The invention relates to a mouthpiece (100) for illumination of teeth, e.g. for teeth whitening. The mouthpiece is configured with at least two lenses (102a, 102b) shaped to cast asymmetrical light onto the teeth (110). The lenses are arranged one-to-one with associated light sources (101a, 101b). The first and second lenses are arranged to project the received light onto a buccal side (111) of the teeth (110), and each of the first and second lenses has an asymmetrically shaped refraction surface (301) shaped to change an intensity distribution of the received light asymmetrically on opposite sides of an optical axis (121) of the respective light source along the dental arch (201) of the teeth.
