A light guide for a light-based touch-sensitive surface, including first and second curved panels having substantially similar curvatures, wherein light undergoes a first refraction by the first curved panel as it enters the light guide, and undergoes a second refraction by the second curved panel as it exits the light guide, the second refraction being the inverse of the first refraction, and wherein one of the panels is curved in a horizontal plane parallel to the surface and forms a curved rim for the surface.