Plural of photon; tiny particles of light, the smallest units of light energy.
From Greek 'phos' (light) plus '-on' (physics particle suffix). The term was coined in the early 1900s when physicists realized light came in discrete packets.
Photons are weird—they have no mass but carry energy, and they always travel at light speed. Einstein won a Nobel Prize for explaining the photoelectric effect (photons hitting metal), which led to solar cells and digital cameras.
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