White light is not pure white. It's a mixture of different colours. When they are brought together it looks white. We can split the light to see the different colours in it. I will show you.
Here we can see the white light. Can we have the main light off please?
(Colin is showing the path of white light going through different optics and then you can see the light is now split into different colours after passing through the prism.)
First of all, the white light goes through a slit and then through a lens. The rays are now parallel and they hit a prism.It's a triangular prism. The glass in the prism will make the rays of light refract. The prism makes the different colours refract at different angles. The refracted light now goes through another lens. The visible spectrum is now showing on the white screen. Red is over on the far left. It has the longest wavelength and it refracts to the left. Blue is on the far right. It has the shortest wavelength and the light refracts more to the right. You can see all the colours on this white screen.
Going from left to right we have red, orange, yellow, green, blue, indigo and violet.