Glow-in-the-dark paint is used in several different industries. Glow-in-the-dark body paint can be applied safely to the skin, while artwork paint is meant to be used on canvas to give paintings glow in the dark accents, and other paints are meant to be used on metallic objects like cars. Usually, glow-in-the-dark paint works by a different, more permanent chemical process than glow sticks or glow bracelets, although the two are related.
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The key to glow-in-the-dark paint is a family of substances known as phosphors or phosphorescent materials. These substances have special qualities that allow them to produce light of their own under certain circumstances. Many of these substances are heavy metals or toxic compounds, so they cannot be used in all paint, but particles of phosphorescent materials are mixed in with paints designed to hold the particles in a substrate. Zinc sulfide, strontium aluminate, and alkaline earth silicate are some of the most common substances. Zinc sulfide is approved for use in body paint.
When phosphorescent materials come in contact with light energy, they absorb some of the energy and hold it in what is known as a "meta-stable" state. This means that light is not immediately reflected (as is the case with most substances) nor completely absorbed, but instead it stay in the atoms of the substance, making them more energetic. Eventually, the atoms release this pent-up energy in the form of photons, a delayed release that causes the substance to glow after the light is gone.
Activating and Emitting
Depending on the glow-in-the-dark paint, some types of light are activating, and some types are emitting. Activating wavelengths are those that the paint will absorb and hold, while emitting wavelengths are the type of light that the paint will produce, usually a different color than the light absorbed. Red, orange and green emitting light are the most common, while some aluminate versions also emit blue.
Chemiluminescence is a term used for short-term glow-in-the-dark products that use solutions which interact with each other to form chemical light. Instead of absorbing light from other sources, these solutions exchange energy and produce lightwaves from other sources. While these substances are not highly toxic, they are rarely used as glow-in-the dark paint, since they only last several hours before fading away. Sometimes chemiluminescent paint is used at entertainment events.
Types of Paint
Glow-in-the-dark paint comes in two different varieties, a kind marked "daytime" and a kind without the daytime label. Daytime paints are most clear and show the paint colors beneath the coating for daytime displays while glowing with their own colors in the dark. Paints without daytime features are opaque, and their colors will only be seen in low light.