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INTRODUCTION
Have you ever seen a lightning flash and wonder
how the light was produced? This strobe light kit not
only explains how a high voltage discharge
produces light, but reproduces those bolts of
lightning in a small glass tube. Even more amazing
is the fact you will be able to control the moment
each flash occurs with a trigger circuit. Strobe lights
THEORY OF OPERATION
WHAT IS A GAS?
All matter is composed of atoms arranged in
patterns called molecules.
molecules are held in place and cannot move about
easily. In a liquid, the molecules move freely, but are
still loosely bound to each other. In a gas, the
molecules are separated by great distances and
bounce about like ping-pong balls in a large box.
The molecules of a gas are not bound to each other
and will dissipate into the surrounding space if
released from their container. These different states
of matter are shown in Figure 1.
Figure 1
Solid
The glass tube in your strobe light kit is filled with a
rare gas called Xenon. This gas is used because it
is easy to ionize.
WHAT IS AN ION?
Gas atoms have no electronic charge on them in
their normal state. There are just as many positively
charged protons as there are negatively charged
electrons. Therefore, the net charge on the atom is
zero. If, however, a negatively charged electron is
removed from one of the atoms, the atom is left with
a positive charge and it is called a positive ion. This
creation of ions is shown in Figure 2.
Figure 2
Protons
Electrons
Normal Gas
Positive Ion
Molecule
In a solid, these
Liquid
Gas
Negative Ion
are used to stop motion by adjusting the trigger rate
to the speed of a moving object. They are also used
to produce light for photography at the moment the
camera shutter is opened. In the text that follows,
mechanical analogies are used to help explain
certain processes that are otherwise difficult to
visualize.
The amount of energy it takes to create an ion is
measured in electron volts.
energy needed to produce ions for different gases.
As you can see, Xenon requires much less energy
than Neon to produce ions. If the glass tube in your
kit contained Neon, the amount of energy needed to
ionize the gas would be 1.87 times greater. This
would shorten the life of the batteries by using
almost twice the energy for each flash. It is a law of
nature that opposite charges attract each other and
similar charges repel. When a gas molecule is
turned into a positive ion, it is attracted to a negative
charge. The positive gas ion is placed in a strong
electric field, it will rapidly accelerate toward the
negative plate. As it moves, it will strike other gas
molecules, knocking electrons free and creating
more positive ions. These newly created ions will be
attracted by the negative plate, accelerate and
create even more positive ions (see Figure 3). The
avalanche process will continue until all of the gas in
the tube is ionized allowing a large current to flow
through the tube and collapse the electric field. As
the electrons are knocked about during the
ionization process,
they release small
packets of energy
called photons that
radiate from the
tube. The human
eye perceives this
burst of photons as
a brilliant flash of
light.
-3-
Table 1 shows the
Gas
Ionization
Energy
Helium
24.5
Neon
21.5
Nitrogen
16.7
Hydrogen
15.9
Argon
15.7
Carbon Monoxide
14.2
Oxygen
13.5
Krypton
13.3
Water Vapor
13.2
Xenon
11.5
Mercury
10.4
Table 1
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