What Is the Difference Between Black Light & Ultra Violet Light?
To explain the way light travels and functions, scientists describe it as a wave. They measure a light wave's length between its rolling tips, called crests. This measurement is called a wavelength, calculated in tiny units called nanometers. Different types of light have different wavelengths. The human eye is only capable of seeing some of these. Black light and ultra violet light are not a part of the spectrum visible to the naked eye; but that doesn't mean they can't be measured and identified.
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Definition: Ultra Violet Light
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Ultra violet (UV) light is a type of light emitted by the sun. Because of its short wavelength, it's not visible to human eyes although you've probably experienced its effects---ultra violet light is the kind of light responsible for sunburns. Not all UV light reaches the surface of the earth; the ozone layer blocks many of these rays, shielding you from their harmful effects.
Types of Ultra Violet Light
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There are three different kinds of ultra violet light: near, far and extreme. They are distinguished both by their wavelengths and the amount of radiation they possess. Near ultra violet, also called UVA, is the least radioactive and closest to the type of light we can see. Far ultra violet, also called UVB, is more radioactive; it's also the type of ultra violet light scientists know the least about. Finally, extreme ultra violet, also called UVC, is the most radioactive of the three, similar to X-rays.
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Specific Wavelengths of Ultra Violet Light
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Near (UVA) ultra violet light has a wavelength of 300 to 400 nm. Far (UVB) ultra violet light has a wavelength of 280 to 315 nm. Extreme (UVC) ultra violet light has a wavelength of 200 to 280 nm.
Definition: Black Light
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Black light is one type of UV light. It falls into the UVA group, the type of UV light with the longest wavelength. Black light has a wavelength that measures anywhere from 320 to 400 nanometers. Most commercial black lights are 380 to 390 nm, just out of the range of light that's visible to the human eye. So while it's true that all black light is UV light, not all UV light is black light.
Uses for Black Light
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Black light has a number of fun and interesting uses. Many objects fluoresce, or glow, when illuminated by black light. You can buy pens with ink that's only visible under the glow of a black light--useful for marking possessions in case they're stolen and later recovered. You may have had your hand stamped by a dance club with a type of ink that only glows under black light. The urine of rats and mice glows under black light, so you may see exterminators using them to find pests. Similarly, household stains often show up under black like so investigators can use them to find traces of semen or saliva.
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