Colours of objects under filtered light sources
STEAM EXERCISE
Related exercises: Colours of objects under coloured light beams and Flag game
Details:
Ages: 10-12 +
Time: 20 minutes
Learning Outcome: Notice and describe the colours seen when different coloured objects (e.g. blocks) are viewed through different coloured filtered light sources.
Colour Concept: Coloured filters absorb certain wavelengths and transmit others. When we look at objects under a filtered light source, the colour of the object can change, because not all wavelengths of light normally reflected by the object when illuminated by white light will be able to reach our eye.
Materials:
Coloured Filter paddle set
A set of coloured objects – e.g. coloured blocks, tiles from the sorting set, M&Ms, embroidery or spools of threads, etc.
White LED flashlight
Mini-stage (optional) or white coloured background
Figure 1. Four coloured foam blocks on mini-stage.
Instructions:
Arrange the blocks on the mini-stage as shown in Figure 1, or your set of chosen coloured objects on a white background.
Turn off the lights and close the blinds in your classroom.
First shine the white LED flashlight through the red-coloured filter on the coloured blocks. What colour is each block under the red-coloured light beam?
Repeat exercise for each of the other filters in the paddle set.
Document the colours you see illuminated by filtered light using the table handout (Colours of blocks under filtered light). This table (or a similar one) is a template for an investigation following the scientific method. (Note: you can create your own version of the table for your specific set of coloured objects.)
Vocabulary:
Questions & observations:
How does the colour of the beam of light illuminating the blocks affect the colour of the blocks?
If you used the same colour of light beam as a block – is the colour of that block affected? (e.g. a blue light beam on a blue block)
How are the colours of the blocks different using the blue vs cyan filters?
What’s going on?
Coloured filters absorb light with a range of wavelengths and transmit others. When we look at objects illuminated by filtered light, the colour of the object can change, because not all wavelengths of light from the object normally reflected when illuminated by white light are reflected. With a different distribution of light reflected to our eye by the object, we experience a new colour perception.
Find out more:
See discussion on How do coloured filters work?
Guess the tile colours shown in this demo by Peter Donahue
