A skin or hair treatment device for emitting light radiation with an integrated sensor comprising: a housing; a treatment light source disposed inside the housing of the treatment device for illuminating through a device treatment window a surface, in particular a skin surface, disposed outside the housing in front of the device treatment window, wherein the treatment light source comprises a plurality of light emitting elements arranged on a substrate; a sensor system disposed inside the housing of the treatment device, said sensor system comprising at least one sensing light source for emitting sensing light and at least one light sensor for detecting the sensing light reflected from said surface, wherein the at least one sensing light source and the at least one light sensor are oriented towards the device treatment window; and a control circuit, the control circuit being adapted to control the treatment light source, the at least one sensing light source and the at least one light sensor; characterized in that the sensor system further comprises: a circular polarizer interposed between the device treatment window and the at least one sensing light source and the at least one light sensor; and a shielding (5c, 8, 10) interposed between the at least one sensing light source and the at least one light sensor such that sensing light is prevented from directly impinging on the at least one light sensor without passing the circular polarizer. a housing; a treatment light source disposed inside the housing of the treatment device for illuminating through a device treatment window a surface, in particular a skin surface, disposed outside the housing in front of the device treatment window, wherein the treatment light source comprises a plurality of light emitting elements arranged on a substrate; a sensor system disposed inside the housing of the treatment device, said sensor system comprising at least one sensing light source for emitting sensing light and at least one light sensor for detecting the sensing light reflected from said surface, wherein the at least one sensing light source and the at least one light sensor are oriented towards the device treatment window; and a control circuit, the control circuit being adapted to control the treatment light source, the at least one sensing light source and the at least one light sensor; characterized in that the sensor system further comprises: a circular polarizer interposed between the device treatment window and the at least one sensing light source and the at least one light sensor; and a shielding (5c, 8, 10) interposed between the at least one sensing light source and the at least one light sensor such that sensing light is prevented from directly impinging on the at least one light sensor without passing the circular polarizer. a circular polarizer interposed between the device treatment window and the at least one sensing light source and the at least one light sensor; and a shielding (5c, 8, 10) interposed between the at least one sensing light source and the at least one light sensor such that sensing light is prevented from directly impinging on the at least one light sensor without passing the circular polarizer.