How does ambient temperature affect LED efficiency? What is junction temperature?

LED fixtures must be designed with junction temperature thermal management as a key component and use the correct LEDs. These products will then be robust enough to operate in most ambient temperature applications. Unlike fluorescent sources, cold temperatures do not impact the performance of LEDs.

Junction temperature is the temperature at the point where an individual diode connects to its base. Maintaining a low junction temperature increases output and slows LED lumen depreciation. Junction temperature is a key metric for evaluating an LED product’s quality and ability to deliver long life.
The three things affecting junction temperature are: drive current, thermal path, and ambient temperature. In general, the higher the drive current, the greater the heat generated at the die. Heat must be moved away from the die in order to maintain expected light output, life, and color. The amount of heat that can be removed depends upon the ambient temperature and the design of the thermal path from the die to the surroundings.