Radio waves, ultraviolet radiation, X-rays and microwaves are some of the forms ofEM radiation. Most human eyes can see the wavelengths that are visible to visible light.

The electromagnetic spectrum, from highest to lowest frequency waves.

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

There are different types of visible light, which are transmitted in waves or particles at different frequencies. The range of wavelength is known as the electromagnetic spectrum. The spectrum is usually divided into seven regions in order of decreasing wavelength and increasing energy. These are the regions.

  • 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)

The range of the EM spectrum is between theIR and UV. It has frequencies between 4 and 8 and cycles per second or hertz.

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)

The most important feature of visible light is color. Light and the cells in the human eye make up color. According to The Physics Hypertextbook, objects don't have color. They give off light that appears to be a color. Elert writes that color is only seen in the mind of the beholder.

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The cones in our eyes are specialized and can be used to tune the wavelength of the narrow band of the EM spectrum. Humans see light at the lower end of the visible spectrum, which has a wavelength of about 740 nm, as red, while we see light at the upper end of the spectrum, which has a wavelength of about 380 nm. The colors that we see are combinations of these colors.

The visible light spectrum has red and green regions and a mixture of red and blue. White light has all colors in it. Black has no light. According to the website of Michael Fowler, a physics professor at the University, the first person to realize that white light was made up of the colors of the rainbow was IsaacNewton, who in 1666 passed sunlight through a narrow slit and then a prism to project the colored spectrum onto a wall

How does heat energy turn into visible light?

As objects grow hotter, they emit energy dominated by shorter wavelength, which we perceive as changing colors. The flame of a blowtorch can be adjusted to burn hotter. According to theIDEA website, incandescence is the process of turning heat energy into light energy.

Incandescent light is produced when hot matter releases a portion of its thermal vibration energy. The energy from an object reaches the IR at about 1,472 degrees Fahrenheit. As the temperature increases, the energy moves into the visible spectrum and the object appears to have a reddish glow. The object gets hotter and the color changes to white hot and 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. The surface temperature of the sun is about 5,800 kelvin. The light has a peak wavelength of about 500 nm, which we think is white light.

The star Betelgeuse would look reddish if the sun's surface temperature were cooler. It would look like the star Rigel if it were hotter.

Astronomers can determine what objects are made of by looking at the absorption spectrum. Calculating the chemical composition of stars, dust clouds and other distant objects can be done with the help of spectroscopes.

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

National Geographic has a video about how the human brain sees light. Light: The Visible Spectrum and Beyond, written by Black Dog and Leventhal, or do your own visible light experiments at home, can be found on the Ducksters website.

The article was updated on May 23, 2022, by Live Science managing editor.

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