Efficiency droop is the drop in LED efficacy at high current density, caused by carrier losses inside the chip; thermal droop is the drop in output as junction temperature rises. Together they explain why luminaire makers often use many LEDs run gently instead of a few run hard, and why a fixture tested cold on the bench delivers less in a hot ceiling. The hot-to-cold factor in datasheets quantifies the thermal part.
Running those chips at 700 milliamps puts us deep into droop, use twice as many boards at 350 and the efficacy jumps.
Also heard as
- efficiency droop
- LED droop
Related terms
LED
Light-Emitting Diode: a semiconductor light source, made white for lighting by coating a blue chip with phosphor.
Junction temperature
The temperature of the active semiconductor region inside an LED, which governs its output, color and lifetime.
Luminous efficacy
How many lumens a light source or luminaire produces for each watt of electric power, in lm/W.
Driver
The electronic power supply that converts line voltage into the regulated current or voltage an LED needs.