With the exception of private residences, most occupancies and facilities are required to provide emergency lighting. Specifically, national, state, and local building codes, including the NEC, the NFPA’s Life Safety Code (LSC), and OSHA, require reliable and sufficient emergency illumination for all commercial, industrial, and institutional buildings in the United States.
In the event of an emergency situation, such equipment should provide continuous illumination for a minimum of 90 minutes to allow people to exit a building through passageways, corridors, stairs, ramps, and escalators. The illumination from emergency lighting should be designed to safely guide occupants to the nearest path of egress and prevent injury.
In most cases, emergency lighting systems are powered by either battery-powered equipment or back-up emergency generators. Both power methods have distinct advantages, and as a result, they’re suitable for separate uses. Battery-powered back-up systems are capable of starting virtually instantaneously, which is crucial in emergency situations. However, they don’t offer the longevity of gen-set-powered systems, which is necessary for longer duration outages. Traditionally, gen-sets took considerably longer to power-up, creating a comparatively substantial dark period when light is critical to safe exit. New devices and lamps are shortening that switching time, helping gen-set-powered systems approach the instantaneous nature of battery-powered systems.
Battery-powered systems. Several battery-powered emergency lighting options exist for facilities that need instantaneous lighting in the event of a power failure.
If you select a battery-powered lighting unit, make sure you know the difference in operation and legal requirements between emergency lighting and other types of battery backup systems. Emergency lighting systems are UL-Listed as Life Safety Equipment. Therefore their construction and performance must adhere to very stringent requirements. Emergency lighting equipment must be listed for this category as determined by NEC Art. 700, Emergency Systems, and NFPA 101, Code for Safety to Life from Fire in Buildings and Structures. These codes dictate that all emergency lighting systems undergo periodic maintenance that’s recorded and kept on file.
Under UL Standard 924, battery-powered equipment must meet performance-testing requirements to ensure it can provide a specific amount of illumination for 90 min during a power outage. The UL Listing report indicates a specific battery to use within a unit, and this information is included with the system in the form of markings. If you substitute any other battery type in one of these systems, you’ll not only negate its UL Listing, but you could also damage the internal circuitry and cause premature battery failure.
Uninterruptible power supplies (UPS) can operate incandescent, magnetic, and electronic ballasts that serve fluorescent, high-power compact fluorescent, and HID lamps. A continuously operating inverter with a zero transfer time makes it possible for this type of battery inverter system to ensure the supply of emergency power to standard HID lamps. However, not all UPS systems function properly with HID ballast loading. The UPS manufacturer should be informed of the loading and should guarantee compatibility. Some complete systems are available, with a manufacturer supplying both the battery system and the ballasts. You need to recognize that these systems typically limit the type and wattage of HID lamp that can be used.
Battery-powered inverters convert DC battery power to AC power, which is then supplied to the lamp through a ferroresonant transformer. Available in single and 3-phase models, these inverter systems have different transfer time ratings to handle all types of lamps and applications.
Most lighting fixtures with integral battery/inverters specifically designed for emergency lighting duty fall into the category of unit-type equipment. Compact unit-type, battery-powered light heads are available in a variety of modes for commercial, institutional, and industrial environments. These power units have built-in test equipment or procedures that regularly exercise the fixture to ensure proper operation. If the lamps fail to successfully complete a test, a trouble light will activate. Accessories for unit equipment include a vandal-resistant plastic shield, protective wire guard, and mounting shelf.
A light head’s degree of rotation is important because it can give the user more flexibility in the configuration to illuminate the desired area during an emergency situation.
One model of unit-type, battery-powered light heads designed for stairwell/corridor egress lighting combines a self-powered full-size exit sign with two emergency lighting heads—some local codes require three heads—thereby eliminating the need for separate emergency lighting units in many applications.
One manufacturer’s emergency light features an approved Class 3a laser option. Designed for classrooms, dormitories, hospitals, nursing homes, hotels, and other commercial facilities, the laser provides visibility in smoky environments far superior to that of other lamps. It’s specifically designed to assist in the fast evacuation of a large number of people because it can provide a 40-foot beam that’s easily visible in dense smoke.
Gen-set systems. Engine gen-sets are reliable and capable of supplying emergency power to a lighting system for an extended time period. However, the biggest obstacle to wider adoption has been their inability to transfer power instantaneously from the normal to emergency source. Gen-sets generally require as much as 10 seconds to reach rated operating speed and deliver a consistent voltage or current sine wave. While incandescent and fluorescent lamp systems can run off of a gen-set power source, the inability to deliver instantaneous power usually rules out the use of standard high-intensity discharge (HID) lamps on such an emergency system. The arc of an HID lamp extinguishes if power is withdrawn for even a few microseconds, and it takes several minutes for the arc tube to cool down before arc restrike can be initiated.
Interruptible AC power systems, with a transfer time of 20 milliseconds or more from normal to emergency power and back to normal power, are suitable for use with incandescent and fluorescent lighting loads. In this case, an incandescent lamp load will resume operation as soon as power is restored; a fluorescent lamp load served by rapid-start ballasts resumes operation about 1 or 2 seconds after power is restored. Typically, this type of unit offers programmable self-diagnostic testing for 5 minutes monthly and 90 minutes annually.
Lighting industry manufacturers are working on products that would make it possible to rely on gen-set power for HID lamps. Fast transfer AC power systems with a transfer time rating of 2 milliseconds to 8 milliseconds, make gen-set power suitable for use with incandescent and fluorescent lighting loads, and some HID sources. At least one manufacturer offers a battery inverter system with a 2-millisecond transfer time, an important requirement for serving any type of HID lamp. Compatibility with several manufacturers’ HID lamps is generally recommended when specifying a specific inverter system.
One manufacturer recently developed a tool for overcoming the transfer time altogether. The HID backup device acts as a bridge between the gen-set and 175W and 250W metal halide (MH) lamps in indoor-rated fixtures, serving as an alternative to a UPS. The device powers the HID lamp until the gen-set can kick in. Installed near the ballast, the module allows the MH lamp to serve as an emergency light source when its branch circuit is part of an emergency lighting circuit connected to a standby generator. The module can provide supplemental AC power within about 2 milliseconds in the event of an AC voltage sag, thus preventing the lamp arc from extinguishing. And in the case of a complete power loss, the module can deliver power to the lamp (about 20% to 30% of its wattage rating) for as long as 2 minutes, or until AC power is restored and stable. The unit, which is mounted to the fixture assembly, is currently available for probe-start lamps.
If you can’t get the gen-set to power-up more quickly, another option is to design lights that can cope with the longer switching time.
Instant-restrike MH lamp. Typically used at sports stadiums and arenas, instant re-strike MH lamps have a lumen output and rated life similar to a standard MH lamp. Rated from 175W to 1,650W, these single-ended lamps have an external wire lead opposite the socket that connects to a pulse generator, which must be within 12 inches to 15 inches of the lamp. The pulse generator, in turn, is wired to an igniter, which is installed adjacent to the ballast. Because the pulse generator produces a high voltage, a fixture using this lamp must have a safety-interlocked door enclosing the lamp compartment. Full light output is attained immediately if the power interruption doesn’t exceed 10 seconds.
Double arc tube HPS lamp. These lamps have two arc tubes connected in parallel—only one is ignited when the lamp is first energized. If a power interruption extinguishes this arc, the second arc tube strikes instantly when the power is re-established. About 3% to 5% of full light output is immediately restored, with 90% of full output occurring within 2 minutes. If the power interruption doesn’t exceed 35 seconds. When a second power interruption occurs, such as the transfer back to normal power, the cooler of the two arc tubes will re-strike.
Auxiliary TH lamp. These lamps include a separately wired and circuited tungsten halogen (TH) lamp and socket installed within the HID lamp compartment. The circuit feeding the TH lamp is energized when normal power is lost. A time delay following return to normal power keeps the tungsten lamp energized during the time the HID lamp cools down and restrikes.
Thanks to the differing capabilities of battery-powered and gen-set emergency lighting systems, you previously had to decide upfront whether you wanted to get longevity or instantaneous operation from your system. Now, however, lighting manufacturers are blurring the lines between the two groups, offering lighting system designers more options for any situation that may arise.