A vehicular interior rearview mirror assembly includes an electro-optic reflective element, a photo sensor and a light concentrator. The electro-optic reflective element has a front substrate with a first surface and a transparent second surface electrically conductive coating disposed on a second surface, and the electro-optic reflective element has a rear substrate with a third surface transflective metallic reflector disposed at a third surface thereof. The photo sensor is disposed behind a fourth surface of the rear substrate and operable to detect light passing through the transflective metallic reflector and the electro-optic reflective medium disposed between the second and third surfaces. The light concentrator is disposed between the photo sensor and the fourth surface of the rear substrate, and the light concentrator receives light passing through the transflective metallic reflector of the electro-optic reflective element and concentrates light onto a light sensing surface of the photo sensor.