You’ll need

  • An RGB LED light globe (you can buy these for about $10). If you can’t find one, try using some coloured fairy lights.
  • A flexible light cord that you can plug the globe into, about 2 m long
  • A white bin with lid, about 15 L
  • A large black shirt or black material (optional)
  • A range of coloured objects, like small toys or plastic figures
  • White paper
  • Highlighters and coloured markers

What to do

Warning!

Fluorescent and incandescent globes can get hot and burn you when you touch them. Use LED globes because they don’t get hot.

  1. Open the lid of the bin and place different coloured objects in the bottom.
  2. Hold the light globe (or a few fairy lights) inside the bin, but have them hanging near the top. Close the lid of the bin as much as possible to stop outside light getting in.
  3. Switch the light globe (or fairy lights) on and look inside the bin. If there is too much outside light, you may want to cover yourself with the black shirt or material as you look inside the bin.
  4. Change the colour of the light globe using the remote control. See if the different colours change how the objects look.
  5. Try the experiment again, but instead of different coloured objects, write messages on paper using highlighters and coloured textas and put them in the bottom of the bin.

Questions to ask

What happened when the objects were under different colours of light? Did they appear to change colour?

Did some objects appear to change colour more than others? Why do you think this is?

If you write messages with different coloured textas, can you make your message disappear? Why do you think the message disappears?

Can you work out how we see different colours? What coloured light do we need to ‘see’ the different-coloured objects?

What's happening

The visible light spectrum (the light the human eye can see) covers a range of wavelengths, which we see as different colours. Low-energy light appears red, while high-energy light appears violet.

The colour of an object is not a part of the object. In fact, the colour we see depends on the light that is shining on the object, and the light that is reflected off the object. For example, a granny smith apple isn’t green; when we see the apple under sunlight (light that contains all colours), the green light (or wavelength we see as green) is reflected, while all other colours are absorbed. Because green light is reflected, that is the colour we see. An object that reflects all colours looks white, while an object that absorbs all colours looks black.

This only works because sunlight contains all colours. If you shine a light that only has one colour on an object and that object absorbs that colour, the object will look black. For example, if we shone a red light onto the green apple, all of the red light would be absorbed by the skin of the apple and no light would be reflected, making the apple appear black. This is why shining different-coloured lights on coloured objects makes them change colour.