RGB LEDs are used in projectors, architectural, display, stage and automotive lighting systems that require efficient, bright output. To produce predictable colors from an RGB LED assembly, each of its component LEDs (red, green and blue) requires individual, accurate dimming control. High-end systems can use an optical feedback loop to allow a microcontroller to adjust the LEDs for color accuracy. Adding a white LED to an RGB LED to produce an RGBW LED extends the hue, saturation and brightness values available in the color system. Each RGBW LED requires accurate dimming of four component LEDs.