Compounds are substances made up of atoms of different elements, bonded together in rigid structure. When you combine two or more compounds, the various atoms may rearrange themselves to form new compounds. Depending on the nature of the compounds, this reaction will cause either a release of energy or an absorption of energy.

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 chemiluminesence.

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 in the form of 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.

In the last section, we saw that a light stick is a housing for two chemical solutions, which give off light when they are combined. 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 color.

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.

Blue	9,10-diphenylanthracene
Green	9,10-bis(phenylethynyl)anthracene
Yellow	1-chloro-9,10-bis(phenylethynyl)anthracene Rubrene
Orange	5,12-bis(phenylethynyl)-naphthacene Rhodamine 6G
Red	Rhodamine B

Although red fluorophors such as Rhodamine B are available, red-emitting light sticks tend not to use them in the oxalate reaction. The red fluorophors are not very stable when stored with the other chemicals in the light sticks. Instead, a fluorescent red pigment is molded into the plastic tube that encases the light stick chemicals. The red-emitting pigment absorbs the light from the high yield (bright) yellow reaction and re-emits it as red. This results in a red light stick that is approximately twice as bright as it would have been had the light stick used the red fluorophor in the solution.