Emergency lights can install on tabletops, walls, or remain portable. To figure out the number of lamps you need in a space, consider the size of the space and the foot candle created by each lamp head. Most building codes require at least one foot candle per square foot. Building codes may also require a specific length of time the light needs to operate without power, and backup systems when performing maintenance. To avoid code violations and fines, always have a professional install and perform maintenance on emergency lights.