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Activity

Coloured lights make objects change colour

Summary: 
View a coloured design on cloth or paper under different coloured lights. Understand how the colours of objects change depending on the light they are viewed under.
Science content (2016 curriculum): 
Biology: Sensing, Organ Systems (4, 5, 6)
Physics: Light and Sound (1)
Science topic (2005 curriculum connection): 
Physical Science: Properties of Objects and Materials (grade K)
Physical Science: Light and Sound (grade 4)
Materials: 
  • light that can change colour (LED lights that you can slide between the colours work great)
  • cloth with pattern of different colours, or printed images
  • room that can be darkened
Procedure: 

Turn out the room lights.
View the cloth under different light colours and see how the cloth colours change.
Colours will look their normal colour, a different colour or even black.

The colours appear in the cloth because of the colours (wavelengths) of light they reflect.
If white light hits them (as we usually have with the sun or room lights), the cloth will absorb parts of the white colour spectrum and reflect others - the reflected colours are the ones that we see.
However if only part of the white light spectrum hits the cloth, it is only able to reflect that part of the spectrum. If the cloth is white it will reflect all the colours hitting it, so will look the same as the light colour. If the cloth is another colour, it will still absorb some of the wavelengths, reflect some, and maybe appear a different colour.
For example, a red piece of cloth will reflect red light and absorb all other colours. So if a red light hits it it will appear red, but if a blue light hits it it will appear dark because it absorbs the blue light and reflects no light.
In the photos above, the colours that are fuchsia-coloured in white light (first photo) appear blue in blue light (second photo) and brown in green light (third photo). The pink reflects mostly reds and blues. With blue light hitting it, it can only reflect blue so appears blue. With green light hitting it (a mixture of yellow and cyan), it does not reflect many wavelengths, so appears a darker. Check the last light colour mixing image to see how light colours mix.

Notes: 

I have only done this with a small group. With larger classes it will be hard as everyone wants to control the light colour, rather than just watching. Need to wait for even cheaper LEDS so they can all have one maybe in a shoebox.

Grades tested: 
Gr 4
Gr 5
Teacher: 
Ingrid
Teaching site: 
ingridscience afterschool
Activity originally developed and delivered: 

ingridscience afterschool