How Glow in the Dark Toys Work

Glow in the dark toys are a fun way to make night time more magical and engage children’s imagination. However, they are not without their hazards. Most glow in the dark objects, from the plastic stars to hang on your ceiling to glow sticks used by trick-or-treaters and festivals, rely on a chemical process known as chemiluminescence. This means that in order to work they need to be exposed to light and then “recharged” by being placed in near darkness. This can be a dangerous process if chemicals are not used correctly.

Many of us have seen glow in the dark items and thought, wow, this is cool! But have you ever wondered how they really work? This Instructable will demonstrate how to perform an experiment to learn more about what makes a glow in the dark object glow. It will be based on the simple but useful technique of measuring the resistance of a resistor (using a multimeter) against time to determine how much a glow in the dark item has been charged by exposure to a light source.

Most of the stuff that glows in the dark is made of a special type of material called phosphor. Phosphors are naturally occurring materials that emit visible light when they absorb electromagnetic energy in the form of photons. When a glowing object is turned off, it slowly releases the energy stored in its phosphors and emits a faint greenish light, which we call luminescence.

During the manufacturing process of glow in the dark toys, phosphors are mixed with plastic and molded into the desired shape of the toy. Zinc sulfide is the most commonly used phosphor for making glow in the dark toys, and it naturally emits greenish light. More recently, a newer phosphor called strontium illuminate has been added to the mix as it produces a brighter glow for longer.

Some glow in the dark toys also use radioactive materials that emit visible light when exposed to radiation. These are typically more expensive but have a longer persistence of glow. Radium was once very popular for this purpose, but nowadays tritium is often used instead.

Although most modern glow in the dark products are non-toxic, it is important to read the labels and follow the directions of any glow products your child might want to use. While most of the toys available today have government standards that regulate their production, it is always wise to practice caution.

While a glow in the dark object can be recharged by being exposed to sunlight, it is possible that the chemical mixture that makes them glow may degrade over time with frequent exposure to UV rays. For this reason, it is best to store any glow in the dark objects in a protective case or container. However, if your children want to play with glow in the dark items outside and they get dirty, you can simply wash them in hot water to renew their luminescent properties.