according to the invention, a light-based skin treatment device is provided which comprises a source of treatment light； a treatment light exit window through which, during operation, the treatment light generated by the treatment light source is applied to a user's skin, the treatment light exit window comprises an optically transparent material, arranged to come into contact with 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 output surface and a main surface, said treatment light receiving surface is arranged to receive the treatment light so that the treatment light enters the waveguide on the treatment light receiving surface； the main surface comprises the treatment light exit window 10 and is arranged to transmit the treatment light so that the treatment light leaves the waveguide in the treatment light exit window； the imaging light output surface is arranged in relation to the main surface to receive light reflected on the main surface by total internal reflection in the positions where, during operation, no skin is in contact with the main surface； the image sensor is arranged to receive light from the imaging light output surface which is guided by total internal reflection from the main surface towards the imaging light output surface.de acordo com a invenção, é fornecido um dispositivo para tratamento de pele à base de luz que compreende uma fonte de luz de tratamento； uma janela de saída de luz de tratamento através da qual, durante o funcionamento, a luz de tratamento gerada pela fonte de luz de tratamento é aplicada à pele de um usuário, a janela de saída de luz de tratamento compreende um material opticamente transparente, disposto para entrar em contato com a pele durante o funcionamento； e uma unidade de imageamento que compreende u
