2017PF01635 28 ABSTRACT: According to the invention, there is provided a light-based skin treatment device comprising a treatment light source； a treatment light exit window via which, during operation, treatment light generated by the treatment light source is applied to skin of a user, wherein the treatment light exit window comprises an optically transparent material arranged to contact the skin during operation； and an imaging unit comprising an image sensor 5 arranged to generate an image of the skin during operation. The skin treatment device further comprises an optical waveguide comprising a treatment light receiving surface, an imaging light exit surface and a main surface, wherein said treatment light receiving surface is arranged to receive the treatment light so that the treatment light enters the waveguide at the treatment light receiving surface； said main surface comprises the treatment light exit 10 window and is arranged to transmit the treatment light so that the treatment light exits the waveguide at the treatment light exit window； said imaging light exit surface is arranged with respect to the main surface to receive light reflected at the main surface by total internal reflection at positions where, during operation, no skin is in contact with the main surface； said image sensor is arranged to receive from the imaging light exit surface light which is 15 guided by total internal reflection from the main surface towards the imaging light exit surface.L'invention concerne un dispositif de traitement de la peau à base de lumière comprenant une source de lumière de traitement ； une fenêtre de sortie de lumière de traitement par l'intermédiaire de laquelle, pendant le fonctionnement, la lumière de traitement générée par la source de lumière de traitement est appliquée à la peau d'un utilisateur, la fenêtre de sortie de lumière de traitement comprenant un matériau optiquement transparent agencé pour entrer en contact avec la peau pendant le fonctionn
