The ubiquity of mobile devices with powerful processors and integrated video cameras is re-opening the discussion on practical augmented reality (AR). Despite this technological convergence, several issues prevent reliable and immersive AR on these platforms. We address one such problem, the shading of virtual objects and determination of lighting that remains consistent with the surrounding environment. We design a novel light probe and exploit its structure to permit an efficient reformulation of the rendering equation that is suitable for fast shading on mobile devices. Unlike prior approaches, our shading probe directly captures the shading, and not the incident light, in a scene. As such, we avoid costly and unreliable radiometric calibration as well as side-stepping the need for complex shading algorithms. Moreover, we can tailor the shading probe's structure to better handle common lighting scenarios, such as outdoor settings. We achieve high-performance shading of virtual objects in an AR context, incorporating plausible local global-illumination effects, on mobile platforms.