Dresden 2017 – wissenschaftliches Programm
HL 25.7: Poster
Montag, 20. März 2017, 15:00–19:00, P2-OG2
CW and Pulsed mode Characterization of LED — •Laveen P. Selvaraj, Thomas Hünnerkopf, Matthias Wachs, and Ulrich T. Schwarz — Chemnitz University of Technology, Experimental Sensor Science, Reichenhainer str. 70, 09126 Chemnitz, Germany
Lambertian source LEDs are most commonly used for lighting applications, with an angular intensity distribution following a cosine law with respect to the viewing angle of the emitting surface . The current investigation deals with the characterization of standard Lambertian LED sources using Continuous Wave (CW) and Pulsed mode. In CW mode, a DC bias current was applied to measure the low current range with long source-on time (>0.2 s) with high sensitivity. For high currents, the pulsed mode was used at a low duty cycle to limit heat generation. The total flux emitted was calculated by integrating the peak intensity with Lambert’s cosine law. The emission rate in normal direction was determined by a photodiode. We use this setup to measure the standard current-voltage (IV) and current-optical output power (IP) characteristics as reference for other measurements. Non-thermal efficiency droop of LEDs at high currents densities, which is caused by non-radiative recombinations, is observed as well as thermal droop . The effect of heat generation on the IP and IV characteristics can be observed by varying the duty cycle of the pulsed mode at high currents. References:  A. Ryer, Light Measurement Handbook. International Light Inc., Technical Publications Department, 1997.  E. F. Schubert, Light emitting diodes. Cambridge University Press, 2003.