How Light Sticks Work
Since their invention 25 years ago, light sticks have become a Halloween
staple. They're perfect as safety lights because they're portable, cheap and they
emit a ghostly glow. Light sticks are also extremely popular on the rave scene
(as are light necklaces, light glasses and light rope), and they make an ideal
lamp for SCUBA divers and campers.
While it may seem like supernatural magic, the technology behind light sticks
is actually very simple. In this article, we'll look inside a light stick to find out
how it gives off such a strong light with no bulb and no battery.
The Glow
Light is a form of energy, which can be emitted through a variety of processes.
These processes include:
 Incandescence - The emission of light due to heat (as in an ordinary light
bulb or a gas lantern)
 Fluorescence and phosphorescence - The emission of light in response to
radiation energy (as in a fluorescent light bulb or a television)
 Laser generation - The concentrated emission of light using stimulated emission
Light sticks are a "cool light" source -- unlike a conventional light bulb, they do not heat up while they glow.
All these processes work on the same basic principle: An outside source of energy excites atoms, causing them to
release particles of light called photons. When you burn something, for example, heat energy causes the atoms that
make up the material to speed up. When the atoms speed up, they collide with each other with greater force. If the
atoms are excited enough, the collisions will transfer energy to some of the atom's electrons. When this happens, an
electron will be temporarily boosted to a higher energy level (farther away from the atom's nucleus). When it
eventually falls back down to its original level (closer to the nucleus), it releases some of its energy in the form of
light photons.
A light stick does the same basic thing, but it uses a chemical reaction to excite the atoms in a material.
The Chemical Reaction
In the last section, we saw that light sticks use energy
from a chemical reaction to emit light. This chemical
reaction is set off by mixing multiple chemical
compounds.
Light sticks come in a variety of colours. The colour
of the light is determined by the chemical make-up
of the fluorescent dye in the stick.
The reaction between the different compounds in a
light stick causes a substantial release of energy. Just
as in an incandescent light bulb, atoms in the
materials are excited, causing electrons to rise to a
higher energy level and then return to their normal
levels. When the electrons return to their normal levels, they release energy as light. This process is called
chemiluminescence.
The chemical reaction in a light stick usually involves several different steps. A typical commercial light stick
holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here's
the sequence of events when the two solutions are combined:
1. The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an
unstable peroxyacid ester.
2. The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound.
3. The cyclic peroxy compound decomposes to carbon dioxide.
4. This decomposition releases energy to the dye.
5. The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy as light.
The light stick itself is just a housing for the two solutions involved in the reaction -- essentially, it is portable
chemistry experiment. In the next section, we'll see how bending the light stick sets this experiment in motion.
The Activator
Before you activate the light stick, the two solutions are kept in separate chambers. The phenyl oxalate ester and
dye solution fills most of the plastic stick itself. The hydrogen peroxide solution, called the activator, is contained
in a small, fragile glass vial in the middle of the stick.
A light stick consists of a glass vial,
containing one chemical solution, housed
inside a larger plastic vial, containing another
solution. When you bend the plastic vial, the
glass vial breaks, the two solutions flow
together, and the resulting chemical reaction
causes a fluorescent dye to emit light.
When you bend the plastic stick, the glass
vial snaps open, and the two solutions flow
together. The chemicals immediately react to
one another, and the atoms begin emitting
light. The particular dye used in the chemical
solution gives the light a distinctive colour.
Depending on which compounds are used, the
chemical reaction may go on for a few
minutes or for many hours. If you heat the
solutions, the extra energy will accelerate the
reaction, and the stick will glow brighter, but
for a shorter amount of time. If you cool the
light stick, the reaction will slow down, and
the light will dim. If you want to preserve
your light stick for the next day, put it in the
freezer -- it won't stop the process, but it will
drag out the reaction considerably.
Heating a light stick will accelerate the chemical
reaction, causing the dye to emit a brighter glow. The
light stick on the left has been activated and kept at
room temperature. The light stick on the right has been
activated and placed in scalding hot water for one
minute.
Light sticks are just one application of an important
natural phenomenon -- luminescence. Generally
speaking, luminescence is any emission of light that is
not caused by heating. Among other things,
luminescence is used in televisions, neon lights and
glow-in-the-dark stickers. It's also the principle that
lights up a firefly and makes some rocks glow after
dark.
**************************************Ref: How Stuff Works