Instructions
In this experiment, you will explore what happens when you mix different colours of light. You will need a dark room and a plain white wall (or a large sheet of white paper) to see the results clearly.
- Gather your materials: two torches, a piece of red cellophane, a piece of blue cellophane, and two bands (like rubber bands).
- Take one torch and carefully cover the light with the red cellophane. Use a band to hold it securely in place. You have now made a red light filter!
- Do the same with the second torch, but use the blue cellophane to make a blue light filter.
- Go into your dark room and turn on the torch with the red filter. Shine it on the white wall. Record what you see in the Observations table.
- Turn off the red torch. Now turn on the torch with the blue filter and shine it on the wall. Record what you see.
- Finally, turn on both torches. Shine them at the wall so the two circles of light overlap in the middle. Look closely at the colour created where they mix. Record this in your table.
Our Big Question
What new colour is made when we mix red light and blue light together?
My Prediction
Before you start, write or draw what colour you think you will make when you mix the red and blue light.
Observations
Complete the table below with what you see during your experiment. You can write the colour's name or even use coloured pencils to show what you saw.
| What I Did | What I Observed |
|---|---|
| Shined the torch with the red filter. | |
| Shined the torch with the blue filter. | |
| Shined both torches so the red and blue light overlapped. |
What Did You Discover?
Answer the questions below based on your observations.
- What colour did you create where the red and blue light mixed together?
- Was your prediction correct? (Circle one) YES NO
(Remember, scientists make incorrect predictions all the time! It's part of learning.)
- The cellophane acts as a filter. A filter is something that only lets certain things pass through. In this case, the red cellophane filters the white light from the torch, blocking all colours except for red. What colour do you think the blue cellophane lets pass through?
Think Like a Scientist!
When you mix red and blue paint, you usually get purple. But when you mix red and blue light, you get a much brighter pinkish-purple colour called magenta. Why do you think mixing light is different from mixing paint?
Hint: Think about adding versus taking away. When you mix light, you are adding colours together. When you mix paint, the paint pigments are absorbing, or subtracting, colours.
Answer Key
Observations Table (Example Answers)
- Shined the torch with the red filter: A circle of red light.
- Shined the torch with the blue filter: A circle of blue light.
- Shined both torches so the red and blue light overlapped: A bright pinkish-purple colour called magenta.
What Did You Discover? (Answers)
- Magenta (or bright pink/purple is an acceptable answer).
- This is the student's own answer based on their prediction.
- The blue cellophane lets blue light pass through.
Think Like a Scientist! (Answer Guide)
Mixing light is called additive colour mixing. You are adding different colours of light together to create a new, often brighter, colour. The three primary colours of light are Red, Green, and Blue. Mixing them creates other colours (like red + blue = magenta).
Mixing paint is called subtractive colour mixing. Paint pigments work by absorbing (subtracting) some colours of light and reflecting others. When you mix paints, more light colours are absorbed, and the colour you see is what is left over and reflected to your eyes. This is why mixing paints often results in darker colours.