The present disclosure provides methods and apparatus for testing light-emitting diodes (LEDs), for example, measuring the optical radiation of an LED. In a method, a pulse-width modulated signal is provided to the LED. One or more characteristics of the PWM signal are varied so as to provide a forward voltage, V.sub.f, corresponding to a target junction temperature, T.sub.j, of the LED. The optical radiation of the LED is measured when the LED obtains the target junction temperature.
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under DE-EE0005877 awarded by the U.S. Department of Energy. The government has certain rights in the invention.