A human eye can catch one photon
Dark-adapted people can detect a single photon in a laboratory, above chance, and their confidence tracks the trials where the photon was actually sent.
Established2 min read
Hecht, Shlaer, and Pirenne argued in 1942 that a handful of photons could be seen. The 2016 experiment used a quantum light source that sent, on chosen trials, one photon and one photon only. Detection sat above chance, and high confidence lined up with real photons.
A rod cell can start a signal from one photoisomerisation. The brain, on a good night in a dark room, does not throw that signal away. Ordinary rooms drown it.
Caveats
- The result is for trained, dark-adapted observers, not for spotting a photon across a lit kitchen.
Sources
- 1Tinsley J. N. et al.. Direct Detection of a Single Photon by Humans. Nature Communications 7, 2016.