How would a runway controller alert aircraft to vacate the landing area?

The most effective method for a runway controller to alert aircraft to vacate the landing area is by showing red flashes on the signalling lamp. This visual signal is widely recognized in aviation as an immediate and clear indication that an aircraft should vacate the runway or landing area.

Using red flashes is a standard practice because it provides a high level of visibility, especially in various weather conditions or times of low light. Additionally, this method adheres to established aviation protocols and ensures that all pilots and crew are aware of the need for quick action. Other options, while they may be useful in specific contexts, do not carry the same urgency or recognition as the red flashing light, which is specifically designed for critical notifications like this one.