The Nature of Light: Origin, Spectrum & Color Frequency

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  • 0:01 Perception of Color
  • 0:32 Visible Light
  • 1:58 Colors in the Spectrum
  • 5:54 Naming the Colors
  • 6:42 Lesson Summary
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Lesson Transcript
April Koch

April teaches high school science and holds a master's degree in education.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

This lesson introduces the basics of visible light and color. Learn how the visible light spectrum is divided into the six color ranges. We'll also discuss why different people name colors in different ways.

Perception of Color

Have you ever wondered if other people see colors the same way you do? If you say that your shirt is blue, and your friends say that your shirt is blue, are they really seeing the same blue that you are? And what about different varieties of blue? Some blues have more of a greenish tinge, while others look more violet. One of your friends might call your shirt teal, while another might call it aquamarine. How do we perceive different colors and distinguish between them? To answer these questions, we'll have to learn more about the visible light spectrum.

Visible Light on the EM Spectrum

The visible light spectrum is a very small part of our giant electromagnetic spectrum. The EM spectrum consists of seven different regions, including x-rays, infrared, and ultraviolet light. The electromagnetic waves that we can see are confined to this small area, called the visible light region. This part of the spectrum is the range of light frequencies to which the human eye is most sensitive. Visible light shares many characteristics with the other EM waves, because it, too, is a type of electromagnetic radiation.

All electromagnetic waves originate from the vibration of charged particles. These charged particles come from a variety of sources, like the sun, other stars, and warm objects like light bulbs and animals. Any source of EM radiation that we can see - like the light from the sun - is considered visible light. So, other sources of visible light would be flames, red-hot metal, and the glowing screen on your cell phone. Our ability to see everyday objects is due to the reflection of light from the surfaces of those objects. For example, the reason you can see your car in your driveway is because the sunlight is reflecting off of it. Your car may be getting very warm in the sun, and it may be giving off infrared radiation because of that warmth. But that's not a form of radiation you can see. You can only see the waves in the visible light region.

Colors in the Spectrum

Recall that the regions in the EM spectrum are distinguished by their ranges in wavelength as well as frequency. EM waves with a large wavelength have a low frequency, and waves with a small wavelength have a high frequency. Visible light spans from about 760 to 380 nanometers in wavelength, which is the same as about 430 terahertz to about 750 terahertz. The low-frequency end corresponds to light that we perceive as the color red. The high-frequency end is related to light that we see as violet. EM waves that are just below the red spectrum are called infrared. These are the waves that have a frequency of less than 300 THz, or more than 1000 nm. We can't see these waves, but we can detect them as heat. At the other end, above the limit for violet light, is the ultraviolet spectrum. Ultraviolet waves have a frequency of more than 1000 THz, or a wavelength of less than 300 nm. We can't see ultraviolet light, either, but we can certainly tell when our skin has been burned by UV exposure.

So, we know the lower frequency limit for red. We know the upper frequency limit for violet. But what happens in between those limits? Where do red and violet transition to the other colors in our visible light spectrum? Red light spans up to about 480 THz, or 635 nm, at which point it transitions into orange. Orange light spans up to 510 THz, or 590 nm. And yellow light spans up to 540 THz, or 560 nm. Do you see how the wavelengths are dropping lower as we increase in value for frequency? That's because for EM waves, wavelength is inversely proportional to frequency. You've seen this on the larger scale of the entire EM spectrum, but it holds true for the tinier bands of colored light on the visible light spectrum.

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Additional Activities

Perceiving Colors

This experiment provides insight on how color is perceived depending on the color of the object and the illuminating light. This also seeks to give a deeper understanding of the absorption and reflection of light.

Key Terms

  • Absorption of light is the process by which light is absorbed on the surface of an object and is converted into energy.
  • Reflection of light is the process of light bouncing back when it falls on the surface of an object.

Materials and Apparatus

  • Cellophane wrapping paper (Blue)
  • White light source (flashlight or desk lamp)
  • Food Coloring (White, Black, Red, Yellow, Green)
  • 5 glasses of water


  1. Find a dark room where the experiment could take place.
  2. Prepare 5 glasses of water and place it in front of the light source (flashlight or desk lamp).
  3. Add each kind of the food coloring to the respective glasses of water.
  4. Take the blue cellophane wrapping paper and attach it to the light source.
  5. Observe the color reflected on each of the glasses of water as it is illuminated with blue light and record your observation.

Follow-Up Questions

  1. Which glasses of water appear blue when illuminated with blue light? Give an explanation for this.
  2. Which glasses of water appear black when illuminated with the same light? Give an explanation for this.
  3. Compare the color that is reflected from the black glass to that coming from the white glass.
  4. What phenomenon of light do you observe when we see a black color reflected from the glass?
  5. What about when you see any other color reflected except black?
  6. How do white and black affect the temperature of an object?

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