pins 20 to a control unit which dims the ec mirror glass 3 to the necessary extent if a critical luminous value for the glare 12 is exceeded in the same way the mirror glass 3 lightens again if the critical luminous value of the glare is not reached the sensor 5 sends a corresponding signal via the pins 20 to the control unit since the rgb sensor 5 comprises the three layers 16 to 18 corresponding to the primary colours red green blue three different light sources to which one colour filter red green blue is assigned in each case can be detected the colour filters 14 15 are designed so that overlapping of the wavelengths of the light does not occur thus the various light sources 12 13 can be reliably differentiated from each other the colour filters 14 15 are constructed in the known way the light conductors 7 8 are formed so that they catch the light of the respective light source 12 13 without light of the other light source to be detected falling on the light receiving face 9 10 with the arrangements described the luminosity of the ambient light and glare 13 and or 12 can be simply determined using only one sensor 5 and thus in a constructively simple way optimum dimming of the mirror glass 3 is achieved in place of the rgb sensor 5 described a sensor can also be used whose pixels are subject to a colour mosaic filter in this case the pixels only detect one of the primary colours red green blue the actual colour of the pixel is determined by relating to the adjacent pixels also such an rgb.