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What Materials Glow Under a Black or Ultraviolet Light?

UV Active Materials

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These Lego Bionicle pieces glow under a black light.

These Lego Bionicle pieces glow under a black light. Many Lego parts glow, pretty much in all the colors of the rainbow.

Eric Helmenstine
UV-lamps also emit some visible violet light.

Ultraviolet light is invisible, but black lights or UV-lamps also emit some visible violet light.

Kallemax, wikipedia.org
The ice cubes in this drink glow in the dark.

The ice cubes in this drink glow in the dark. Do you know how I did it?

Anne Helmenstine

Question: What Materials Glow Under a Black or Ultraviolet Light?

Answer: There are a lot of everyday materials that fluoresce, or glow, when placed under a black light. A black light gives off highly energetic ultraviolet light. You can't see this part of the spectrum, which is how 'black lights' got their name. Fluorescent substances absorb the ultraviolet light and then re-emit it almost instantaneously. Some energy gets lost in the process, so the emitted light has a longer wavelength than the absorbed radiation, which makes this light visible and causes the material to appear to glow.

Fluorescent molecules tend to have rigid structures and delocalized electrons. Examples of common materials that contain fluorescent molecules include:

  • White Paper
    White paper is treated with fluorescent compounds to help it appear brighter and therefore whiter. Sometimes forgery of historical documents can be detected by placing them under a black light to see whether or not they fluoresce. White paper made post-1950 contains fluorescent chemicals while older paper doesn't.
  • People
    Humans have stripes, called Blaschko's Lines, that may be observed under a black or ultraviolet light. They don't glow so much as become visible.
  • Petroleum Jelly
    Petroleum jelly, such as Vaseline, glows a bright blue color under a fluorescent light.
  • US $20 Bill
    Modern US $20 bills contain a security strip near one edge that glows bright green under a black light.
  • Tonic Water
    The bitter flavoring of tonic water is due to the presence of quinine, which glows blue-white when placed under a black light.
  • Body Fluids
    Many body fluids contain fluorescent molecules. Forensic scientists use ultraviolet lights at crime scenes to find blood, urine, or semen (all fluorescent).
  • Vitamins
    Vitamin A and the B vitamins thiamine, niacin, and riboflavin are strongly fluorescent. Try crushing a vitamin B-12 tablet and dissolving it in vinegar. The solution will glow bright yellow under under a black light.
  • Chlorophyll
    Chlorophyll makes plants green, but it fluoresces a blood red color. Grind some spinach or swiss chard in a small amount of alcohol (e.g., vodka or everclear) and pour it through a coffee filter to get chlorophyll extract (you keep the part that stays on the filter, not the liquid). You can see the red glow using a black light or even a strong fluorescent bulb, such as an overhead projector lamp, which (you guessed it) gives off ultraviolet light.
  • Antifreeze
    Manufacturers purposely include fluorescent additives in antifreeze fluid so that black lights can be used to find antifreeze splashes to help investigators reconstruct automobile accident scenes.
  • Laundry Detergents
    Some of the whiteners in detergent work by making your clothing a bit fluorescent. Even though clothing is rinsed after washing, residues on white clothing cause it to glow bluish-white under a black light. Blueing agents and softening agents often contain fluorescent dyes, too. The presence of these molecules sometimes causes white clothing to appear blue in photographs.
  • Other Cleaners
    Examples of other types of cleaners that glow under black light include Irish Spring™ soap and Mr. Clean™.
  • Emperor Scorpion
    The emperor scorpion normally is dark brown or black, but it glows a bright blue-green when exposed to black light.
  • Tooth Whiteners
    Whiteners and some enamels contain compounds that glow blue to keep teeth from appearing yellow.
  • Postage Stamps
    Stamps are printed with inks that contain fluorescent dyes. However, the US stamps that I checked (printed 2008) did not glow.
  • Jellyfish
    If you have a jellyfish handy, see what it looks like under a black light in a darkened room. Some of the proteins within a jellyfish are intensely fluorescent.
  • Some Minerals and Gems
    Fluorescent rocks include fluorite, calcite, gypsum, ruby, talc, opal, agate, quartz, and amber. Minerals and gemstones are most commonly made fluorescent or phosphorescent due to the presence of impurities. The Hope Diamond, which is blue, phosphoresces red for several seconds after exposure to shortwave ultraviolet light.
  • Banana Spots
    Who knew? Shine a black light on a ripe banana with spots. Check out the area around the spots.

You may wish to browse the Black Light Photo Gallery to see more examples of materials that glow under a black light.

 

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