If you’ve ever been out trick or treating with your child on Halloween you’ve likely encountered a marvel of chemistry and science without having even realized it. A small, 6” plastic tube that seems to miraculously glow on its own, otherwise known as a light stick or glow stick.

These simple devices that many of us have fond memories of using as a child are still just as popular today as in past years, having seen a resurgence of use at nearly all night time events from birthday parties to weddings and nearly any event in between.But what you might not realize is all the complexity that goes into making a small plastic tube magically light up without the aid of batteries or any external power sources. And it is here, within the realm of chemistry and human ingenuity, that the secret behind just how glow sticks glow is answered.

Before delving into the fascinating science behind the glow stick, what you might not realize is just how varied in sizes and uses glow sticks have become. Typically when people think of glow sticks what comes to mind is the basic small stick, about 6 inches long and often glowing green. But with modern glow stick design this is only the tip of the iceberg with glow sticks now coming in all sorts of shapes, sizes, and colors. One can now purchase glow bracelets than wrap around your wrist, glow necklaces for adding that extra touch to a Halloween costume, glow stir sticks for using in drinks at parties, and even long lengths of glow rope. The colors are just as varied, with options such as blue, red, yellow, purple, and pink to name just a few. It’s not uncommon to even see glow products that are a combination of different colors. But this leads to the question of how exactly do glow sticks get their distinctive

Chemical glow sticks as their name implies operate off of a rather simple chemical reaction. A chemical reaction is essentially a process that begins with two or more different solutions that come into contact with one another, which then begins a process that results in some sort of chemical change in the reactants. Most importantly to chemical glow products is the fact that this process also often causes energy to be released. For example, when a log is burning a chemical reaction is actually taking place that is changing the composition of that log, as well as resulting in the release of energy in the form of heat and light. As you might already be guessing in the case of glow sticks light is the form of energy released from the chemical reaction (though unlike fire, no heat is produced). But what are these chemicals that are able to produce such varied colors and intensities of light?

There are three liquids needed for the chemical reaction within glow sticks. The first liquid needed is something known as fluorescent dye. This is the chemical that determines what color of light will be emitted by the glow stick once the chemical reaction is allowed to occur. Surprisingly enough the color of this dye does not always match the color the glow stick will glow. Some people are quite shocked when they activate a clear glow stick only for it to light up blue!

The next solution needed is something most people are actually quite familiar with, hydrogen peroxide. This is a rather common chemical that you might even have in your medicine cabinet to use as a disinfectant for cuts. Finally the last ingredient needed is a chemical called phenyl oxalate ester. Once all these solutions are combined and mixed together a series of chemical reactions occur which ultimately leads to the fluorescent dye releasing energy in the form of light, which depending on its wavelength determines the color you see. But this then leads to the question of what prevents the chemical reaction from occurring before the glow stick is activated?

To answer this question we must look at the glow products container, which might appear deceptively simple. If you’ve ever held a glow stick you have no doubt recognized that it feels like no more than a simple plastic stick. But you also likely noted that glow sticks do not glow until they are activated, and that once they are activated they will only glow for a certain amount of time. The reason behind this is that the prior mentioned chemical reaction will only produce light for as long as the chemical compounds needed for the reaction are still present. Given enough time the chemical reaction will exhaust itself by changing all the reactants, causing the glow stick to cease glowing. So in the development of the glow stick one of the primary issues was how to keep the chemical reaction from beginning before one wanted to use the glow stick. There are essentially two ways of achieving this in a glow stick, either keeping the chemicals from mixing with one another, or bringing the chemical process down to such a slow reaction that there would still be the needed chemical components once one wanted to use the glow stick.

There are however problems with both of these approaches. The issue with slowing down the chemical reaction is simply one of time and conditions. Namely to slow down the chemical reaction within a glow stick one needs to keep it at very cold temperatures (this is why people will sometimes freeze a glow stick after it has been activated and used for a time, allowing them to use it again on the next night). This of course presents logistic problems in that who wants to purchase a glow stick that must be refrigerated at all times prior to use? Secondly, it also doesn’t entirely solve the problem since the chemical reaction will still be going on very slowly, so if one didn’t use the glow stick promptly by returning it to a warm temperature then the glow stick would run out of glow before being used for its intended purpose.

So the second and most effective option ended up being used in glow sticks, namely keeping the chemicals separate from one another until the glow stick is ready to be used. To achieve this objective all glow products are designed with two compartments. First, there is the main inner compartment which contains the fluorescent dye and the phenyl oxalate ester. Floating within this solution there is a second small vial, typically made out of glass or some other relatively fragile material, containing the hydrogen peroxide. With this design neither of the two solutions needed for the chemical reaction are able to come into contact with one another, and so no chemical reaction occurs and the solutions stay fresh and ready for use. But, if these two solutions are separate how exactly then does one activate the glow stick?

The answer to this lies in the two materials used for the glow stick, the somewhat flexible plastic outer shell, and the brittle and comparatively fragile inner glass vial. When the glow stick is ready to be used a person will grab each end of the glow stick and flex it. As the flexible outer plastic shell of the glow stick begins to bend it comes into contact with the inner glass vial, beginning to apply pressure to it. Because the glass vial is less flexible than the plastic it will break open at a much earlier point than the outer plastic, which has the end result of the glass vial breaking and spilling its contents into the larger housed area of the glow stick. It is this breaking of the glass vial that gives glow sticks their distinctive snapping noise when being activating. With the glass vial broken and its contents able to mingle and react with the liquids in the main compartment, the chemical reaction will begin and the glow stick will light up. This simple two part container design combined with the wonders of the chemicals within it is all there is to the secrets behind the glow stick we enjoy so much today.