There is described a light extractor (8) for a light guide lamp (1) whose useful surface, that is to say, the surface that, in use, faces the emission surface (5) of the light guide lamp (1), comprises a predetermined distribution of diffusing points (10) and a complementary distribution of reflecting points (9). The light extractor (8) allows obtaining an illumination having preselected features. There are also described methods for determining such a distribution of points so as to obtain a highly uniform illumination.