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I'm having a little trouble understanding as to what the voltage drop across an LED actually does in terms of the electrons. I understand that the potential difference across an LED causes the electrons to move and then undergo recombination to emit light, but why does it only happen significantly at a certain potential difference. What happens at lower potentials?

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    \$\begingroup\$ Possible duplicate of How does the current limiting resistor for an LED affect current and voltage drops? \$\endgroup\$ – Passerby Nov 24 '15 at 5:33
  • \$\begingroup\$ @Passerby This question clearly isn't a duplicate of that one - this one is asking about the physics of how LEDs operate, not about current limiting with resistors. \$\endgroup\$ – Nick Johnson Nov 24 '15 at 8:00
  • \$\begingroup\$ @nick the answer for that question has a much better explanation on how diodes work, including current vs voltage. That graph especially. \$\endgroup\$ – Passerby Nov 24 '15 at 8:03
  • \$\begingroup\$ @Passerby He's not asking how the forward voltage varies with current, though. He's asking "why does it only happen significantly at a certain potential difference" and "what [it] actually does in terms of the electrons". \$\endgroup\$ – Nick Johnson Nov 24 '15 at 10:45
  • \$\begingroup\$ hmm. Okay, retracted. The quality of this answer is lacking still. \$\endgroup\$ – Passerby Nov 24 '15 at 11:04
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An LED is a diode. A diode is a semiconductor. At potentials lower than the forward biased voltage drop, very little current would be flowing. As the potential rises, more current is able to pass through (exponentially).

For more information, research semiconductor doping.

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