What are runway threshold lights?

Runway threshold lights are lights located at the beginning and ends of the runway to let pilots know where the runway begins. They also alert the pilot, as to how much space remains at the end of the runway, during departure.

The colors of the threshold lights vary in accordance with specific purposes of each light within the runway lighting system. The lights used to alert incoming planes where the runway begins are green, and the lights used to mark the end of the runway are red. Yellow lights indicate that 2,000 feet of runway space remain, and the white lights outline the edges of the runway.