Colours of objects under coloured light beams
STEAM EXERCISE
Related exercises: Colours of objects under filtered light sources 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 illuminated by different coloured LED flashlights.
Colour Concept: The colour of an illuminating light source affects the colour of an object. White LED flashlights emit varying amounts of light across the visible spectrum. Coloured LED flashlights emit light over select wavelength ranges. The perceived colour of objects will change depending on whether the objects are illuminated with white or coloured LED lights.
Materials:
A set of coloured objects – e.g. coloured blocks, tiles from the sorting set, M&Ms, embroidery or spools of threads, etc.
Coloured LED flashlights (red, blue, green)
Mini-stage (optional) or white coloured background
Handout TABLE-Colours of blocks under different sources of illumination
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 red coloured LED flashlight on the coloured blocks. What colour is each block under the red light beam?
Repeat exercise for blue and green coloured flashlights.
Repeat exercise again, this time shining 2 flashlights on the blocks at the same time. Notice the colours of the blocks, and write your answers down in the table.
Document the colours you see through each filter using the Handout TABLE-Colours of blocks under different sources of illumination as 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:
Wavelength, Light
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 block – is the colour of the block affected? (eg blue light beam on blue block)
How do the blocks’ colours in this exercise compare to when they are viewed through coloured filters, in the exercise Colours of objects through coloured filters?
What’s going on?
The characteristics of the illuminating lights are different for each type of LED flashlight. White LED flashlights emit varying amounts of light across the visible spectrum. Coloured LED flashlights emit light over select wavelength ranges. For example, the red-coloured LED flashlights emit light primarily over the long wavelength regions of the visible spectrum. Green LED flashlights emit light primarily over the middle wavelength regions of the visible spectrum. Blue LED flashlights emit light primarily over the short wavelength regions of the visible spectrum. Thus, the perceived colour of objects will change depending on whether the objects are illuminated with white or coloured LED lights.
