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What is Visible Light? - Wavelength & Spectrum

Instructor: Richard Cardenas

Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.

In this lesson you will learn about the electromagnetic spectrum and where visible light can be found in that spectrum. You will learn about the properties of visible light such as the range of wavelengths and frequencies that make up the visible spectrum.

Definition

Imagine what it would be like to see through the eyes of your dog or cat. What about seeing through the eyes of a bee or a spider? Our world would look very different if we could see through the eyes of animals or bugs because they have their very own range of visible light. In this lesson, when we refer to visible light, we are referring to the frequencies and wavelengths that human eyes can perceive. These wavelengths and frequencies correspond to the different colors that we can detect in everyday things, like the green chalkboard, or your blue car. Anything outside of this range of wavelengths or frequencies is not visible to humans.

Visible light is a kind of electromagnetic wave. Electromagnetic waves are similar to water waves except they can travel through the emptiness of deep space. The figure below shows one wave cycle.

One Wave Cycle
Wave

Any wave is characterized by a wavelength (the distance traveled by the wave during one wave cycle as in the figure above), and frequency, the number of complete wave cycles completed in every second. The sun is a major source of electromagnetic waves (also called electromagnetic radiation), constantly bombarding the earth with waves of different wavelengths and frequencies. In fact, ultraviolet rays (UV rays), which sunscreen protects us from, is also an electromagnetic wave with a different range of wavelengths and frequencies than visible light.

Visible Light and Visible Spectrum

Visible light is just a small part of the complete electromagnetic spectrum. The electromagnetic spectrum is made up of a range of wavelengths and frequencies that are mostly invisible to humans. The figure below shows the entire electromagnetic spectrum.

Electromagnetic Spectrum
EM Spectrum

Of that entire range of wavelengths and frequencies, the portion visible to humans is a very tiny fraction of that spectrum. The table below shows the range of colors and their corresponding wavelengths and frequencies corresponding to the visible spectrum. The units of frequency are Tetra Hertz (THz) or a trillion wave cycles per second, and the unit for wavelength is nano-meter (nm) which is 0.000000001 m.

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