Illuminated Footprints™ technology

The CatWalk XT walkway consists of a glass plate on which a mouse or rat traverses from one side of the glass plate to the other side. LED light is emitted inside the glass plate and is completely internally reflected, except at those areas where the animal makes contact with the glass plate, typically the animals’ paws, light is refracted at the opposite site. The high speed color camera that is positioned underneath the glass plate captures these illuminated areas and sends these to a computer that runs the CatWalk XT software.
In addition, if more body weight is exerted on a particular paw, the corresponding footprint area becomes more fully covered by the sole which results in an increase in brightness. This allows subtle differences in pressure between the four paws to be detected. 

Illuminated footprints of a rat traversing the CatWalk XT walkway