Coloured shadows

When we were playing with our indoor shadows for the second time, I decided to try and make it a bit more fun and colourful with the Christmas lights we used in our recent infinity mirror. The fairy lights are red, green, blue and yellow and I grouped them together into bundles of each colour with elastic bands. What I'd forgotten was that this is almost the classic way to demonstrate how our eyes perceive colour, but I was rapidly reminded of this when we produced cyan, magenta and yellow shadows!

We didn't play with the coloured lights for long, after we'd spent a while with the small boy pretending to be the Sun, and it was a bit of a muddle to try and explain as we had four colours of lights and three objects casting shadows. We simply observed that there were different coloured shadows, and I decided to simplify the setup for the next time to try and explain a little about how the human eye works.

Coloured shadows of the snowman, reindeer and tree

I got my chance the next morning when the smallest member of the family decided to go back to sleep at 7am (before you marvel at this lie in, he'd been up 6 times in the night and the big one was up a few minutes later...!). With the 3 year old alone, and it still pretty dark outside, I decided to give the colours another go. 

The boy chose an object to cast a shadow. I gave him a choice of the shapes we had played with before, but instead he found his Santa tree decoration he received as a present last year. Santa stood in some play dough to hold him up. I put the bundles of red, green and blue lights a few centimetres apart (as far as the wires stretched) on a box to hold them still. I put them at an angle where they shone on Santa and put a cloth around the yellow lights so they weren't visible. 

Santa cast three shadows - one each in cyan, magenta and yellow. I asked what colour the shadows were and the small boy told me red, green and blue without really looking. When I asked him to point to the colours of each as he named them, he realised his error and noticed they were actually blue (cyan), pink (magenta) and yellow. We didn't talk about the bits where they overlap and you see e.g. red. He was a bit puzzled and, if I'm honest, I doubt I really clarified it when I tried to explain that it is because our eyes have sensors (cone cells) which detect either red, green or blue light. So when we see yellow, our red and green cone cells are both detecting some light, and therefore a mix of red and green light also looks yellow. He was more interested in learning the new names of the colours, and that's probably what he will remember from this activity.

Santa and his cyan, magenta and yellow shadows

There are more activities we can try which explore how our vision works and RGB and CMYK colours, so we will revisit this sometime in the new year. For now, if you celebrate Christmas, have a good one, and if not then enjoy a brief break from reading my blog anyway!