Looking through a red filter

My boys both like looking through transparent but coloured wrappers whenever we have them, and observing how the things around them change colour. I've never really tried to explain what the coloured filter does to the light travelling to their eyes, so I thought I'd set up a simple activity to help us talk about it, and to encourage a bit of reading practice at the same time.

Red filter over blue and red crayon

The easiest source of coloured filters in our house is Babybel cheese with a red wrapper. However I didn't want to have a request for cheese in place of an activity (I swear my boys have a separate cheese stomach, even when they are supposedly full there's always room for cheese, and the youngest one's first two-word phrase was 'more cheese'!) so I actually cut a circle of the wrapper and stuck it between two pieces of cereal packet in the shape of a little magnifying glass!

Making the red filter

When white light, including sunlight reflecting from white paper, passes through the filter, all the colours except the colour of the filter are blocked. When white light shines on red crayon on the paper, red light is reflected. This means that if you hold a red filter between the paper and your eye, you can't see whether there was blank paper or a red crayon drawing because they both look red - the red crayon therefore seems to disappear. However if you have another coloured crayon e.g. blue or green, which does not reflect red light, this appears black when viewed through the red filter as there is no reflected red light to pass through to your eye.

Reading the 'magic E' words

I thought he might like to try and find some hidden words with the red filter. I wrote in blue crayon on white paper the names of animals which his little brother is keen on so I would be able to entertain the little one with some songs and animal noises whilst the big one found the words. I then attempted to disguise these by writing letters around them in various shades of red crayon and by drawing patterns/lines over them too. I thought it was pretty unconvincing as the blue crayon words still seemed pretty obvious to me so I tried a different setup too. He's previously enjoyed finding 'magic E' words using infrared and different black pens, and he's still keen on pointing out magic E in words, so I wrote a selection of such words with blue crayon and added the e in red.

Finding hidden words

I started with the magic E words and he was excited to read them which was a good start. He liked the little red filter, and experimented with placing it over the words and holding it in front of his eye so he could see more of the page at a time. He went through the whole page, sounding out the words with and without the E (I've explained this the way the Alphablocks reading programme does, whereby the vowel says its name rather than its sound if the consonant after it is followed by magic E).

He spotted the other page with hidden words, and asked to have a go.  It turned out they weren't as obvious to him as to me, and he had fun and the little one enjoyed repeated renditions of Old Macdonald's Farm and various animal noises as the big one found and read the words.  All in all, a surprisingly good activity for a simple setup and we talked a bit about the science too, including about white light being made of the colours of the rainbow and the red filter only letting red light through.