What criteria must emergency exit signs meet according to building standards?

Emergency exit signs play a crucial role in ensuring safe egress during emergencies, and their criteria are strictly outlined in building codes and standards. The correct answer emphasizes that emergency exit signs must be both illuminated and visible. This is essential because in a crisis situation, visibility can be severely compromised due to smoke, darkness, or panic among occupants. Well-illuminated exit signs provide clear direction and help guide people to safety quickly and efficiently.

Illumination ensures that the signs can be seen in low-light conditions, while the visibility aspect relates to their placement and size, making them easily recognizable from a distance. This compliance with standards is vital for ensuring the safety of building occupants and is a fundamental requirement in both local and national building codes.

The other options provided do not align with the primary requirements for exit signs. While having reflective surfaces or solar power might be beneficial in specific contexts, they are not mandated criteria. The installation of signs at all entrances is also not required; rather, they need to be strategically placed to ensure effective exit routing in emergency situations.