Systems and methods for determining the area of a sash opening in a fume hood formed by at least one movable sash panel. An emitter and sensor panel is mounted in a fume hood enclosure space. The emitter and sensor panel comprises at least one light emitter mounted on one side of an optical sensor. The at least one light emitter is configured to illuminate the fume hood enclosure space. At least one reflective marker is mounted on one edge of the sash opening to reflect light from the at least one light emitter. Optical information detected at the optical sensor is used to determine a variable distance to the at least one reflective marker. The variable distance and known distance parameters are used to determine the area of the sash opening.