Why are only a few emergency lights provided for illumination in subway cars during a power loss?

The reason that only a few emergency lights are provided for illumination in subway cars during a power loss is because they are fed from a battery supply. Emergency lights are specifically designed to operate during power outages, and they rely on a battery backup system to ensure they remain functional when the main power supply fails. This system allows for focused illumination in critical areas, ensuring safety without overwhelming the battery capacity with excessive lighting.

The other options, while potentially relevant in different contexts, do not directly explain the limitation in the number of emergency lights. The cost of the lights, maintenance requirements, and energy consumption are important factors in their design and operation but do not address the primary reason behind providing only a few emergency lights during a power outage. The emphasis is on ensuring reliable and adequate illumination for essential safety purposes while managing the limitations of battery power.