Do you see ice crystals appear in all sorts of colours? This is possible because of polarised white light. Polarised-what… what’s that? Don’t worry, we’ll explain.
What is polarised light?
Imagine riding along in a car on a street full of potholes. You go straight ahead all the time, and at the same time you’re shaken in all directions, from left to right, up and down. That’s what light rays do too. They go straight ahead, and at the same time they vibrate in all directions. Light rays that only vibrate in one direction are called ‘polarised light’.
What about white light?
White light is actually a mixture of all colours.
Why are the ice crystals coloured?
Polarised white light shines underneath the ice crystals which passes through the ice crystals. The ice crystals deflect all those colours of light in different directions. The light also vibrates in a different direction each time.
If you’re holding the green polarisation filter in front of you, only the light rays that vibrate up and down come through. If you turn the filter a quarter turn, only the light rays that vibrate from left to right get through. As a result, new colours appear when you turn the filters.
What happens if you rotate two polarisation filters in relation to each other?
It suddenly gets dark. One lets rays of light through that vibrate up and down; the other only rays of light that vibrate from left to right… and then, of course, no more light gets through.
Polarisation filter in polarised sunglasses
When you go skiing, it’s best to wear polarised sunglasses. These lenses contain a polarisation filter. They stop a certain type of light rays. Polarised light rays cause a disturbing glare in your eyes when the sun shines on the snow.