LEDs are current driven devices of which the light output is supposed to be proportional to the current flowing through the p-n junction. When a higher drive current is applied to LEDs, there is increased light output. Since the costs of LEDs scale approximately as chip area, increased lumen output from LED light sources lowers the cost per lumen of LED lighting systems. However, the relationship between light output and drive current is non-linear. At low power density LEDs fabricated from InGaN can achieve a high internal quantum efficiency (IQE). As the current density is raised beyond the saturation level, the IQE of the LED is reduced due to a phenomenon known as efficiency droop or current density droop. The droop is dependent on the carrier concentration in the active region of the LED. At higher current density operation, the rate of non-radiative Auger recombination increases. Auger recombination releases energy in the form of heat (phonon, thermal energy), rather than light (photon, radiant energy).
Driving an LED harder can increase its light output, but the LED can no longer maintain its high efficiency as it does at lower current density operation. A large amount of Auger recombination inside the light-emitting quantum wells (QWs) results in a substantial amount of heat trapped in the LED package. The atomic defect generation and growth in the active region of the diode can be accelerated at higher temperatures. Excessive heat causes degradation of materials utilized in the LED package, such as phosphors and encapsulatant. Thermal degradation over the time leads to premature lumen depreciation and color shifts. For high power LEDs that have non-homogenous distribution of the current density across the LED active region, high drive current operation can lead to current crowding, posing risks of thermal runaway. As a result, overdriving what the LED is rated for will eventually reduce the useful life of LED packages.
Driving an LED harder can increase its light output, but the LED can no longer maintain its high efficiency as it does at lower current density operation. A large amount of Auger recombination inside the light-emitting quantum wells (QWs) results in a substantial amount of heat trapped in the LED package. The atomic defect generation and growth in the active region of the diode can be accelerated at higher temperatures. Excessive heat causes degradation of materials utilized in the LED package, such as phosphors and encapsulatant. Thermal degradation over the time leads to premature lumen depreciation and color shifts. For high power LEDs that have non-homogenous distribution of the current density across the LED active region, high drive current operation can lead to current crowding, posing risks of thermal runaway. As a result, overdriving what the LED is rated for will eventually reduce the useful life of LED packages.
