Visible Light

Illustration of a visible wave on the electromagnetic spectrum

What is the visible light spectrum?

The visible light spectrum is the segment of the electromagnetic spectrum that the human eye can view. More simply, this range of wavelengths is called visible light. Typically, the human eye can detect wavelengths from 380 to 700 nanometers.

WAVELENGTHS OF VISIBLE LIGHT

All electromagnetic radiation is light, but we can only see a small portion of this radiation—the portion we call visible light. Cone-shaped cells in our eyes act as receivers tuned to the wavelengths in this narrow band of the spectrum. Other portions of the spectrum have wavelengths too large or too small and energetic for the biological limitations of our perception.

As the full spectrum of visible light travels through a prism, the wavelengths separate into the colors of the rainbow because each color is a different wavelength. Violet has the shortest wavelength, at around 380 nanometers, and red has the longest wavelength, at around 700 nanometers.

Left: A 3D illustration of 2 prisms. As light shine through one, it is refracted into the colors of the rainbow. As the full spectrum of light - the rainbow - travels through the second prism, the waves are recombined into white light. Right: illustration of each wavelength in the spectrum

(Left) Isaac Newton's experiment in 1665 showed that a prism bends visible light andthat each color refracts at a slightly different angle depending on the wavelength of the color.Credit: Troy Benesch.(Right) Each color in a rainbow corresponds to a different wavelength of electromagnetic spectrum.

THE SUN'S CORONA

The Sun is the dominant source for visible-light waves our eyes receive. The outer-most layer of the Sun's atmosphere, the corona, can be seen in visible light. But it is so faint it cannot not be seen except during a total solar eclipse because the bright photosphere overwhelms it. The photograph below was taken during a total eclipse of the Sun where the photosphere and chromosphere are almost completely blocked by the moon. The tapered patterns—coronal streamers—around the Sun are formed by the outward flow of plasma that is shaped by magnetic field lines extending millions of miles into space.

A photograph of a solar eclipse revealing the dramatic coronal streamers that are normally too faint to see over the intense light of the sun's chromosphere.

COLOR AND TEMPERATURE

As objects grow hotter, they radiate energy dominated by shorter wavelengths, changing color before our eyes. A flame on a blow torch shifts from reddish to bluish in color as it is adjusted to burn hotter. In the same way, the color of stars tells scientists about their temperature.

Our Sun produces more yellow light than any other color because its surface temperature is 5,500°C. If the Sun's surface were cooler—say 3,000°C—it would look reddish, like the star Betelgeuse. If the Sun were hotter—say, 12,000°C—it would look blue, like the star Rigel.

Isaac Newton's experiment in 1665 showed that a prism bends visible light and that each color refracts at a slightly different angle depending on the wavelength of the color.

An image of the surface of the Sun appearing warm yellow. A temperature gauge on the left side shows the hotter star Rigel as blue and the cooler star Betelgeuse as red.

Credit: Jenny Mottar; Image Courtesy of SOHO/consortium

a true-color composite of a crater on Mars that looks ruddy brown in color.

The High Resolution Imaging Science Experiment (HiRISE) camera on board the MarsReconnaissance Orbiter (MRO) captured this spectacular visible light image of Victoria Crater.Credit: NASA/JPL/University of Arizona

SPECTRA AND SPECTRAL SIGNATURES

Close examination of the visible-light spectrum from our Sun and other stars reveals a pattern of dark lines—called absorption lines. These patterns can provide important scientific clues that reveal hidden properties of objects throughout the universe. Certain elements in the Sun's atmosphere absorb certain colors of light. These patterns of lines within spectra act like fingerprints for atoms and molecules. Looking at the Sun's spectrum, for example, the fingerprints for elements are clear to those knowledgeable about those patterns.

An image of the full spectrum of visible light - the rainbow - with dark lines appearing in the red, orange-yellow, and green-blue areas of the spectrum. These dark lines indicate that these specific wavelengths are missing and can be aligned to the elements that absorb these specific wavelengths - hydrogen, sodium, and magnesium.

Patterns are also evident in a graph of an object's reflectance. Elements, molecules, and even cell structures have unique signatures of reflectance. A graph of an object's reflectance across a spectrum is called a spectral signature. Spectral signatures of different Earth features within the visible light spectrum ARE shown below.

A graph showing wavelengths in nanometers on the x-axis and percent reflectance on the y-axis. Snow, ice and clouds show a high reflectance across all wavelengths. Dry soil, wet soil, turbid water and clear water all seem to reflect similar values in the blue and green wavelengths, but have very different value closer to red and infrared where soils reflect more than water. Vegetation reflects more in the green and infrared than in the blue and red.

Credit: Jeannie Allen

ACTIVE REMOTE SENSING—ALTIMETRY

Laser altimetry is an example of active remote sensing using visible light. NASA's Geoscience Laser Altimeter System (GLAS) instrument onboard the Ice, Cloud, and land Elevation Satellite (ICESat) enabled scientists to calculate the elevation of Earth's polar ice sheets using lasers and ancillary data. Changes in elevation over time help to estimate variations in the amount of water stored as ice on our planet. The image below shows elevation data over the West Antarctic Ice Streams.

Laser altimeters can also make unique measurements of the heights and characteristics of clouds, as well as the top and structure of the vegetation canopy of forests. They can also sense the distribution of aerosols from sources such as dust storms and forest fires.

Credit: NASA/Goddard Space Flight Center

Next: Ultraviolet Waves

Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Visible Light. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/09_visiblelight

MLA

Science Mission Directorate. "Visible Light" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/09_visiblelight

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