The first technique used in the 1990s to create a pleasant white color was to combine the light output of red, green, and blue LEDs, recognizing that LED light sources are inherently additive. However, each color of the electromagnetic spectrum produced by an LED chip has its own operating requirements and the driver — the bulbs’ controlling circuit board — is relatively complex.

Therefore, the most widely used method of additive mixing to achieve a white light is called a phosphor-converted blue (PCB) type, since the chip, or die, emits a blue color and the protecting lens covering the die has an interior coating of yellow phosphor, absorbing some of the blue light, converting that energy to yellow light. In combination, the resulting mix of color, which is a continuous energy spectrum with one or two peaks, is perceived as “white” light.

A third method, called remote-phosphor technology (RPT), is also slowly gaining acceptance in applications that require uniform illumination, color consistency, and high efficiency, such as downlights, high bay fixtures, and other applications. This method consists of an LED board containing royal blue LEDs, a mixing chamber, and a remote phosphor element. Available in a variety of optics, RTP offers glare reduction, higher system efficiencies, and high optical efficiency for the luminaire.

While phosphor-converted white LEDs are used in many general illumination applications, monochromatic/colored LEDs are also used in a number of applications such as the architectural and entertainment segments of the market.