Coloured Filters

A pink and yellow exhibit table, with matching white and blue information panel on top. Sitting on top of the table are two square orange frames. One frame has a red see through filter in the centre, the other a blue one.
A pink and yellow exhibit table, with matching white and blue information panel on top. Sitting on top of the table are two square orange frames. One frame has a red see through filter in the centre, the other a blue one.

Certain wavelengths of light are absorbed or transmitted through different coloured filters.

How it works

Look at a picture through a red filter, then a blue filter to observe how light wavelengths can be absorbed or allowed to pass through a filter.

Things to try or ask around the exhibit

  • Do you see the same picture through each filter?
  • How does each filter change what you're seeing?
  • If we used a yellow filter, what would we see in the picture?

Background

Sunlight or indoor light that hits a picture, mostly reflects off the picture's printed ink and travels towards your eyes. Light is composed of different wavelengths, which humans perceive as red, orange, yellow, green, blue, indigo and violet light. If you look at the picture through a coloured filter, that filter will only allow light of its own colour to pass through and will block or absorb other light colours.

For example, if you look at a blue and red picture through a blue filter, only blue light reflected off the blue ink can pass through the blue filter. Red light reflected off the red ink is absorbed or blocked by the blue filter, so red ink in the picture appears black. You are unable to see blue ink through the blue filter, because you cannot distinguish its reflected blue light from the white background (which also appears blue through the blue filter).

The red filter allows red light reflected from red ink in the picture to pass through, while blue light reflected off the blue ink is absorbed and appears as black patterns on a red background.

Finding the science in your world

Coloured filters are used in photography and sunglasses to filter out unwanted colours of light.

Coloured filters are also used in theatres to create certain moods or settings. For example, blue filters may be used to create a night time scene, while yellow filters may be used to create a sunny day scene.