This tutorial review highlights recent work on white organic light-emitting diodes (WOLEDs) in view of their potential as the next generation lighting source. It begins with an introduction to the fundamentals of WOLEDs, and then discusses the key factors that determine the performance of WOLEDs. The focus is on charges and excitons, which are the fundamental elements associated with the physical processes within the device. Correspondingly, the third section illustrates how to control the efficiency and color quality of WOLEDs through the management of charges and excitons. Finally, challenges and opportunities for the further improvement of device performance will be discussed.