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Visible Light

by Ron Kurtus (revised 29 June 2002)

Visible light is part of the electromagnetic spectrum of waves. What makes visible light different is that it is a series of electromagnetic wavelengths that we can detect or see. These wavelengths are sensed as colors. Sources of visible light are fires and hot glowing objects.

Questions you may have include:

• How is visible light detected?
• What are its main characteristics?
• How is light created?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

Detecting light

What makes visible light different than the other electromagnetic waves--such as radio waves and x-rays--is that light can be detected with your eyes. This is due to the light causing chemical changes in your retina. Light also can cause electrical and temperature changes in some materials.

Chemical changes

Visible light can cause chemical changes in some materials. One example is how the sun will fade the colors in your furniture. The film in a camera detects light and turns it into the images you see in photographs. Photographic film changes its chemical characteristics according to how much light strikes it.

Electrical changes

Light can also cause electrical changes to occur in some materials. For example, a solar cell creates electricity from light. The retina in your eyes goes through chemical changes that creates electrical impulses when light strikes it.

Temperature changes

Another way to detect light is by observing the rise in temperature of the object. The sun shining on your skin or on some object will cause it to heat up.

Characteristics

Some of the characteristics of visible light are similar to that of all electromagnetic waves.

Speed

Light and all other electromagnetic waves travel at the enormous speed of 186,000 miles per second or 300,000 kilometers per second in a vacuum. They all travel slightly slower through transparent matter.

Wavelengths

Light comes in a spectrum of wavelengths that you can see. Each wavelength is sensed as a color. The basic colors in the spectrum are:

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

These are also called the colors of the rainbow. The way to remember the order of them is the name: ROY G BIV.

When all the colors are combined, you see them as white light.

Materials

Light will pass through some materials, such as glass. Since the velocity of light is slower in glass than in air, the light can be made to bend and even be focused after passing through a glass lens.

Light also can be reflected by shiny materials and absorbed by dark, rough materials.

Creating light

Visible light is created when an object becomes sufficiently hot, as well as from some chemical and electrical reactions.

Hot objects

The Sun is so hot that is gives off visible light. Likewise, a fire is hot, as is the filament in a light bulb.

As the burner on an electric stove gets hot, it first gives off invisible infra-red light, then becomes deep red and finally gives off orange or yellow light when it gets hot enough.

Light from the Moon is actually light from the Sun that is reflected off the Moon's surface.

Chemical or electrical

Some chemical or electrical reactions can create light. A good example of a chemical reaction is the light from a firefly. A light-emitting diode (LED) is an example of an electrical reaction causing light.

Summary

Visible light is the part of the electromagnetic spectrum of waves that you can detect or see. Light's wavelengths are sensed as colors. Other materials and devices can also detect light. Sources of visible light are fires and hot glowing objects.

Answers to Readers' Questions

Light up your life through doing your best

Resources

The following resources provide information on this subject:

Websites

Physical Science Resources

Books

Schaum's Outline of Optics by Eugene Hecht; McGraw-Hill (1974) $16.95

Introduction to Modern Optics by Grant R. Fowles; Dover Publications (1989) $16.95

Optics by Eugene Hecht; Addison Wesley (2001) $108.00 - Textbook covers wave motion, electromagnetic theory, propagation of light, geometrical optics, superimposition of waves, polarization, interference, diffraction, fourier optics and lasers

Miscellaneous

Mini-quiz to check your understanding

1. What type of wave is light?

2. What do different wavelengths represent?

3. Which is hotter: red hot or yellow hot?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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