What is visible light?

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By Jim Lucas
published

Visible light is the portion of the electromagnetic spectrum that can be detected by the human eye.

A prism splitting white light into the color spectrum (rainbow).
A prism splitting white light into the color spectrum. (Image credit: artpartner-images via Getty Images)
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Visible light is a form of electromagnetic (EM) radiation, as are radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves. Generally, visible light is defined as the wavelengths that are visible to most human eyes.

Electromagnetic spectrum range

The electromagnetic spectrum, from highest to lowest frequency waves.

The electromagnetic spectrum, from highest to lowest frequency wavelengths. (Image credit: Shutterstock)

Visible light is a type of electromagnetic radiation, which is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum. That spectrum is typically divided into seven regions in order of decreasing wavelength and increasing energy and frequency. These regions are:

  • radio waves (wavelengths greater than 0.4 inch, or 10 millimeters)
  • microwaves (wavelengths between 0.004 and 0.4 inch, or 0.1 to 10 mm)
  • infrared (IR) (wavelengths between 0.00003 and 0.004 inch, or 740 nanometers to 100 micrometers)
  • visible light,(wavelengths between 0.000015 and 0.00003 inch, or 380 to 740 nanometers)
  • ultraviolet (UV) (wavelengths between 0.000015 and 0.00003 inch, or 380 to 740 nanometers)
  • X-rays (wavelengths between 4 × 10^−7 to 4 × 10^−8 inch, or 100 picometers to 10 nanometers)
  • gamma-rays (wavelengths less than 4 × 10^−9 inch, or 100 picometers)

Visible light falls in the range of the EM spectrum between infrared (IR) and  ultraviolet (UV). It has frequencies of about 4 × 1014 to 8 × 1014 cycles per second, or hertz (Hz) and wavelengths of about 740 nanometers (nm) or 2.9 × 10−5 inches, to 380 nm (1.5 × 10−5 inches).

Visible light spectrum and color

Diagram of the visible color spectrum. From left (high energy) to right (low energy) it goes gamma rays, x-rays, UV, infrared, and then radio waves.

A diagram showing the visible color spectrum. (Image credit: WinWin artlab via Shutterstock)

Perhaps the most important characteristic of visible light is color. Color is both an inherent property of light and an artifact of the cells in the human eye. Objects don't "have" color, according to The Physics Hypertextbook (opens in new tab). Rather, they give off light that "appears" to be a color. In other words, Elert writes, color exists only in the mind of the beholder.

Our eyes contain specialized cells, called cones, that act as receivers tuned to the wavelengths of this narrow band of the EM spectrum, according to NASA's Mission Science website (opens in new tab). Humans see light at the lower end of the visible spectrum, having a longer wavelength, about 740 nm, as red; we perceive light in the middle of the spectrum as green; and see light at the upper end of the spectrum, with a wavelength of about 380 nm,  as violet. All other colors that we perceive are mixtures of these colors.

For instance, yellow contains light from both the red and green regions of the visible light spectrum; cyan is a mixture of green and blue, and magenta is a blend of red and blue. White light contains all colors in combination. Black is a total absence of light. The first person to realize that white light was made up of the colors of the rainbow was Isaac Newton, who in 1666 passed sunlight through a narrow slit and then a prism to project the colored spectrum onto a wall, according to the website of Michael Fowler, a physics professor at the University of Virginia (opens in new tab).

How does heat energy turn into visible light?

As objects grow hotter, they radiate energy dominated by shorter wavelengths, which we perceive as changing colors, according to NASA's Mission Science. For example, the flame of a blowtorch changes from reddish to blue as it is adjusted to burn hotter. This process of turning heat energy into light energy is called incandescence, according to the Institute for Dynamic Educational Advancement (opens in new tab) (IDEA) website, WebExhibits.org.

Incandescent light is produced when hot matter releases a portion of its thermal vibration energy as photons. At about 1,472 degrees Fahrenheit (800 degrees Celsius), the energy radiated by an object reaches the infrared. As the temperature increases, the energy moves into the visible spectrum and the object appears to have a reddish glow. As the object gets hotter, the color changes to "white hot" and eventually to blue.

Visible light astronomy

This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020. In the first two panels, as seen in ultraviolet light with the Hubble Space Telescope, a bright, hot blob of plasma is ejected from the emergence of a huge convection cell on the star's surface. In panel three, the outflowing, expelled gas rapidly expands outward. It cools to form an enormous cloud of obscuring dust grains. The final panel reveals the huge dust cloud blocking the light (as seen from Earth) from a quarter of the star's surface.

This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020. In the first two panels, as seen in ultraviolet light with the Hubble Space Telescope, a bright, hot blob of plasma is ejected from the emergence of a huge convection cell on the star's surface. In panel three, the outflowing, expelled gas rapidly expands outward. It cools to form an enormous cloud of obscuring dust grains. The final panel reveals the huge dust cloud blocking the light (as seen from Earth) from a quarter of the star's surface. (Image credit: NASA, ESA, and E. Wheatley (STScI))

The color of hot objects, such as stars, can be used to estimate their temperatures, according to IDEA. For example, the sun's surface temperature is about 5,800 kelvin (9,980 F or 5,527 C). The light emitted has a peak wavelength of about 550 nm, which we perceive as visible white light (or slightly yellowish). 

According to NASA, if the sun's surface temperature were cooler, about 3,000 C, it would look reddish, like the star Betelgeuse. If it were hotter, about 12,000 C, it would look blue, like the star Rigel.

Astronomers can also determine what objects are made of because each element absorbs light at specific wavelengths, called an absorption spectrum. By knowing the absorption spectra of elements, astronomers can use spectroscopes to determine the chemical composition of stars, dust clouds and other distant objects.

Orion's bright supergiant star Rigel is in the bottom left. On the right we see the Witch Head Nebula. The Witch Head Nebula is composed of interstellar dust grains reflecting Rigel's starlight making it look blue.

The blue color of the Witch Head Nebula and of the dust surrounding Orion's bright supergiant star Rigel is caused not only by Rigel's intense blue starlight but because the dust grains scatter blue light more efficiently than red. The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen. (Image credit: Mario Cogo (Galax Lux))

Additional resources

Learn more about how the human brain perceives light in this video from National Geographic (opens in new tab). Walk your way through the electromagnetic spectrum with the stunning book "Light: The Visible Spectrum and Beyond (opens in new tab)" (Black Dog & Leventhal, 2013), or do your own visible light experiments at home using guidance from Ducksters (opens in new tab), a children's educational website.

This article was updated on May 23, 2022 by Live Science managing editor Tia Ghose.

Jim Lucas
Jim Lucas
Live Science Contributor
Jim Lucas is a contributing writer for Live Science. He covers physics, astronomy and engineering. Jim graduated from Missouri State University, where he earned a bachelor of science degree in physics with minors in astronomy and technical writing. After graduation he worked at Los Alamos National Laboratory as a network systems administrator, a technical writer-editor and a nuclear security specialist. In addition to writing, he edits scientific journal articles in a variety of topical areas.