Color tunable light-emitting diodes with modified pulse-width modulation

In this study, a color tunable light source, operated by a modified pulse width modulation method, is investigated. By utilizing this method along with anti-parallel connected discrete light-emitting diodes (LEDs) and two electrical terminals, a wide range of the chromaticity coordinates is attained and varied by electrical control. Using the combination of a blue LED and a phosphor-converted yellow LED (blue LED plus yellow phosphor), the chromaticity range is varied by electrical control from pure blue to pure yellow. In addition, using the modified pulse-width modulation method and a combination of white and red LEDs, white light with correlated color temperatures ranging from 5000 K to 2000 K is demonstrated.