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Visible Light Waves

Look at the light around you: What colors can you see? What shades and shadows dim it? Where is the light coming from? Really focus on all of the light in your visual frame. You’ll notice tons of overlapping and shifting colors. That’s because of the behavior of visible light waves. As we’ll see, the wave-like properties of light are extremely important to how we perceive the earth.

Light on tree.

Light waves shining through the leaves on a tree. Notice how they highlight the leaves unevenly.

Behavior of Light as a Wave

We see light around us all the time. In fact, we only see visible light. Human eyes can’t really pick up anything else. Still, it’s kind of hard to believe that everything is letting off light waves all the time.

Yet, when we learn about the properties of light waves, things make a little more sense. Here are a few examples which we’ll go deeper into: Brightness is determined by the number of waves. Color is determined by the length of the waves. Additionally, waves overlap, changing brightness and color. The list goes on.

The point of these examples is that we can explain what we see around us as the result of wave motion.

Wave Motion, Wavelength, and Frequency

The most important property of a wave is its wavelength. That is, how long a wave is. When waves are released from an energy source (the sun is one), they move outwards in a wavelike motion. It looks similar to that of the following animation.

Simple harmonic motion animation

Notice how the wave seems to ‘reset’ every second or so. It’s the same shape going through a point, over and over again. Well, the length of that shape (a wave) is called its wavelength. Light waves have wavelengths of between 390 and 700 nanometers.

Wavelength is directly related to what we call frequency. It’s how fast a wave moves through a point. Of course, longer waves take longer to go through. So, they have a lower frequency.

How Does This Affect Visible Light?

So far, we’ve learned that light waves have different lengths and speeds. This has a huge bearing on how visible light works.

To start, color itself is the result of wavelength changes. Bluish colors are light waves with a shorter wavelength. Reddish ones are those with longer wavelengths.

Colours

Blue to red, as well as low to high wavelength.

And remember, shorter wavelength gives us a higher frequency. Because light waves transmit energy, higher frequencies mean more energy. A simpler way to say this is that energetic light waves hit something more frequently. This makes it so that blue light has high energy while red light has lower energy.

Other Properties of Light

The Speed of Light

Importantly, light has a fixed speed. That speed is actually the fastest in the Universe. Light waves travel at 186,000 miles per second. That’s unbelievably fast. In space, though, it’s not as impressive. It takes light waves about 8 minutes to go from the Sun to the Earth.

Plane in sky.

This plane is going fast. But lightspeed? Not even close

Reflection and Absorption

Another thing about light is that it’s both absorbed and reflected. Light waves transmit energy to electrons in atoms. This absorption of light causes those electrons to jump to a higher energy level. When they fall back down, the light energy is released as a new wave. This process is called reflection.

Plants in a field.

It’s not easy being green. Plants do all they can to get rid of green light!

Reflection is what decides the color of an object. Color is determined by what wavelengths an object reflects, not what it absorbs. For example, plants are green because they reflect green light.

Interference and Intensity

The last properties of light we’re going to talk about are interference and intensity. These are what determine the brightness of light.

Interference is when two waves mix together. It can lead to a few things. If the two waves are the same and in the same spot, they add together. This makes light more intense. Oppositely, if they’re different (say different colors) they form a new, shorter wave. The resulting light is less bright. It may even be a new color altogether!

Violet light on ocean

We get purple when red and blue light waves interfere with each other.

Other Great Resources:

NASA on the Sun and Visible Light: https://science.nasa.gov/ems/09_visiblelight

Ducksters on the Light Spectrum: https://www.ducksters.com/science/light_spectrum.php

Physics4Kids – Optics and Visible Light: http://www.physics4kids.com/files/light_visible.html

More Facts About the Visible Spectrum: https://easyscienceforkids.com/visible-spectrum-video-for-kids/

Light is Waves: Crash Course Physics:

 

Written by: Noah Louis-Ferdinand.