How Do We See the Colors of the World?
In autumn green leaves turn to dark orange and red, and a soft rainfall may brighten to a rainbow when the sun comes out. It’s remarkable, when you stop to think about it, that we can perceive color at all. How does that actually work?
Color is no more than a wave of light
Color is defined as the limited range of light that the human eye can see. This is also known as “the visible spectrum of light.” Every color is a wavelength of light. Light travels in waves and scientists can measure each color. Violet and purple have a wavelength of 400 nanometers, blue is 500 nanometers, yellow is 600 nanometers, and red is 700 nanometers. The longer the wavelength, the lower the frequency.
Aren’t all light waves visible? No, they’re not! Visible light is just a small part of what is called “the full electromagnetic spectrum.” Late 18th century scientist James Clerk Maxwell realized that electromagnetism could travel in the form of waves, at the speed of light. This led him to conclude that light itself had to be a kind of electromagnetic wave. Learn more about that here.
The electromagnetic spectrum includes the light waves we can see, and so much more: Gamma rays, X-rays, ultraviolet (UV) rays, infrared (IR), and radio waves (yes, radio waves are made of light.) High-energy gamma waves are about the size of an atomic nucleus and too short for us to see, whereas radio waves are too long for us to see.
But wait––light is both a particle and a wave
In 1905, Einstein won a Nobel Prize for his insight that light is simultaneously both a wave and a particle. With that discovery, quantum mechanics was on its way. It took more than a hundred years for scientists to figure out how to photograph what light looks like as both a wave and a particle. But they did it. Take a look at this beautiful picture, and read about the “photoelectric effect” uncovered by Einstein.
How the human eye perceives color
When light bounces off an object we’re looking at, it first hits the cornea on the surface of our eye. The cornea bends that light towards the pupil, which directs it to the lens. The lens focuses the light to the outer layer of the retina.
The retina houses millions of “rods” that perceive light and dark, and photoreceptors called “cones” that enable us to see color. Cones convert light photons of different wavelengths into electro-chemical signals. The ganglion nerve cells in the inner retina then transmit this information to the optic nerve, which sends it to the brain for interpretation. That’s how you know the delicious crisp apple in your hand is red. Here’s more on how we perceive color.
A rainbow is light refracted through raindrops
Sir Isaac Newton, a 17th century mathematician, was the first to realize that when we break white light apart with a prism, we get the visual spectrum of colored light known as a rainbow––red, orange, yellow, green, blue, indigo, and violet.
In a rainbow, raindrops in the air act as tiny prisms.
A beam of white sunlight enters the raindrop and then bends at different angles in a phenomenon called “dispersion.” The refracted light separates into a rainbow of colors––all at different wavelengths and frequencies. We don’t see colors in pure sunlight (or the light of a flashlight) because when the wavelengths of all colors intersect we only see white.
Here’s more on how rainbows happen!
Interested in games and experiments on optics and light science? Try these