Methods for mobile robot localization that use eigenspaces of panoramic snapshots of the environment are in general sensitive to changes in the illumination of the environment. Therefore, we propose in this paper an approach which achieves a reliable localization under severe illumination conditions by illumination insensitive eigenspaces. The method in question uses gradient filtering of the eigenspaces. The method was tested on images obtained by a mobile robot and, as we show, it outperforms by far the other known methods.