The purpose of the bookmarks for the project Photonics4All is to increase the public awareness of photonics and especially of the technological advances of photonics which have changed and improved everyday life (basic technology introduction). Why do soap bubbles have colour? Light reflects off both the inner and outer surfaces of a soap bubble. As the bubble dries out it changes thickness and the light waves reflecting off both surfaces have to travel different distances. White light is made up of all different colours – or waves of different lengths and - when light waves meet – or overlap - they create different colours. Because reflected light travels different distances due to the different film thicknesses we see iridescence in soap bubbles. This phenomenon is used in photonics to provide anti-reflection coating on your glasses for example.