Runway edge lights showing variable yellow are used in which situation?

Runway edge lights displaying variable yellow are specifically designed to indicate the presence of a displaced threshold. A displaced threshold is essentially a runway marking that indicates where the actual landing and takeoff point is located, set back from the physical start of the runway. The use of variable yellow lights alerts pilots that they are approaching a runway portion that should not be used for takeoffs or landings, thus enhancing safety. This unique lighting is crucial in preventing confusion that could arise from the runway layout, ensuring that pilots are aware of the operational limits pertaining to displaced thresholds.

While low visibility conditions and adverse weather can indeed necessitate specific lighting and markings, the use of yellow lights is more narrowly focused on indicating a displaced threshold rather than being a general requirement for those situations. Similarly, while runway edge lights are critical during night operations, the specific indication of displaced thresholds makes yellow lights particularly relevant in that context.