What is the minimum intensity in footcandles for the face of an externally illuminated exit sign?

The minimum intensity for the face of an externally illuminated exit sign is established at 5 footcandles. This level of illumination is critical to ensure that the exit sign is clearly visible in a variety of conditions, especially in emergency situations when visibility can be compromised.

An intensity of 5 footcandles is sufficient to make the sign legible and recognizable from a distance, promoting safe egress in a commercial building. Requirements like these are outlined in building codes and standards related to safety in order to provide guidance for emergency preparedness. By having a minimum illumination level, it ensures that all individuals can identify exit paths effectively, reducing the likelihood of confusion or accidents during an emergency evacuation.

Other intensity levels—like 1, 3, or 7 footcandles—do not meet the necessary criteria for safety. Lower levels may be too dim to ensure visibility, while a higher level might not represent standard compliance, leading to potential over-illumination or increased operating costs. Thus, a minimum of 5 footcandles strikes the appropriate balance for effective emergency signaling.