An improved light collecting efficiency in a projector type automotive headlamp is achieved by including a curved mirror to re-direct light otherwise absorbed by a rear surface of the blocking cut-off shield in “low beam” operating mode of the headlamp. When the shield is moved to a second non-blocking position, a mirror segment conforms to the curved surface of the substantially ellipsoidal reflector to maximize lumen output in “high beam” operating mode of the headlamp. In addition, auxiliary mirror segments may be used to provide a more complete substantially ellipsoidal reflector configuration that maximizes the light collection efficiency. Preferably, the cap holder is purposefully offset in order to position the centerline of the bowed arc of the arc discharge light source in alignment with the optical axis of the optical system in order to maximize light collection efficiency.