The local control of hydrogen mobility in thin films in combination with an optical indicator which exhibits hydrogen concentration dependent colors allows to visualize hydrogen diffusion in solids. The large mobility of hydrogen in metals and the possibility to tune it over several orders of magnitude makes thin film metal hydrides ideal systems. Planar structures such as prisms can be achieved, allowing to investigate the response of hydrogen diffusion fronts as they encounter these structures. Evidence for refraction-like phenomena at interfaces separating areas of different effective diffusivities are presented. The behaviour of the diffusion front can be described by a modified Snell's law, where the square root of the front mobility in the respective media plays the role of the refractive index. © 2002 Elsevier B.V. All rights reserved.