section_path: Scientific career/Old quantum theory/Photons and energy quanta
section_name: Photons and energy quanta
paragraph_text: Photons and energy quanta
  
  In a 1905 paper, Einstein postulated that light itself consists of localized particles (quanta). Einstein's light quanta were nearly universally rejected by all physicists, including Max Planck and Niels Bohr. This idea only became universally accepted in 1919, with Robert Millikan 's detailed experiments on the photoelectric effect, and with the measurement of Compton scattering.
  
  Einstein concluded that each wave of frequency f is associated with a collection of photons with energy hf each, where h is the Planck constant. He did not say much more, because he was not sure how the particles were related to the wave. But he did suggest that this idea would explain certain experimental results, notably the photoelectric effect. Light quanta were dubbed photons by Gilbert N. Lewis in 1926.