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.
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:
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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Now let's discuss prisms and rainbows. Another interesting thing about white light is that it can be split up into its individual colors. A prism is a device that can separate white light into its different colors. When white light goes through a prism, the light bends because the speed of light decreases as it goes from air to the prism. The speed of light depends on the wavelength of the light. As a result, when white light bends through a prism, each wavelength travels at a different speed inside the prism, resulting in the different colors emerging from the prism. This is the same reason why we have rainbows. The white light from the sun bends through the drops of rain, which act like many tiny prisms. As a result, each of the white beams of light going through the rain separate into the different colors and, collectively, they combine to form a rainbow.
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.
When you mix all of the wavelengths of the visible spectrum, you get white light. The sun and many objects in space are good natural sources of white light. On earth, fluorescent light bulbs and white LEDs are artificial sources of white light. Devices like prisms can be used to separate white light back into the different colors of the visible spectrum.
Key Terminology from the Lesson
Electromagnetic Spectrum: variety of differing electromagnetic wavelengths/frequencies
Visible Spectrum: those wavelengths that can be seen by the 'naked eye'
White Light: the combination of all the visible wavelengths
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