The Color of Light

Light is a kind of energy  called electromagnetic radiation. There are many different forms of electromagnetic radiation, such as radio waves, microwaves, ultraviolet rays, and X-rays. Each form is characterized by a different wavelength. For example, radio waves can be several miles long, while gamma rays are smaller than atoms.  The light that we see — visible light — falls somewhere in the middle of this "electromagnetic spectrum."

electromagnetic spectrum with different wavelengths diagrammed showing where visible light found
Venn diagram with red, green and blue circles showing secondary colors where they overlap

All the colors we see are combinations of red, green, and blue light.

Visible light may be a tiny part of the electromagnetic spectrum, but there are still many variations of wavelengths. We see these variations as colors. On one end of the spectrum is red light, with the longest wavelength. Blue or violet light has the shortest wavelength. White light is a combination of all colors in the color spectrum. It has all the colors of the rainbow. Combining primary colors of light like red, blue, and green creates secondary colors: yellow, cyan, and magenta. All other colors can be broken down into different combinations of the three primary colors. (If you're mixing material like paint, the primary colors are red, blue, and yellow... but for light, the primary colors are red, blue and green!)

Objects appear one color or another because of how they reflect and absorb certain colors of light. For example, a red wagon looks red because it reflects red light and absorbs blue and green light. A yellow banana reflects red and green light, and absorbs the rest.

See how colored light is reflected and absorbed by different colored surfaces.

What You'll Need

a white paper cup, holiday lights, a pen, and colored markers
  • 1 white paper cup
  • Red, green, and blue markers
  • Strand of brightly colored holiday tree lights
  • 1 pencil or pen

What To Do


Color the inside of a white paper cup with the three primary colors of light: red, blue, and green. Leave one of the stripes white (There should be four equal stripes in red, blue, green, and white.)

coloring one quadrant of the inside of a white cup green
one quadrant colored in green, one red, and in the process of coloring another quadrant blue
inside of white cup showing four quadrants, one white, one blue, one red, one green

Use a pencil or pen to punch a hole in the bottom of the cup.

poking a hole in center of the bottom of the cup

Plug in the strand of holiday lights. Take a red light from the strand and stick it through the hole in the bottom of the cup.

sticking a red holiday light in the hole in the bottom of the cup

Look at the red, blue, and green sections in the cup. (NOTE: For better results, turn off the room light.)

What happens to the colors inside the cup? Do they still look the same, or do the colors in the cup change?

placing the cup with the holiday light in it over the person's eye

Try This!

Try the experiment using the blue and green lights. What happens to the colors inside the cup? Use what you learned about the colors of light to explain why the colors change.

A Sight to Bee-hold!

Human eyes can detect only certain wavelengths, so visible light is the only kind of electromagnetic radiation we can see. Some animals can see other forms of light. Bees and butterflies can see ultraviolet light, which means that they see different colors than we. This helps them find flowers to pollinate. The world must look pretty different from a bumblebee's perspective!

yellow flower seen with human eye

human vision

yellow flower as seen by butterfly where most of flower looks orange and ends of petals pale

simulated butterfly vision

yellow flower as seen by a bee where most of the flower looks green but the ends of petals still look yellow

simulated bee vision

Image Credits:

electromagnetic spectrum, courtesy of AMNH/E.Hamilton; flowers, © Dr. Klaus Schmitt,; all other images courtesy of AMNH