Runway threshold identification lights, when provided, should be which type of light?

Runway threshold identification lights, which are designed to enhance the visibility of the runway threshold, should emit fixed green light. This type of lighting helps pilots clearly identify the runway's beginning during landing or takeoff, especially in low visibility conditions.

The fixed green characteristic is particularly important as it indicates a designated runway area, guiding pilots accurately to the runway threshold. This feature is critical in maintaining safety and ensuring that aircraft align properly for landing.

Using lights that flash or are colored differently could create confusion, making it harder for pilots to locate the precise start of the runway. Therefore, the use of fixed green lights is specifically tailored to serve this function effectively.