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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.
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
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