A system is capable of detecting substrates and can differentiate between zero, one, or multiple transparent or semi-transparent substrates in a stack. The system can include an optical sensor, an optically anti-reflective element, and a detector. The optical sensor outputs light towards the optically anti-reflective element. The light detector is positioned to detect light from the light source that is reflected by substrates, if any, positioned within a detection zone between the optically anti-reflective element and the detector.