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White Light: Definition, Source & Spectrum Video

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  • 0:01 Definition of White Light
  • 1:01 Sources of White Light
  • 1:33 Spectrum
  • 3:48 Lesson Summary
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Lesson Transcript
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 what white light is made up of and how to extract the components of white light through the process of dispersion. You will look at some of the properties of white light, like the spectrum of wavelengths and frequencies that make it up.

Definition of White Light

The electromagnetic spectrum is comprised of a variety of types of electromagnetic waves, each with different wavelengths or frequencies. For example, x-rays, gamma rays, infrared radiation and ultraviolet radiation are examples of electromagnetic waves. Only a small portion of the spectrum of wavelengths can be seen by the human eye. This visible portion of the electromagnetic spectrum is called the visible spectrum. This shows the full spectrum of electromagnetic radiation and highlights the small part of the spectrum that can be called the visible spectrum.

White light is defined as the complete mixture of all of the wavelengths of the visible spectrum. This means that if I have beams of light of all of the colors of the rainbow and focus all of the colors onto a single spot, the combination of all of the colors will result in a beam of white light.

Sources of White Light

White light can be generated by a variety of sources both in space and by artificial sources on earth. For example, the sun and other stars are sources of white light. The sun is the most obvious source of white light in our solar system. As for artificial sources, fluorescent light bulbs and white LEDs produce white light. Other light bulbs, like the incandescent lamp, do not produce white light. They produce light of much longer wavelengths along the yellow to red range.

Spectrum

This illustrates the full electromagnetic spectrum. It highlights just how small the visible spectrum is as compared to the rest of the electromagnetic spectrum. White light is a mixture of all of the visible wavelengths. The full spectrum that forms white light is listed in this table:

Color Wavelength
Violet 380-450 nm
Blue 450-495 nm
Green 495-570 nm
Yellow 570-590 nm
Orange 590-620 nm
Red 620-750 nm

Let's discuss a few key points concerning the visible spectrum, starting with absorption and reflection. Here are a few fun facts about colors and white light. When our eyes detect the color of an object, that means that all other colors of the spectrum were absorbed by the object except for the color you see. For example, when you see a blue shirt, every color except blue was absorbed by the shirt (as a result of pigment molecules of the shirt or any object for that matter). An extreme case would be the color black. When we see black objects, that means that all of the colors of the spectrum were absorbed by the object; hence, nothing is reflected and we see black. Conversely, when we see a white object that means none of the colors of the visible spectrum were absorbed by the object; they were all reflected off the object, and the mixture of those reflected colors gives rise to the white pigment of the object.

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