Why is electron temperature above ambient/casing temperature in an LED? Why is electron temperature above ambient/casing temperature in an LED? I seem to remember a system of electrons has massive energy even at absolute zero because of the Pauli exclusion principle forcing them to occupy higher energy levels. Does the same reasoning apply here in some way? 
Recombination can result in heating as well, can't it? 
 A: If you have a higher electron temperature  than the crystal lattice or the environment, it is caused by high electric fields of by high intensity light. The joule heating energy input into the electron ensemble has to be balanced by an energy loss to the crystal lattice to maintain a stationary state. At high electric fields the energy input can so high that the random thermal energy of the electrons increases until the energy loss (by phonon emission) leads to a stationary state. One then speaks of "hot electrons". The mean high energy of electrons in a degenerate electron gas, even at very low temperatures, has nothing to do with hot electrons is a semiconductor device.
Note on added question. Electron hole recombination can be an intermediate step in transfer of energy from the hot electron gas to the lattice. If it is radiative recombination energy is transformed into light that might be absorbed again. If it is non-radiative recombination, most of the energy freed by recombination ends up in phonons, i.e., lattice vaibarions.    
