LEDs are solid state light emitters the light is generated inside a small chip.
The light genneration is not 100% perfect so there is a lot of heat generated as well !
The temperature of the chip and the efficiency of light conversion can now be monitored by simple electronic measurements with the LED driver itself.
The quality of the LEDs in production and later at the customer application can now be measured fast, inexpensive and for every single LED.
The first time you can grant a quality and not just promise a quality since quality requires measurements of the product performance.