A MINI-BEAM system incorporates a powerful, modulated LED light source, a sensitive phototransistor, an LED alignment indicator, and a custom-designed, state-of-the-art CMOS modulator/demodulator/amplifier circuit; it features inherently high immunity to ambient light interface. A convenient control enables selection of either light operate or dark operate in the same sensor, and a rugged, 15-turn Gain control allows precise adjustment of sensitivity. A red LED alignment indicator on the rear of the sensor lights to simplify alignment, adjustment, and performance monitoring.