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Create coloured shadows!

  • 3 Strong Flashlights
  • Red, Blue and Green Cellophane
  • 3 Rubber bands
  • A clean white board or wall
  • A dark room
  • If you can get your hands on some red, green and blue spotlights use those instead!
  • Optional - a magnifier for focussing the light
  1. Copyright
 
Coloured shadows behind a hand
 

How to make coloured shadows by mixing light

Easy to get materials that make this light science experiment awesome!

  • Coloured shadows behind a hand
  • Red green and blue lights
  • Mixing coloured lights onto a screen
  • Splitting coloured lights with magnifier
  • coloured shadows behind a hand

Instructions

1
Place the red cellophane over the flashlight so that the light is coloured red. Secure with a rubber band.
 
2
Repeat the process, so that you have a 'green flashlight' a 'blue flashlight' and a 'red flashlight' to use.

Red green and blue spotlights
If you can get spotlights, this light experiment is even better!
 
3
Shine all of the flashlights onto the wall - what colour does it make?

Mixing red, green and blue light onto a white screen
Mixing coloured lights during a light & colour science show
 
4
Try shining the flashlights onto your hand or an object, what colour shadows do you make? Why?

Coloured shadows
You should see a dark shadow behind your hand as it approaches the screen
 
5
Try placing a magnifier into the lights to form an image on the white screen of the lamps! As you move the magnifier closer to the white screen you should be able to show the individual coloured light images converge and then mix together.

Using a magnifier with red and blue lights
Using a magnifier during a light & colour virtual excursion

Why does this work?

White light is comprised of all of the colours of the rainbow i.e. the light spectrum.
it is very easy to see this using a glass prism, just like Sir Isaac Newton did in the 1600's

Rainbows coming out of two prisms

Combining the three different colours should have produced a small white area on the wall. 
This is called colour addition i.e. adding up to white light. You used red, green and blue light as they are the primary colours of light.

Your object creates areas where the light from each flashlight cannot pass.
As each flashlight is shining from a different angle some light can still reach the wall, creating coloured shadows. Try pointing a rod or stick in the middle of the focused 3 lights... you should see a magenta, cyan and yellow colour which are the secondary colours formed from the red, blue and green primary colours of light. 

More on light by Museum Victoria.

Variables to try

  • Try different coloured cellophane or lights. Is there a difference between?
  • What happens if you change the colour of the white background?
  1. BACK TO LIGHT EXPERIMENTS
 

INSPIRE, CREATE, EXCITE, INNOVATE!


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