Largely owing to these achievements, it
is now possible to generate white light using
LEDs. The three most popular approaches are
shown in Fig. 2a. These are a blue LED with
yellow phosphors; an ultraviolet LED with
blue and yellow phosphors (or red, green and
blue phosphors); and a device that combines
red, green and blue LEDs. Figure 2b presents the spectra for two phosphor-based white
LEDs and sunlight.