Objects can glow in the dark through phosphorescence, chemiluminescence, or radioluminescence. Phosphors are the most common, using chemicals that store energy when exposed to light. Bioluminescence is also possible in living organisms.
Glow in the dark, also called luminescence, is usually a simple matter of chemistry. Some chemicals store energy when exposed to light, then slowly release that energy, which causes them to emit a small amount of light and then glow. Other chemicals will react with each other, causing their electrons to be excited, and they will light up as those electrons release energy. Radioactive elements can also be used to make things glow. These three ways things glow in the dark are known as phosphorescence, chemiluminescence, and radioluminescence.
Examples
An object is said to glow in the dark when it emits light without being connected to a source of energy, such as an electric current or battery, and without emitting more than a small amount of heat. A lit match, a light bulb, or a cell phone screen, for example, might emit light in the dark, but it would not appear to glow in the dark. The hands of a mechanical clock, toys, paint, and novelty items are examples of things that sometimes glow in the dark.
Phosphorescence
The most common way to make an object glow in the dark is to use chemicals called phosphors to produce light. Objects coated with these chemicals must be exposed to light before they can glow in the dark. The light energizes the phosphors and excites their electrons. As the electrons slowly lose this extra energy, the release of the energy creates a light that is usually a little dim.
Scientists have created many phosphors in the laboratory, but zinc sulfide and strontium aluminate are the most commonly used in fluorescent products. Strontium Aluminate is a newer technology and its glow lasts longer. The chemicals are often mixed with plastic that is molded into a glow-in-the-dark object or added to other material to make things like glow-in-the-dark paint or makeup.
chemiluminescenza
Another way to make objects glow in the dark is through a chemical reaction. Two chemicals are mixed together, and the resulting reaction causes the electrons to be excited and moved to a higher energy level. When the electrons return to normal levels, they release energy, producing a glow. This is the type of reaction that is used to create the light in glow sticks.
Radioluminescenza
Some objects will glow without needing to be exposed to light or “charged”. These items still use phosphors to create the glow, but add a radioactive element such as radium to the compound. The radioactive element emits small amounts of radiation – not enough to be dangerous – which constantly charge the phosphors in the same way as a light. Radiation-charged phosphors are typically used on clocks or hands that need to glow for hours after a light has been turned off, such as in case the owner needs to check the time in the middle of the night.
Bioluminescenza
Many living organisms are able to glow in the dark due to chemical reactions. Some contain all the chemicals they need to glow, while others glow by reaction to an element in its environment, such as oxygen. Fireflies, fireflies, creatures that live in the depths of the ocean, and some types of fungi are among the animals and plants that can glow. In some cases, such as with deep sea creatures, bioluminescence is its only light source. Other animals and plants shine for protection, camouflage, to attract mates, or for other reasons.
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