Practical method for measurement of AC-driven LEDs at a given junction temperature by using active heat sinks

Alternating-current (AC) driven high-power light-emitting diodes (LEDs) have become available and introduced into solid-state lighting (SSL) products. AC LEDs operate directly from a mains supply with no need of drivers, and thus can simplify the design of SSL product and potentially increase product's reliability and lifetime. Similar to direct-current (DC) LEDs the optical and electrical properties of AC LEDs are strongly dependent on the LED junction temperature. In addition, the instantaneous junction temperature of an AC LED changes rapidly within an AC power cycle. Accurate measurement of AC high-power LEDs is required for quality control and product qualifications such as the US Energy Star. We have developed a simple, robust method for measurement of high-power AC LEDs at any specified junction temperature under a normal AC operating condition. An active heat sink is used for setting and controlling the junction temperature of the test AC LED. By using this measurement technique, the measurement of an AC LED also obtains the thermal resistance between the LED junction and the LED heat sink.