Basically, there are four parts to lighting units and lighted exit signs: the lighting heads themselves; the battery; the board that monitors the unit, keeps the battery charged, and transfers the load to battery power in the event of a building power failure; and the housing. Emergency lighting may or may not be incorporated into the exit sign itself. Exit signs themselves may be internally or externally illuminated. Certain exits may also require a visual indicator and an audible indicator in the event of a power failure. Optional fire alarm interfaces cause exit signs to flash when a fire alarm is set off. Generally, facilities use a combination of types of units to create an effective life safety lighting and signage system.

But let’s take a look at what is required by code. Life safety lighting and egress path marking are addressed in the National Fire Protection Association’s (NFPA) Life Safety Code 101, a nationally recognized performance standard for life and fire safety systems.

Adopted by most states as a basis for their mandatory life safety codes -which, of course, vary in their requirements - NFPA 101 spells out general requirements pertaining to illumination of means of egress; emergency lighting, including performance and periodic testing; and signage. It also provides requirements for various types of occupancies.

Among the requirements of NFPA 101:

- Lighting of means of egress under normal conditions must be maintained at a minimum of one foot-candle along the entire path.

- Emergency illumination must be provided for a period of 1.5 hours in the event of the interruption or failure of normal lighting.

- Emergency lighting must provide at least an average of one foot-candle and a minimum of 0.1 foot-candle measured along the path of egress at floor level.

- A functional test must be done on every battery-powered emergency lighting system every 30 days for a minimum of 30 seconds, and once a year for 1.5 hours.

- Means of egress must be clearly marked, with directional exit signs along the paths of egress and exit doors, doors into stairway enclosures, etc. clearly marked; and

- Exit signs must be illuminated, either internally or externally.

Technology Reduces Maintenance

Like most building codes, NFPA provides certain exceptions for existing buildings and signage, as well as for advances in technology. For example, self-testing and self-diagnostic emergency lighting is exempt from the functional testing requirement. With built-in microprocessor diagnostics in each unit, which check the charge and discharge the unit periodically to ensure it will work properly in an emergency, all that must be done is for a maintenance person to walk around and look at the units. If a fault light is on, it needs attention. That takes the place of the actual testing and the written reports.

Some facilities also take advantage of DC-to-AC inverters, which allow ordinary hall lights to serve as egress lighting. In the event of a power failure, inverters switch the lights from building power to battery.