Once the dread of architects, you can now incorporate emergency lighting fixtures into an innovative design without sacrificing performance.

Thanks to manufacturers of emergency lighting, you don't have to put up with obtrusive and ugly fixtures anymore. That's because they're now designing emergency lighting with aesthetics in mind. In fact, some fixtures are completely invisible. Sound interesting? Read on. Depending on the application and facility, certain types are preferable. Here's what you have to choose from:

• Special designer-type fixtures. You can use these where a completely unobtrusive appearance is of paramount importance. Fitted with an extruded aluminum frame and an acrylic or polycarbonate lens, some models come in full recessed, semi-recessed, and surface-mounted versions. One manufacturer uses a "push the lens" procedure to test proper operation. This unit design is ideal for any interior space where you (or the architect) want to avoid the appearance of emergency lighting equipment. Another interesting variation is the design conceals the fixture and lamp behind a door until activated, as shown in the diagram (above). These virtually invisible compact lighting fixtures preserve the integrity of an architectural or interior design while meeting national and state code requirements. Served by a central battery system, they are available in either ceiling or wall-mounted models.

• Fluorescent emergency ballast. The fluorescent ballast/battery pack converts a standard fluorescent fixture into an emergency light. The unit serves the same linear lamp as the fixture, so there's no exposed equipment to detract from the ceiling appearance. (Some use a separate compact fluorescent lamp as the emergency light source inside the fixture.) Some battery units can operate two or three 32W (4ft) T8 fluorescent lamps, two or three 39W, or two 40W to 55W (4-pin) long compact fluorescent lamps. This emergency fluorescent ballast unit is useful in commercial offices and public buildings, institutional, and health care facilities.

Most are available as dual-voltage models. You can retrofit them in the field or order them as part of the fluorescent fixture for new installations.

Here's how they work. When AC power returns after a power outage, the emergency ballast automatically switches to the charging mode and fully recharges in 24 hrs. You can check the unit for proper operation with a test switch. However, the newest emergency ballasts take some of the hassle out of Code-required testing. Instead of standing on ladders or using an extension device to hold the test switch, you simply use a handheld remote control transmitter to operate the emergency ballast, verifying its operation. You can install an emergency ballast unit inside the ballast channel, on top of the fixture, or remote from the fixture. This inconspicuous positioning inhibits unauthorized tampering and reduces the risk of vandalism. Heat can affect battery operation, so make sure you use units rated for operation at elevated temperatures.

A special version of this type of ballast serves as an uninterruptible interim lighting unit for generator-powered emergency lighting systems. During power failures, auxiliary generators typically take up to 10 sec. to reach speed and generate emergency power. This emergency ballast unit provides high illumination between the time AC power is lost and the emergency generator starts providing power for lighting. The unit operates one 17W to 32W T8, one 20W to 40W T10 or T12, or one 18W to 55W (4-pin) compact fluorescent lamp at high illumination for a minimum of 5 min. It is ideal for hospitals, educational facilities, and industrial plants.

• Unit-type equipment. Compact unit-type battery powered lights (usually using reflector type lamps) are available in fairly unobtrusive models for commercial and institutional environments. They're ideal for schools, hospitals, and offices.

Fitted with LED indicator lights, their design accommodates suspended T-bar ceilings and usually offers four head styles and several battery options. You can mount the battery/charger remotely. Industrial units and explosion-proof versions for special rated applications are also available.

A special version of the unit is the perfect solution to stairwell/corridor egress lighting. This series 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 light units in many applications.

Generally, power units for emergency lighting systems have built-in test equipment, or procedures, that regularly exercise the unit to ensure proper operation. Failure to successfully complete a test will activate a trouble light. Accessories for unit equipment include a vandal-resistant plastic shield, protective wire guard, and mounting shelf. The battery source can be lead calcium, pure lead, or nickel cadmium.

A vandal-resistant "always on" emergency lighting unit, using one or two compact fluorescent lamps with a polycarbonate diffuser, is a natural choice for apartment house hallways, stairwells, and exit locations.

• HID backup lighting. The NEC requires emergency lighting to back up slow-restrike high intensity discharge (HID) systems. The long restrike time for high pressure sodium (HPS), and even longer time for metal halide (M-H) sources, requires some form of back-up lighting system that's immediately available when power returns. HID sources need from 5 to 15 min. to cool down and restrike after power is lost.

You can specify an industrial HID lighting system to include a tungsten halogen lamp as a backup source within some of the fixtures. Here, you would provide a separate power supply for the tungsten lamp, which usually operates at 120VAC, allowing you to connect it to an emergency generator circuit.

Whenever the unit senses a loss of lamp current, the tungsten source turns on. A time delay following return to normal power keeps the tungsten lamp energized during the HID restrike time.

• Exit lights. Exit light design keeps evolving. Today, compact fluorescent, light emitting diode, and cold cathode light sources are popular. In addition, retrofit LED and compact fluorescent kits are available to convert older exit lights to longer life, lower wattage units.

Many compact fluorescent lamp/ballasts may have a power factor rating of 50% or less. As such, you should use the volt-ampere (VA) rating instead of the wattage rating when doing calculations. This way, you won't overload the circuits serving the equipment.

Many LED exit signs operate on less than 5W per face, whereas the older incandescent lamp models may consume 20W to 40W per face. Manufacturers offer a full line of Energy Star compliant exit signs, using the LED source. Developed by the U.S. Environmental Protection Agency (EPA), the Energy Star program promotes the most energy-efficient exit lights on the market today. Although they have a higher initial cost than other sources, Energy Star signs have much lower power consumption as well as lower maintenance costs.

Sidebar: Summary of Emergency Lighting Requirements

Safety requires installed emergency lighting throughout the path of any egress, stairs, aisles, corridors, ramps, escalators, and passageways leading to safety. You must continually illuminate these locations for a minimum of 90 min. For codes requiring longer illumination times, many manufacturers offer UL-listed modes with 2- and 4-hr extended run times.

Transfer of emergency lighting must be automatic, within 10 sec. of the loss of normal lighting power. The emergency lighting unit must provide initial illumination that's no less than an average of 1 footcandle (fc), or 10 lux, and a minimum at any point of 0.1 fc, or 1lux measured along the path of egress at floor level.

The design should not exceed a maximum-to-minimum illumination uniformity ratio of 40 to 1. Adhering to this ratio minimizes dark-to-bright spots. In addition, you must clearly mark any changes in direction or routes.

If you select a battery source of power for the 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 Underwriters Laboratories (UL) listed as Life Safety Equipment. Therefore, they have very stringent requirements in their construction and performance. Thus, 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 state when, where, and how to use the equipment. They also dictate that all emergency lighting systems have periodic maintenance, with records kept on file of this maintenance.

Under UL Standard 924, battery powered equipment must meet performance testing requirements, since it must 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 negate its UL listing. Besides, a substitute battery could damage the internal circuitry and cause premature battery failure.

Sidebar: Emergency Lighting Pointers

Lighting the egress path. When specifying emergency lighting for egress paths, visibility of the space is the most important consideration. For more uniform lighting, you may need more sources of lower output light rather than a fewer number of higher output devices spaced more widely.

Areas such as small offices not other otherwise requiring emergency light and normally occupied by five or more people, should have lighting at the door that's equal to the adjacent egress route.

Location of exit lights. Exit lights are, or can be, an integral part of the rest of the emergency lighting system. They should direct occupants to the nearest exit and clearly indicate clearly where that exit is. You must use the word "EXIT" and directional arrows.

Mounting heights (to the bottom of the fixture) are usually between 6.5 ft and 7.5 ft above the floor. You typically mount these above an exit door. During emergencies involving fire and smoke, however, it may be necessary for occupants to crawl along the floor. In fact, some state codes now require the use of low level satellite signs located near the floor. NFPA standards state when low-level exit signs are required, you must place them not less than 6 in. but not more than 8 in. above the floor. NFPA also has specifications for fixture size and letter size of these satellite signs.

Most design considerations for emergency lighting are Code-related. In general, federal, state, and local codes spell out what you need for reliable and sufficient emergency lighting as part of the conditions for a Certificate of Occupancy.