Phosphor
A yellow coating applied over a blue LED chip that converts part of the blue light into other wavelengths, creating white light. The phosphor blend determines color temperature and CRI.
Almost every white LED is actually a blue LED with a phosphor coating on top. The phosphor absorbs some of the blue light and re-emits it as yellow, green, and red wavelengths. Your eye perceives the combined output as white light. This technique — called phosphor conversion — won Shuji Nakamura, Isamu Akasaki, and Hiroshi Amano the 2014 Nobel Prize in Physics.
The specific phosphor blend determines the color temperature and CRI of the white light. More yellow phosphor creates warm white (2700K). Less phosphor lets more blue through, creating cool white or daylight (5000K+). Premium phosphor blends include rare-earth elements that fill in the red spectrum, pushing CRI above 90 — which is why high-CRI bulbs cost more.
Phosphor degradation is one reason LEDs lose brightness over time. As the phosphor layer ages under heat and light exposure, it becomes less efficient at converting blue to white, causing a subtle color shift toward blue. Good thermal management (heat sinks) slows this process significantly.
Related Terms
- CRI (Color Rendering Index)
A 0-100 scale measuring how accurately a light source reveals true colors compared to sunlight. 90+ is considered excellent.
- Color Temperature
A measure of light appearance in Kelvin (K) — lower values are warm/yellow, higher values are cool/blue-white. Ranges from candlelight at 2200K to daylight at 6500K.
