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Sugar and sunglasses

By David, 8 August 2019 Activity

Where do these colours come from?

Wearing sunglasses while using a computer might seem like a bad idea. But if you use the right glasses, it can make a great experiment!

You will need

• Computer with an LCD screen
• Polarised sunglasses
• Jar of glucose syrup

What to do

1. Take the label off the glucose syrup.
2. Turn on your computer and find a way to make the screen white. You could change your desktop background, create a blank picture file, open a new document or look up a white picture on the internet.
3. Put on the sunglasses and look at the screen.
4. Tilt your head side-to-side.
5. Hold the jar of glucose syrup in front of the screen and look through it. What colour does it appear? Does the colour change when you rotate the jar? Does it change when you rotate your head?

What’s happening?

Waves of light

You might have heard people talking about light waves. In what way is light like a wave? It’s very similar to a wavy line drawn on a piece of paper. It moves from a start point to an end point, and it has something like height. But it’s even thinner than paper!

Polarising fun

If you’re imagining light waves that are thinner than paper, your polarising sunglasses are like a comb. Paper can fit between a comb’s teeth, but only if it’s turned or rotated the right way.

When light hits your polarising sunglasses and it’s rotated the right way, it passes through to your eyes. If the light hits at an angle, there are two options. Either the light rotates to fit through the polarising ‘comb’, or it’s turned into heat. The closer the light is to the right angle, the more likely it will rotate and go through the sunglasses.

Sunglasses and screens

Liquid crystal display (LCD) computer screens and televisions work using polarising filters, similar to your sunglasses. As a result, the light coming from an LCD screen is polarised. That means all the light is rotated in the same direction.

If your sunglasses are lined up with the screen, it’ll let all the light through. As the sunglasses are rotated, you can ‘turn off’ more and more of the screen’s light!

A bit of sugar

The syrup is made from glucose, which is a type of sugar. Sugar can rotate light waves, but it doesn’t rotate all colours evenly. Your sunglasses will block some colours, and let others through, depending on how much the light has been rotated.

What next?

Feel free to try out this setup on other clear objects too. Do clear plastic objects make cool colours? How about glass, water, or honey?

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