The active regions of ultraviolet light emitting diodes (UVLEDs) for UVB and ultra-violet band C wavelengths are composed of AlGaN alloy quantum barriers (QBs) and quantum wells (QWs). The use of alloy QBs and QWs facilitates the formation of percolative paths for carrier injection but also decreases carrier confinement within the QWs. We applied the recently developed Localization Landscape (LL) theory for a full 3D simulation of the LEDs. LL theory describes the effective quantum potential of the quantum states for electrons and holes in a random disordered system with a high computational speed. The results show that the potential fluctuations in the n-AlGaN buffer layer, QWs, and QBs provide percolative paths for carrier injection into the top (p-side) QW. Several properties due to compositional disorder are observed: (1) The peak internal quantum efficiency is larger when disorder is present, due to carrier localization, than for a simulation without fluctuations. (2) The droop is larger mainly due to poor hole injection and weaker blocking ability of the electron blocking layer caused by the fluctuating potentials. (3) Carriers are less confined in the QW and extend into the QBs due to the alloy potential fluctuations. The wave function extension into the QBs enhances TM emission as shown from a k·p simulation of wave-functions admixture, which should then lead to poor light extraction.