Planck is a simple science virtual experiment utility, offer you a means of exemplifying how the diode emits light when an electrical current traverses it.
As an ordinary diode, the passage of electric current is significant only when the LED is biased in the forward direction, i.e. the anode to the cathode. Internally there is a potential barrier designated Eg. If the potential difference applied to the LED is less than the minimum required for the electrons to overcome this barrier, there will not be driving. Only when the energy provided by voltage source to the electrons is at least equal to the energy barrier, we will have light
To overcome the potential barrier the electrons can decay in a process called recombination, releasing the energy difference involved that is converted into photon energy. In this condition occurs the emission of light.

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