A Novel Differential Method for Power Loss Measurement of White Light Emitting Diodes

The aim of this paper is to build a mathematical model that can be used to evaluate the power loss of a white light emitting diode (LED) without the need for optical power measurements. The model is derived based on sensing the LED power consumption, its heatsink temperature and ambient temperature. According to the fact that the entire power loss of a white LED device is mostly dissipated as heat to the ambient by conduction through its heatsink, this power loss can be evaluated by sensing the heatsink temperature. Thus, a differential method is developed to experimentally quantify the power loss of the white LED. The method is easy to implement and does not require sophisticated optical measuring instruments. In this method, a MOSFET is used as a controlled heating element which is installed on a heatsink identical to the heatsink of the LED-under-test (LEDUT) to provide an indirect way to measure the LEDUT power loss. Another MOSFET is used as an auxiliary heating element to control the LEDUT heatsink temperature and achieve differential temperature measurement. To this end, a power control and measurement system is developed to drive the devices used in the experiment and acquire their voltage, current and heatsink temperature signals. The developed method is tested with a 20 W white LED from Cree©. The experimental results confirmed the effectiveness of the developed method in deriving the parameters of the power loss model of a white LED with a reasonable degree of accuracy compared to mathematical calculations.