Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The influence of intermediate to high electric fields on the optical properties of direct-gap strongly-polar III-Nitrides is characterized. It is manifested through the dependence on the electric field of the nonequilibrium thermodynamic state of the system, which is characterized by a nonequilibrium effective temperature (quasi-temperature), quasi-chemical potentials and drift velocities of the excited carriers driven away from equilibrium, and the quasi-temperatures of the phonons in the different branches. In particular, we analyze the processes of absorption and luminescence, and a field-dependent Roosbroeck-Shockley relation is derived. It is shown that it is possible to measure the carriers' drift velocity and quasi-temperature, in the steady state or with ultrafast time resolution, resorting to luminescence together with Raman scattering experiments.7216775Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Brazilian National Research CouncilFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)