An optical vend sensing system for use in vending machines employs a row of light emitters on one side of a region through which a vend product passes during delivery and a row of light detectors on the opposite side. Each detector is substantially aligned with a corresponding one of the emitters, and is capable of receiving light from any of more than one of the emitters when that emitter is activated. The emitters are individually activated in sequential, round-robin fashion and multiple detectors are monitored for each emitter when activated. Interruption of detectible beams between an activated emitter and one of the multiple emitters monitored for the activated emitter. Power applied to an activated emitter is calibrated in steps to a minimum level sufficient to ensure detection by all monitored detectors of light emitted by an activated emitter, plus a safety margin.