If we were to perform a double-slit experiment with single photons, how exactly would we know that the detections registered actually are single photons ? If there was no duality, and light was just a wave, then there would have to be a limit on how low intensity we could measure, right ? So how do we know there isn't low intensity waves hitting the detector without triggering it ? Follow-up question: Performing this single photon experiment one assumes that there actually are single photons. The result of this is crazy quantum weirdness. Why is this experiment held as "displaying the non-intuitive nature of QM", and not as "verifying the wave-nature of light" ? ... to me that seems strange.