# What is black light?
**URL:** https://boards.straightdope.com/t/what-is-black-light/191348
**Category:** Factual Questions
**Created:** [July 28, 2003, 1:05am UTC](https://boards.straightdope.com/t/what-is-black-light/191348 "2003-07-28T01:05:28Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Susma\_Rio\_Sep](https://boards.straightdope.com/u/Susma_Rio_Sep)
#### Post date: [July 28, 2003, 1:05am UTC](https://boards.straightdope.com/t/what-is-black-light/191348/1 "2003-07-28T01:05:28Z")
Racer here tells us that a hand held black light can be used to detect the fluorescents in power steering pump fluid, so as to locate the leak in the pump.
Anyone with any idea of what a black light is? I am just an ignoramus here.
Racer has not replied further in the thread on leaks in power steering pump.
Tnanks and God bless.
Susma Rio Sep
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [July 28, 2003, 1:21am UTC](https://boards.straightdope.com/t/what-is-black-light/191348/2 "2003-07-28T01:21:31Z")
Black light is merely a popularized term for ultraviolet. Many substances fluoresce (emit light) when exposed to UV light.
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### Author:  [@JohnJet](https://boards.straightdope.com/u/JohnJet)
#### Post date: [July 28, 2003, 1:26am UTC](https://boards.straightdope.com/t/what-is-black-light/191348/3 "2003-07-28T01:26:44Z")
My non-scientific response: A black light is a light that makes certain things “glow” when they’re exposed to it. Have you ever been cosmic bowling? They use black lights there to make the pins and balls(and things like socks) glow. I’m sure someone else will come along here in a bit to tell you a more detailed description of what it is and where you can get one.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [July 28, 2003, 1:31am UTC](https://boards.straightdope.com/t/what-is-black-light/191348/4 "2003-07-28T01:31:13Z")
[How do Black-Lights work?](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=98063&highlight=ultraviolet)
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### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [July 28, 2003, 1:34am UTC](https://boards.straightdope.com/t/what-is-black-light/191348/5 "2003-07-28T01:34:40Z")
**Q.E.D.** has it. “black light” is ultraviolet light which is light having wavelengths shorter than about 400 nm but onger than, say, 100 nm. The UV lamps you buy at Spencers and other such places for your BlackLight posters is long wavelength UV (typically 300-400 nm), which is pretty safe. Shorter wavelength UV can damage eyes, kill germs, and promote skin cancer. Fortunately, its also harder to generate, since most glasses and plastics block it. You need a quartz bulb or something else special for it.