Junction Temperature Evaluation (I):

Heat is the enemy of all LEDs. Excess heat directly affects both short-term and long-term LED performance. Thermal management is arguably the most important aspect of successful LED system design.

- U.S. Department of Energy

Thermal management has a significant impact on the lifetime, performance and cost of an LED luminaire. The key to a successful thermal management system is to be able to control the junction temperature.

LED efficacy (lumen/W ouput from the light), the most important light engine characteristic will decrease as junction temperature rises. The chart (courtsey of CREE) below shows the relative light output versus junction temperature.

The second most important characteristic, Luminous maintenance (change in light output over the LED life time, normally 70% of the initial lumens) will be reduced as junction temperature increases. The chart (courtsey of CREE) below shows luminous maintenance decreases with the junction temperature increases at constant current (525ma) and ambient temperatures.

The junction temperature will also affect the correlated color temperature and CRI (color rendering index) which represents the true color reproduced form the light fixture. It could be critical for color-sensitive applications