There is a demo of this in the National Museum of Film and Photography in Bradford, West Yorkshire. It's used to find stress patterns in moulded structures. The demo is really neat. A clear moulded model train bridge has polarised light shone at it and as the model train goes across the bridge, the colour and patterns change as the stress in the bridge changes:) Apart from this and some other really neat demos, there are some great photo's and of course the huge IMax cinema...definately worth a visit:)