How is the emergency lighting in the cabin powered?

The cabin emergency lighting is powered by the emergency battery, which serves as a backup source of power specifically designed for situations where the main electrical system fails. This is crucial during emergency scenarios, ensuring that the cabin remains illuminated and allowing for safe evacuation procedures. The emergency battery is engineered to automatically activate when a loss of electrical power occurs, providing immediate light in critical areas to enhance visibility and safety.

While other options may offer power under normal circumstances or for different systems, they do not guarantee illumination during an emergency. The main battery typically supports general aircraft systems, GPU (Ground Power Unit) power is used mainly on the ground for operations while the engines are not running, and ground power is not meant for use during in-flight emergencies. Thus, the emergency battery is specifically designed as a reliable power source for emergency lighting, making it the correct choice for this question.