Principles of LED Headlights

White LEDs operate based on several different principles; Figure 1 illustrates three typical examples. The "blue LED + yellow phosphor" type shown in Figure 2a represents the state-of-the-art in white LED development and is the most likely candidate for first-generation LED automotive headlight systems. The "UV LED + RGB (red, green, blue) phosphor" type shown in Figure 1b holds the greatest potential for general lighting applications due to its high color rendering index; however, its use in headlight systems requires addressing the issue of UV-induced aging in plastic components. The "RGB three-chip" type shown in Figure 1c offers the capability to adjust the emitted light color, yet it is currently unsuitable for headlight systems because it is difficult to prevent color shifts during operation-shifts that may stem from differing temperature characteristics among the three chips or varying rates of degradation across the different LEDs.