The Strange Behavior of Light

4 min readAug 29, 2021

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An experiment showcasing light passing through polarizing filters

Light is a subject that we are learning more about every day. Whether it’s about how long it would take light to travel through space or its ability to travel without a medium, light has always seemed to amaze us with unique characteristics. One of the interesting characteristics of light that is often looked at is how polarizing films affect it. Here’s a YouTube video titled “The Strange Behavior of Light” posted by “Joy of Curiosity”, explaining the polarization of light:

The “Joy of Curiosity” video explaining and showcasing polarization and the weirdness it brings.

Interesting video, right? Let me simplify the explanation provided in the video with images and explanations:

Before moving onto how light travels through polarizing films, it is important to understand the components that light is made of and how it travels. Light travels as an Electromagnetic wave. This wave is made up of two fields: The Electric field and the Magnetic field. These two fields oscillate at axes that are perpendicular to one another as well as the direction that the light travels towards. These two fields can also be at any angle or direction in space. Now that we have that cleared up, let’s understand the mysterious property that light is exhibiting.

The experiment that is conducted to understand the mystery is done by using a light source emitting unpolarized light and three polarizing filters. A polarizing filter is simply a filter that has many tiny slits that go across its surface. These filters can be rotated to tilt the direction of the slits.

Polarizing filter arranged so the slits are horizontal. Also called “Horizontal polarizing filter”

When utilizing these filters it is important to understand their effect on the light that passes through them: The horizontal polarizing filter, as seen above, horizontally polarizes the light passing through it. Only the horizontal component of light travelling through it at any angle is able to pass the filter. This means that all the light travelling past the filter is horizontally polarized. Let’s understand this with a physical model:

This figure represents light travelling through a horizontal polarizing filter

In the figure above, there are 5 objects that we will focus on for now. “Item A”, labelled with the white “A”, is the light source that is emitting light. “Item B” is a cross-section of the electric field found in an electromagnetic wave. This is showcasing a few of the infinite angles that the electric field can be found in. “Item C” is taking one of these angles into consideration in order to make it simpler for us to understand how the horizontal polarizing filter affects the light. “Item D” is the horizontal polarizing filter that the light is passing through. “Item E” is the horizontally polarized light that is the horizontal component of the specific example we are looking at (“Item C”).

Naturally, the light is reduced when it passes through a polarizing filter; however, the unusual fact has yet to come. If we put a vertical polarizing filter after the horizontal polarizing filter, the light disappears completely. This is because the vertical polarizing filter only allows vertical components of light to pass, but the horizontal light that is passing after the horizontal polarizer has no vertical components. This results in no light passing on.

No yellow paper showcases that no light reaches past the vertical polarizing filter after going through the horizontal polarizing filter

The strange behavior is introduced when we add the third polarizing filter into the mix. This polarizing filter is a diagonal polarizing filter and is tilted diagonally:

Introducing this diagonal polarizing filter between the horizontal polarizing filter and the vertical polarizing filter makes the experiment end result go from no light to some light. This was a shocking discovery made by Paul Dirac in his 1930 textbook The Principles of Quantum Mechanics. Let’s understand what is happening when we add this diagonal polarizing filter.

A diagonal polarizing filter makes the light passing through it become diagonally polarized. Horizontal and vertical light contain diagonal components. When the horizontal or vertical polarized light passes through the diagonal polarizing filter, the resulting light is done by using the diagonal components from them. It results in diagonally polarized light. The diagonally polarized light contains vertical and horizontal components. When this light hits the next filter, the vertical polarizing filter, there is vertical light that is able to pass through.

Image shows how by adding a diagonal polarizing filter between the other two, light reappears

The polarization of light is an interesting concept that is often difficult to grasp. Hopefully, the video in this article along with the images and my explanation made it easier to understand this phenomenal concept. Thank you for reading.

Resources:

The Strange Behavior of Light

Written by Yousuf Ahmad

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