@oz1lqo If you want to explore the reflection, the intensity of which depends critically on the angle of incidence of light and the refractive indices of the materials inside and outside, use a blue/violet laser pointer and shine it into a bottle of tonic water. The fluorescence from the quinine shows you the path and relative reflection vs transmission outwards. You can get it to skip round the inside multiple times. Just watch out for stray reflections into your eyes. #demos