White LED Turning Purple: Analyzing a Phosphor Failure

White LED bulbs are widely used due to their energy efficiency and reliability. However, when operated at high intensities, they can experience unique failure modes. A notable example, highlighted by the electronupdate YouTube channel, involves a Philips MR16 LED spotlight that began emitting a distinct purple light.

Upon disassembling the bulb, it was discovered that the phosphor coating on one of the four LEDs had deteriorated, revealing the underlying 405 nm blue LED. Typically, white LEDs consist of a blue or ultraviolet LED coated with phosphor, which converts the emitted light into a broad-spectrum white light. The degradation of this phosphor layer results in the LED emitting its native blue or violet light, hence the purple hue observed.