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The Visible Spectrum
Wavelengths and Colors
by Anne Marie
Helmenstine, Ph.D.
The human eye sees color over wavelengths ranging roughly
from 400 nanometers (violet) to 700 nanometers (red).
Light from 400–700 nanometers (nm) is called visible light,
or the visible spectrum, because humans can see it.
Light outside this range may be visible to other organisms
but cannot be perceived by the human eye.
Colors of light that correspond to narrow wavelength bands
(monochromatic light) are the pure spectral colors learned using the ROYGBIV
acronym: red, orange, yellow, green, blue, indigo, and violet.
Wavelengths of Visible Light
Some
people can see further into the ultraviolet and infrared ranges than others, so
the "visible light" edges of red and violet are not well-defined.
Also,
seeing well into one end of the spectrum doesn't necessarily mean you can see
well into the other end of the spectrum.
You
can test yourself using a prism and a sheet of paper.
Shine
a bright white light through the prism to produce a rainbow on the paper. Mark
the edges and compare the size of your rainbow with that of others.
The
wavelengths of visible light are:
Violet:
380–450 nm (688–789 THz frequency)
Blue:
450–495 nm
Green:
495–570 nm
Yellow:
570–590 nm
Orange:
590–620 nm
Red:
620–750 nm (400–484 THz frequency)
Violet
light has the shortest wavelength, which means it has the highest frequency and
energy.
Red
has the longest wavelength, the shortest frequency, and the lowest energy.
The
Special Case of Indigo
There
is no wavelength assigned to indigo. If you want a number, it's around 445
nanometers, but it doesn't appear on most spectra.
There's
a reason for this. English mathematician Isaac Newton (1643–1727) coined the
word spectrum (Latin for "appearance") in his 1671 book
"Opticks."
He
divided the spectrum into seven sections — red, orange, yellow, green, blue,
indigo, and violet — in keeping with the Greek sophists, to connect the colors
to days of the week, musical notes, and the known objects of the solar system.
So,
the spectrum was first described with seven colors, but most people, even if
they see color well, can't actually distinguish indigo from blue or violet.
The
modern spectrum typically omits indigo. In fact, there is evidence Newton's
division of the spectrum doesn't even correspond to the colors we define by
wavelengths.
For
example, Newton's indigo is the modern blue, while his blue corresponds to the
color we refer to as cyan. Is your blue the same as my blue? Probably, but it
may not be the same as Newton's.
Colors
People See That Aren't on the Spectrum
The
visible spectrum does not encompass all the colors humans perceive because the
brain also perceives unsaturated colors (e.g., pink is an unsaturated form of
red) and colors that are a mixture of wavelengths (e.g., magenta).
Mixing
colors on a palette produces tints and hues not seen as spectral colors.
Colors
Only Animals Can See
Just
because humans can't see beyond the visible spectrum doesn't mean animals are
similarly restricted.
Bees
and other insects can see ultraviolet light, which is commonly reflected by
flowers. Birds can see into the ultraviolet range (300–400 nm) and have plumage
visible in UV.
Humans
see further into the red range than most animals. Bees can see color up to
about 590 nm, which is just before orange starts. Birds can see red, but not as
far toward the infrared range as humans.
Some
people believe the goldfish is the only animal that can see both infrared and
ultraviolet light, but this notion is incorrect. Goldfish cannot see infrared
light.
Anne
Marie Helmenstine, Ph.D.
Introduction
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.
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,
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Publisher of the Year by Digiday, a leading industry publication.
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