Shop Windows to the Universe

Please help support Windows to the Universe, and our activities to help Earth and space science teachers, with a tax-exempt donation today!
Human eyes evolved in response to the light emitted by the Sun. Thus, our eyes are most sensitive the range of colors from yellow through green.
Click on image for full size
Windows to the Universe original artwork.

Visible Light

Visible light is one way energy uses to get around. Light waves are the result of vibrations of electric and magnetic fields, and are thus a form of electromagnetic (EM) radiation. Visible light is just one of many types of EM radiation, and occupies a very small range of the overall electromagnetic spectrum. We can, however, directly sense light with our own eyes, thus elevating the role of this narrow window in the EM spectrum because of its significance to us.

Light waves have wavelengths between about 400 and 700 nanometers (4,000 and 7,000 ). Our eyes perceive different wavelengths of light as the rainbow hues of colors. Red light has relatively long waves, around 700 nm (10-9 meters) long. Blue and purple light have short waves, around 400 nm. Shorter waves vibrate at higher frequencies and have higher energies. Red light has a frequency around 430 terahertz, while blue's fequency is closer to 750 terahertz. Red photons carry about 1.8 electron volts (eV) of energy, while each blue photon transmits about 3.1 eV.

Visible light's neighbors on the EM spectrum are infrared radiation on the one side and ultraviolet radiation on the other. Infrared radiaiton has longer wavelength waves than red light, and thus oscillates at a lower frequency and carries less energy. Ultraviolet radiation has waves with shorter wavelengths than do blue or violet light, and thus oscillates more rapidly and carries more energy per photon than visible light does.

Light travels at the incredible speed of 299,792.458 kilometers per second (about 186,282.4 miles per second). At this amazing speed, light could circle Earth more than seven times in one second! The lowercase letter "c" is often used to represent the speed of light in equations, such as Einstein's famous relation between energy and matter: "E = mc2". All forms of electromagnetic waves, including X-rays and radio waves and all other frequencies across the EM spectrum, also travel at the speed of light. Light travels most rapidly in a vacuum, and moves slightly more slowly in materials like water or glass.

Last modified July 13, 2005 by Randy Russell.

Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, as well as books on science education!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Electromagnetic Radiation

Electromagnetic radiation is the result of oscillating electric and magnetic fields. The wave of energy generated by such vibrations moves through space at the speed of light. And well it should... for...more

Photon

Light is very strange. Sometimes it is best to think of light as a series of waves. At other times, it is useful to think of light as a swarm of particles. When we think of light as particles, we call...more

Radio Waves

Radio waves are a type of electromagnetic radiation. A radio wave has a much longer wavelength than does visible light. We use radio waves extensively for communications. Radio waves have wavelengths as...more

Saturn's Aurora

Have you ever seen the Southern or Northern Lights? Did you know that Earth isn't the only planet that puts on these beautiful light shows, also known as the "aurora"? Auroral displays have also been observed...more

Hubble Space Telescope

The Hubble Space Telescope (HST) was one of the most important exploration tools of the past two decades, and will continue to serve as a great resource well into the new millennium. The HST is credited...more

The Photosphere - the "Surface" of the Sun

Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (6000 K), so only a small fraction (0.1%)...more

Tools for Math and Science

Some concepts are used in many different fields of science and serve as a general purpose "toolbox" that helps us understand and manipulate ideas across disciplines. These "tools for math and science"...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF