Light-emitting diodes (LEDs) have been used for some time in interior vehicle applications such as instrumentation panels, but it has only been within the past five years that they have become viable for exterior lighting. This paper provides an overview of LED technology and the significant economic and performance advantages it offers compared with incandescent lights. It traces the evolution of the technology from its commercial introduction nearly 30 years ago through the latest advances in efficiency and color. Also addressed are specific issues relating to its application to trucks and buses and the challenges arising from developing lighting systems that are designed to last for the lifetime of the vehicle. The appendix provides a methodolgy for calculating return on investment (ROI) in LED lighting.