White LEDs come in two types:
- The blue LED chip is coated with a relatively thin layer of phosphor.
- The blue LED chip is submerged in a small cup filled with phosphor.
The first type of LED emits the same color over its whole emitting area and in all directions. This type of LED has no blue-yellow separation. The second type of LED is significantly cheaper and therefore more common. In most cases the emitted color is still the same in all directions looking from a larger distance. But the LED area that emits blue light is much smaller than the area that emits yellow light. In compact designs, where the lens is close to the LED, the blue-yellow separation occurs. Blue-yellow separation can be minimized by lens design, but cannot always be completely removed.