In this paper we present a ray tracing based method for accelerated global illumination computation in scenes with low-frequency glossy BRDFs. The method is based on sparse sampling, caching, and interpolating radiance on glossy surfaces. In particular we extend the irradiance caching scheme of \cite{ward88ray} to cache and interpolate directional incoming radiance instead of irradiance. The incoming radiance at a point is represented by a vector of coefficients with respect to a spherical or hemispherical basis. The surfaces suitable for interpolation are selected automatically according to the glossiness of their BRDF. We also propose a novel method for computing translational radiance gradient at a point.