{"id":335,"date":"2010-04-22T04:34:01","date_gmt":"2010-04-22T11:34:01","guid":{"rendered":"http:\/\/www.todayifoundout.com\/?p=335"},"modified":"2013-06-20T22:05:04","modified_gmt":"2013-06-21T05:05:04","slug":"how-glow-in-the-dark-stuff-works","status":"publish","type":"post","link":"https:\/\/www.todayifoundout.com\/index.php\/2010\/04\/how-glow-in-the-dark-stuff-works\/","title":{"rendered":"How Glow in the Dark Stuff Works"},"content":{"rendered":"

\"glow-in-the-dark\"<\/a>Today I found out<\/a> how glow in the dark stuff works.\u00a0 Glow in the dark products all contain some type of phosphor.\u00a0 Phosphors are any substance that radiates light after being energized in some way. There are literally thousands of chemicals that are phosphors.\u00a0\u00a0 These chemicals all have varying degrees of brightness, color, and length of time they glow after being energized.<\/p>\n

There are three main types of ways these phosphors end up getting energized.\u00a0 The first group, which is most common for glow in the dark items, is made up of phosphorescent items;\u00a0 the second group is made up of chemiluminescent items;\u00a0 and the third group is made up of radioluminescent items.<\/p>\n

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Phosphorescent glow in the dark items are things like the glow in the dark stars many people put on their ceilings.\u00a0 These items will absorb light radiation and will later re-emit that stored light energy over some period of time, at some level of brightness.\u00a0 So the best phosphorescent glow-in-the-dark items will be able to store quite a bit of this light and will emit it back out later relatively slowly, so it glows longer, not blowing its wad all at once.<\/p>\n

More technically speaking, with most items that absorb and re-emit light, this process happens extremely quickly at something like 10 nanoseconds to absorb and emit.\u00a0\u00a0 In this special case of phosphorescence, the absorbed light energy transitions to a higher energy state, usually to something called a “triplet state”.\u00a0 Because of this, the energy can get trapped in this triplet state and will take time to return to the lower energy state.\u00a0 In certain phosphorescent compounds the lifetime of the triplets can last minutes or even hours, allowing these compounds to effectively store light energy in the form of slowly degrading excited electron states.\u00a0 So basically, the longer the triplet lifetime, the longer it will glow, and vice-verse.<\/p>\n

Another class of glow in the dark items are the chemiluminescent variety.\u00a0 These items glow because of some chemical reaction taking place.\u00a0 Generally speaking, these will have two chemicals that interact to release energy and will also have some sort of fluorescent dye that will convert this energy (usually energy in the form of UV light) into light that is in a light spectrum humans can see; the visible spectrum.<\/p>\n

The most common chemiluminescent glow in the dark item is the glow stick.\u00a0 Inside a glow stick is a sealed glass vial containing some chemical.\u00a0 This is enclosed inside the plastic glow stick container that contains a different chemical and a fluorescent dye.\u00a0 In order to get it to glow, you crack the glass vial inside, which releases the chemical it contains; this then mixes with the chemical in the outer plastic container.\u00a0\u00a0 When the two chemicals mix, it causes a chemical reaction that produces energy that then is converted by the fluorescent dye to visible light that is not produced by heat, chemiluminescence!\u00a0 The color of the light put off\u00a0 is determined by the fluorescent dye.<\/p>\n

Even though the light is not caused by heat in chemiluminescence, heat does effect it, as anyone knows who’s put a glow stick in a freezer.\u00a0 What’s happening here is that the chemical reaction ends up slowing down as the molecules cool.\u00a0 This will make for a dimmer glow that lasts longer.\u00a0 On the flip side, you can put a glow stick in boiling water and you will see it gets brighter as the chemical reactions happen faster, but won’t glow nearly as long.<\/p>\n

*Note: chemiluminescence is seen all over the place naturally in living things like fireflies and various sea life.\u00a0 When chemiluminescence occurs naturally in biological creatures it is called Bioluminescence.\u00a0 Interestingly, the firefly has the highest known quantum efficiency (88%) for any chemiluminescent reaction.<\/p>\n

The least common group of glow in the dark items is the radioluminescent group.\u00a0 However, you will still see these from time to time.\u00a0 This class of glow in the dark items works by taking some phosphor and mixing it with a radioactive element.\u00a0 The radioactive emissions then energize the phosphor continuously for the entire life of the radioactive element.\u00a0 You’ve probably seen certain expensive watches that have hands that glow using this method.\u00a0 The three most common radioactive materials used here are radium, which has a half-life of 1600 years; tritium, which has a half-life of 12 years; and the man-made promethium which has a half-life of about 3 years.<\/p>\n

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