What activates the cabin altitude warning lights?

The cabin altitude warning lights are specifically designed to alert the crew to situations where the cabin altitude exceeds safe levels. This typically occurs when there is a failure in the aircraft's pressurization system or a rapid decompression event. When the cabin altitude rises above a predetermined threshold, the warning lights are activated, indicating to the crew that immediate action may be required to ensure passenger and crew safety.

The focus is on the excess cabin altitude, as this indicates that the pressure inside the aircraft is not being maintained at a level suitable for breathing. Other options, while they might indicate issues related to the aircraft's systems, do not specifically pertain to the activation of the cabin altitude warning lights. For instance, low cabin pressure might suggest a problem, but it is the excessive cabin altitude condition that directly triggers the warning lights.