How Does Glow-in-the-Dark Work?

Glow-in-the-dark powders, glow sticks, ropes, etc., are all fun examples of products using luminescence, but do you know the science behind how it works?

The Science Behind Glow-in-the-Dark

"Glow-in-the-dark" falls under several different sciences including:

• Photoluminescence by definition is the emission of light from a molecule or atom that has absorbed electromagnetic energy. Examples include fluorescence and phosphorescence materials. The glow-in-the-dark plastic constellation kits that you stick on your wall or ceiling are an example of a photoluminescence-based product.
• Bioluminescence is the light emitted by living organisms using an internal chemical reaction (think deep sea creatures).
• Chemiluminescence is the emission of light without the emission of heat as the result of a chemical reaction (e.g., glowsticks),
• Radioluminescence is created by the bombardment of ionizing radiation.

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How Glow in the Dark Stuff Works

By Anne Marie Helmenstine, Ph.D.

Chemiluminescence and photoluminescence are behind the majority of glow-in-the-dark products. According to Alfred University professors, "the distinct difference between chemical luminescence and photoluminescence is that for light to work via chemical luminescence, a chemical reaction has to occur. However, during photoluminescence, light is released without a chemical reaction.

The History of Glow-in-the-Dark

Phosphorus and its various compounds are phosphorescents or materials that glow-in-the-dark. Before knowing about phosphorus, its glowing properties were reported in ancient writings. The oldest known written observations were made in China, dating back to 1000 BCE regarding fireflies and glow-worms. In 1602, Vincenzo Casciarolo discovered the phosphorus-glowing "Bolognian Stones" just outside of Bologna, Italy. This discovery started the first scientific study of photoluminescence.

Phosphorus was first isolated in 1669 by German physician Hennig Brand. He was an alchemist who was attempting to change metals into gold when he isolated phosphorus. All photoluminescence glow-in-the-dark products contain phosphor. To make a glow-in-the-dark toy, toymakers use a phosphor that is energized by normal light and that has a very long persistence (the length of time it glows). Zinc Sulfide and Strontium Aluminate are the two most commonly used phosphors.

Glowsticks

Several patents were issued for "Chemiluminescent Signal Devices" during the early seventies that were used for naval signaling. Inventors Clarence Gilliam and Thomas Hall patented the first Chemical Lighting Device in October 1973 (Patent 3,764,796). However, it is not clear who patented the very first glowstick designed for play.

In December 1977, a patent was issued for a Chemical Light Device to inventor Richard Taylor Van Zandt (U.S. Patent 4,064,428). Zandt's design was the first to add a steel ball inside the plastic tube that when shook would break the glass ampoule and start the chemical reaction. Many toy glowsticks were built based on this design.

Modern Glow-in-the-Dark Science

Photoluminescence spectroscopy is a contactless, nondestructive method of probing the electronic structure of materials. This is from a patent-pending technology developed at Pacific Northwest National Laboratory that uses small organic molecule materials to create organic light-emitting devices (OLEDs) and other electronics.

Scientists in Taiwan say they have bred three pigs that "glow-in-the-dark".