ULTRAVIOLET LIGHT - Ultraviolet radiation is electromagnetic radiation or light having a wavelength greater than 100 nm but less than 400 nm. It is also known as UV radiation, ultraviolet light, or simply UV. About 10 percent of the light output of the Sun is UV radiation. When sunlight enters the Earth's atmosphere, the light is about 50% infrared radiation, 40% visible light, and 10% ultraviolet radiation. However, the atmosphere blocks about 77% of solar UV light, mostly in shorter wavelengths. Light reaching the Earth's surface is about 53% infrared, 44% visible, and 3% UV. Ultraviolet light is produced by black lights, mercury-vapor lamps, and tanning lamps. Any sufficiently hot body emits ultraviolet light (black-body radiation). Thus, stars hotter than the Sun emit more UV light.

............................................

Ultraviolet Light

Ultraviolet Radiation Definition

Chemistry Glossary Definition of Ultraviolet Radiation

by Anne Marie Helmenstine, Ph.D.

Ultraviolet radiation is another name for ultraviolet light. It is a part of the spectrum outside the visible range, just beyond the visible violet portion.

Ultraviolet Radiation Definition

Ultraviolet radiation is electromagnetic radiation or light having a wavelength greater than 100 nm but less than 400 nm.

It is also known as UV radiation, ultraviolet light, or simply UV.

Ultraviolet radiation has a wavelength longer than that of x-rays but shorter than that of visible light.

Although ultraviolet light is energetic enough to break some chemical bonds, it is not (usually) considered a form of ionizing radiation.

The energy absorbed by molecules can provide the activation energy to start chemical reactions and may cause some materials to flouresce or phosphoresce.

The word "ultraviolet" means "beyond violet". Ultraviolet radiation was discovered by the German physicist Johann Wilhelm Ritter in 1801.

Ritter noticed invisible light beyond the violet portion of the visible spectrum darkened silver chloride treated paper more quickly than violet light.

He called the invisible light "oxidizing rays," referring to the chemical activity of the radiation.

Most people used the phrase "chemical rays" until the end of the 19th century, when "heat rays" became known as infrared radiation and "chemical rays" became ultraviolet radiation.

Sources of Ultraviolet Radiation

About 10 percent of the light output of the Sun is UV radiation.

When sunlight enters the Earth's atmosphere, the light is about 50% infrared radiation, 40% visible light, and 10% ultraviolet radiation. However, the atmosphere blocks about 77% of solar UV light, mostly in shorter wavelengths. Light reaching the Earth's surface is about 53% infrared, 44% visible, and 3% UV.

Ultraviolet light is produced by black lights, mercury-vapor lamps, and tanning lamps.

Any sufficiently hot body emits ultraviolet light (black-body radiation). Thus, stars hotter than the Sun emit more UV light.

Categories of Ultraviolet Light

Ultraviolet light is broken into several ranges, as described by ISO standard ISO-21348:

Name	Abbreviation	Wavelength (nm)	Photon Energy (eV)	Other Names
Ultraviolet A	UVA	315-400	3.10–3.94	long-wave, black light (not absorbed by ozone)
Ultraviolet B	UVB	280-315	3.94–4.43	medium-wave (mostly absorbed by ozone)
Ultraviolet C	UVC	100-280	4.43–12.4	short-wave (completely absorbed by ozone)
Near ultraviolet	NUV	300-400	3.10–4.13	visible to fish, insects, birds, some mammals
Middle ultraviolet	MUV	200-300	4.13–6.20
Far ultraviolet	FUV	122-200	6.20–12.4
Hydrogen Lyman-alpha	H Lyman-α	121-122	10.16–10.25	spectral line of hydrogen at 121.6 nm; ionizing at shorter wavelengths
Vacuum ultraviolet	VUV	10-200	6.20–124	absorbed by oxygen, yet 150-200 nm can travel through nitrogen
Extreme ultraviolet	EUV	10-121	10.25–124	actually is ionizing radiation, although absorbed by the atmosphere

Seeing UV Light

Most people cannot see ultraviolet light, however, this is not necessarily because the human retina can't detect it.

The lens of the eye filters UVB and higher frequencies, plus most people lack the color receptor to see the light.

Children and young adults are more likely to perceive UV than older adults, but people missing a lens (aphakia) or who have had a lens replaced (as for cataract surgery) may see some UV wavelengths.

People who can see UV report it as a blue-white or violet-white color.

Insects, birds, and some mammals see near-UV light. Birds have true UV vision, as they have a fourth color receptor to perceive it.

Reindeer are an example of a mammal that sees UV light. They use it to see polar bears against snow. Other mammals use ultraviolet to see urine trails to track prey.

Anne Marie Helmenstine, Ph.D.

·   Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

·   Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

·   ThoughtCo and About Education chemistry expert since 2001.

·   Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

Anne Marie Helmenstine, Ph.D.

​ThoughtCo and Dotdash

ThoughtCo is a premier reference site focusing on expert-created education content. We are one of the top-10 information sites in the world as rated by comScore, a leading Internet measurement company. Every month, more than 13 million readers seek answers to their questions on ThoughtCo.

For more than 20 years, Dotdash brands have been helping people find answers, solve problems, and get inspired. We are one of the top-20 largest content publishers on the Internet according to comScore, and reach more than 30% of the U.S. population monthly. Our brands collectively have won more than 20 industry awards in the last year alone, and recently Dotdash was named Publisher of the Year by Digiday, a leading industry publication.

https://www.thoughtco.com/definition-of-ultraviolet-radiation-604675