Nitride LEDs are universally used for energy-efficient lighting. They are extremely efficient at low indium content and low current density, allowing to produce commercial white LEDs from a blue LED and a phosphor that absorbs blue and re-emits a broad spectrum in the visible range. However, nitride LEDs suffer from a drastic drop in efficiency at higher current densities and higher indium concentrations, for emission in the green or red. This is an obstacle to extending their use, in order to obtain higher efficiencies with less material, as well as better color rendering. These efficiency drops are partly due to an increase in three-particle Auger-Meitner processes, which are strongly impacted by local device heterogeneities, and can be reduced by specific engineering of structural defects in nitride materials. This thesis proposes to study the electronic processes in nitride LEDs in operando, using electro-emission microscopy. In particular, charge injection mechanisms in the active part of the LEDs and Auger-Meitner processes will be investigated and quantified. The spatial resolution of the technique will allow to characterize the role of heterogeneities (defects or alloy disorder) in the loss processes.