosen for their diversity
Partial principles of a fluorescent lighting system
The central element
in a fluorescent lamp is a sealed glass tube. The tube contains a small
bit of mercury and an inert gas, typically argon, kept under very low
pressure. The tube also contains a phosphor powder, coated along the
inside of the glass. The tube has two electrodes, one at each end, which
are wired to an electrical circuit. The electrical circuit is hooked
up to an alternating current (AC) supply.
you turn the lamp on, the current flows through the electrical circuit to
the electrodes. There is a considerable voltage across the electrodes, so
electrons will migrate through the gas from one end of the tube to the other.
This energy changes some of the mercury in the tube from a liquid to a gas.
As electrons and charged atoms move through the tube, some of them will
collide with the gaseous mercury atoms. These collisions excite the atoms,
bumping electrons up to higher energy levels. When the electrons return
to their original energy level, they release light photons.
electrons in mercury atoms are arranged in such a way that they mostly
release light photons in the ultraviolet wavelength range. Our eyes don't
register ultraviolet photons, so this sort of light needs to be converted
into visible light to illuminate the lamp.This
is where the tube's phosphor powder coating comes in. Phosphors are substances
that give off light when they are exposed to light. In a fluorescent lamp,
the emitted light is in the visible spectrum -- the phosphor gives off
white light we can see. Manufacturers can vary the colour of the light
by using different combinations of phosphors.
you send an electrical current through a wire it generates a magnetic
field. Positioning the wire in concentric loops amplifies this field.
In short, a coiled length of wire in a circuit (an inductor) opposes change
in the current flowing through it.
The circuitry also includes a starter, but we just ran out of space
Early in the evolution
of the fluorescent tube various experiments were carried out, the more
‘practical’ of which were designed and built by Peter Cooper-Hewitt
in the early 1900’s. One such model employed a one-metre-long
tube, with an electrode of iron or graphite at one side and mercury
at the other, started by tilting the tube allowing the mercury to make
the initial contact.
Extract from ‘History
of Light and Lighting’ pg 34