Understanding and evaluating the mean photon energy and the external quantum efficiency of light-emitting diodes

The mean photon energy of a light-emitting diode (LED) as recently defined in the IEC standard is theoretically examined. It is pointed out that defining the mean photon energy as an arithmetic mean of photon energies in the emission spectrum is crucial in decomposing the power efficiency of an LED into the voltage efficiency and the external quantum efficiency (EQE). The mean photon energy thus defined and the photon energy calculated from the more convenient peak wavelength in the spectrum are then evaluated and compared for blue and red LED samples. The EQEs of the blue and red LEDs are subsequently obtained, demonstrating that the EQE values from the peak photon energy have small errors within 0.5%p of the true EQE values. The current work presents useful criteria in substituting the EQE value calculated from the peak wavelength for the true EQE value using the mean photon energy for both the blue and red LEDs.