How LED chips are made

Colour starts in the semiconductor. Red chips commonly use AlInGaP materials. Green and blue commonly use GaN or InGaN. Those layers are grown on a wafer (often sapphire or similar) by processes such as MOCVD, doped into p- and n-regions, and given an active layer where light is made.

Metal contacts form the anode and cathode. The wafer is diced into tiny chips. Each chip is tested for wavelength, brightness, and electrical behaviour, then sorted into bins so a batch stays consistent. Encapsulation (epoxy, silicone, SMD packaging, or a COB pour) protects the chip and shapes the light.

Small shifts in doping, phosphor, or growth conditions change colour and brightness. That is why batching modules from the same LED lot matters on a big wall, and why a random spare from another lot can stick out years later even if it was calibrated on day one.