In 1956, the NEC^® required emergency illumination to be “designed and installed that the failure of any individual lighting element, such as the burning out of a light bulb, cannot leave any space in total darkness”. Over time, that language evolved into “emergency lighting systems shall be designed and installed so that the failure of any illumination source cannot leave in total darkness any space that requires emergency illumination.

The intent of 700.16(B) is to ensure that a space requiring emergency illumination is not left in the dark due to something like a lamp failure. Having an emergency luminaire with at least two lamps or having two emergency luminaires in the same vicinity (each with one lamp) ensures that the failure of one will not leave the area in total darkness.

One thing that experienced plans examiners look for is the number of lamps shown on the luminaire schedule in a set of plans. If a single emergency luminaire is shown at an exit door on the lighting layout page, then the plans examiner will be looking at the luminaire schedule to see how many lamps the luminaire type is equipped with to get some sort of a feeling of code compliance with NEC^® 700.16(B).

At final inspection before a certificate of occupancy is to be issued, the inspector often finds two-lamp emergency luminaires that appear to comply with 700.16(B) until a power outage is simulated during the emergency lighting test. During the test, when power is cut to the luminaire the inspector may find that only one of the two lamps in the luminaire is backed up by the internal battery and illuminates upon loss of normal power to the fixture. This is fine as long as there is another emergency luminaire nearby that will illuminate the area requiring emergency illumination so as not to leave that area in total darkness if one of the two illuminated lamps burns out in either luminaire.

If no other emergency luminaire is close by to assist, then this will result in a failed inspection since only one emergency luminaire is present in the area requiring emergency illumination and the luminaire is designed to only illuminate one of the two lamps inside the fixture when normal power is lost.

Below is a preview of the NEC^® (NFPA 70). See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the edition of the NEC^® being enforced.

NEC 700.16(B) System Reliability. Emergency lighting systems shall be designed and installed so that the failure of any illumination source cannot leave in total darkness any space that requires emergency illumination. Control devices in the emergency lighting system shall be listed for use in emergency systems. Listed unit equipment in accordance with 700.12(I) shall be considered as meeting the provisions of this section.