The the work presented in this paper explores how dynamical light parameters in an outdoor environment can be estimated for use in a real-time augmented reality (AR) system. A method using existing inverse rendering techniques is used to acquire diffuse surface reflectances in an offline procedure. The reflectances are used in an on-line procedure to estimate the illumination parameters of an outdoor scene. The method presented reduces the light estimation problem of outdoor scenes to a modified Phong shading model with two unknown parameters, which can be determined through the use of a linear equations system. The work presented provides an elegant method for estimating dynamically changing illumination parameters without the need for a calibration object in the scene.