I'm confused how reflection and absorption of photons work. For example hydrogen absorbs 4 wavelengths of light, but then that energy is emitted once the electron falls back to its ground state. So does it reflect all other wavelengths and then emit the one it absorbed? Wouldn't that create white light since everything is either emitted or reflected? Also how can photons be converted to heat if absorbing the energy just excites the electron only to emit that same energy right after as another photon?

Are their specific wavelengths light absorbs to excite electrons and wavelengths that just vibrate the electron to create heat? Also how is light reflection and emission not combined to make everything appear white?

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    $\begingroup$ Possible duplicate of How is hydrogen able to emit a light spectrum with only one electron? $\endgroup$ Commented Feb 16, 2019 at 3:30
  • $\begingroup$ That is not the same question at all. My question isn't technically about hydrogen. Just in light absorption and emission in general. Read my actual questions. Why isn't everything white? Since excited electrons from absorbing photons fall back down releasing the same photon it absorbed. $\endgroup$
    – user59323
    Commented Feb 22, 2019 at 21:40
  • $\begingroup$ Then please edit the title of your question. $\endgroup$ Commented Feb 23, 2019 at 14:59

1 Answer 1


Light having most wavelengths passes through hydrogen, rather than is being reflected. And the emitted photons do not necessarily have the same energy as the absorbed photons, due to different causes, such as recoil and hydrogen molecule collisions.

  • $\begingroup$ Moreover the emitted photons won't have the same direction. There are several reasons for why the emerging (passing or reflected) spectrum or lines aren't identical to the impinging one. $\endgroup$
    – Alchimista
    Commented Feb 16, 2019 at 9:31

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