IEC 60747-5-10:2019(E) specifies the measuring method of the internal quantum efficiency (IQE) of single light emitting diode (LED) chips or packages without phosphor. White LEDs for lighting applications are out of the scope of this document. This document utilizes only the relative external quantum efficiency (EQE) measured at an operating room temperature. In order to identify the reference IQE, an operating current corresponding to the injection efficiency of 100 % is found and the radiative efficiency is determined by the infinitesimal change of the relative EQE at that point. The IQE as a function of current is then calculated from the relative ratio of the EQEs to the value at the reference point, which is called room-temperature reference-point method (RTRM).