What type of light indicates the beginning of a runway?

The correct answer is threshold lights, which are specifically designed to indicate the beginning of a runway. These lights are often installed at the runway's threshold, the point where the runway begins and from which takeoffs and landings occur.

Threshold lights are typically white and are important for pilots to identify where they should start their approach for landing or where they can safely begin their takeoff roll. They provide a clear visual reference, which is especially valuable during night operations or low visibility conditions.

Runway edge lights, while relevant, outline the edges of the runway rather than marking the beginning. Taxiway lights serve a different purpose by guiding pilots along taxiways and not indicating runway start points. Strobe lights are generally used for various purposes, including marking certain areas on the airport or on aircraft, but do not specifically denote runway thresholds. Thus, threshold lights are the appropriate designation for identifying the beginning of a runway.