1. A method of improving the performance of a monitoring system associated with an aperture, said monitoring system comprising an emitter for emitting radiation adjacent said aperture and a receiver for receiving reflected radiation, said method comprising the steps of: applying a material to a surface adjacent said aperture for altering the intensity of said emitted radiation as reflected from said surface, said material covering at least a portion of said surface; emitting said radiation adjacent said aperture by said emitter; receiving, by said receiver, at least a portion of said reflected radiation from said material; and comparing, by said monitoring system, said received radiation to a threshold value.