Once coarse combinations have been found that cover the entire brightness range at nominal temperatures, the PGU must be characterized across all operating temperatures. The goal is to maintain constant performance at all temperatures.

The light output from an LED at a given PWM value will vary predictably with temperature, so the system output must be measured and characterized across many temperatures to ensure consistent white point and PGU brightness at all times. Because coarse combinations stay the same across all temperature sweeps, temperature characterization involves sweeping the LED PWMs for each combination to let the calibration algorithm determine the minimum and maximum PWM values to be stored in the calibration file for each combination and temperature.

These temperature sweeps define the temperature shift characteristics of the LEDs used in the PGU. For the same LEDs, the temperature characteristics of one LED will very closely match those of a second LED. Whether each individual LED is brighter or dimmer at a given current level and temperature, light from all LEDs will change proportionally across all temperatures. This allows the temperature profile to be collected once on a single PGU and mathematically applied to all PGUs during production.

See Section 6.3 for more details on the temperature characterization procedure.