A white light LED is obtained by coupling a blue LED with YELLOW PHOSPHOR: small variations in the phosphorus thickness, its concentration, composition, and / or deposition conditions can make big differences in chip length, so color tones, and the human eye is staggeringly sensitive to perceiving them.
Unfortunately, it is not possible to precisely reproduce LEDs with identical color temperature, especially for white leds.
To overcome this problem, a process called BINNING is used, by which the LEDs are subdivided into groups with similar color temperatures. The degree of precision required, however, depends on the type of application: these differences are perceived on narrow bundles, while in applications with wide bands (lighting of environments, stamps, etc.) the differences are much less evident.