Polarised—light with a grain direction

Close up of a ‘stressed’ Tesco food bag

Polarisation is something that sounds very technical and complicated, and it is. But it’s also something you can explore at home in an intuitive, hands-on way using things you may well have to hand. The reason for doing so is that it can reveal a hidden world of colour and form.

What you’ll need

• A source of polarised light (a laptop or monitor screen)
• A pair of cinema 3D glasses
• Some bits of clear plastic

A quick intro to polarisation

Light as a wave can be oriented in any direction, but polarised light is oriented in the same direction.The lenses in the glasses you wear to watch a 3D movie are polarised—the left lens is polarised with one direction and the right lens in another, perpendicular to it. The movie is the projected (twice) using polarised filters that match the polarisation of the lenses. Here’s a bit more of an explanation.

A happy by product of this is, if you have a pair of 3D cinema glasses, you can use them to explore polarisation in the world around you.

A Tesco food bag seen through cinema 3D glasses

Different pieces or clear plastic that have been torn or stretched

An injection moulded plastic lid — this is quite dramatic

All of the bits of plastic used in the videos and photos above have been placed in front of a laptop monitor which emits polarised light. If the plastic has been stressed (stretched or torn by yourself, or pressurised in a manufacturing process like injection moulding) those areas will change the polarisation of the light shining through it and create colours which you can see through your 3D glasses.

Putting the glasses on is a magical moment—anonymous, colourless plastic instantly becomes richly colourful and patterned in a way that’s beautiful, but also dense with information about what that material has experienced. If you get the chance I’d encourage you to take a look, it’s truly illuminating.

Just got a hold of a sheet of polarising film, here’s what it can do to the polarised light that comes out from your laptop:

I’m going to look at what else can be done with this film—follow-up post coming soon.

Thanks to Daniel Guedri for getting me on to polarisation—he raised it in his very thoughtful response to the post below on moiré patterns:

Practical magic — the moiré effect