One Photon at a Time

Light does not arrive as a stream you can pour on thicker. It arrives in quanta — indivisible packets, each carrying an energy fixed by its frequency alone. Turning up the brightness sends more packets. It never sends bigger ones. That one sentence is the whole topic.

8 STEPS · 6 QUICK CHECKS · ENERGY PER PHOTON IN 10⁻¹⁹ J · v1