Numerical modeling and uncertainty analysis of light emitting diodes for photometric measurements

Abstract

ABSTRACT With the rapid evolution of new, energy-ecient solid-state lighting (SSL) systems, a requirement has risenfor new performance metrics and measurement methods to address their unique construction and operatingconditions. In this paper, light propagation characteristics in light emitting diodes are analyzed for measurementuncertainty through numerical modeling and simulation. A general 2D EM simulator with PML boundaryconditions is formulated to solve Maxwell's equations using nite-di erence time domain (FDTD) numericalmethod to describe the light propagation in LEDs.A practical GaN LED used in SSL systems is simulated for light propagation. The optical properties ofdispersive materials are modeled using multi-pole Lorentz-Drude model. The input dipole source for the LEDstructure is modeled explicitly through a Gaussian pulse line source at a central wavelength of 460 nm corre-sponding to GaN emission. Finally, the expression for combined standard uncertainty in the light extractioneciency due to uncertainties in inputs such as emission in the active layer and EM elds is developed using theGUM law of propagation of uncertainties. The uncertainty in GaN LED emission wavelength obtained from FullWidth Half Maximum (FWHM) of the emission spectrum is computed to be 16.98 nm. Therefore, the uncer-tainty analysis model is then used to compute the corresponding uncertainties in the LED output measurementsi.e. light extraction eciency, LED output power and EM elds.Keywords: FDTD, LEDs, Optical Metrology, Photometric Measurements, Uncertainty Analysis, Maxwell'sEquations