Compare emergency illumination systems for life safety

Emergency illumination insights

• Various methods exist for emergency illumination in commercial facilities, with adherence to codes like NFPA 101 being crucial.
• Batteries are favored when project requirements do not dictate otherwise.
• Centralized systems are cost-effective for large projects, while unit batteries suit smaller ones; aesthetics and performance also influence choice, necessitating early consideration to avoid rework.

There are many methods available to energize emergency illumination for egress in a commercial facility. Regardless of the source of power, the primary codes one must be familiar with and adhere to are NFPA 101: Life Safety Code, International Building Code, NFPA 70: National Electrical Code and additional source dependent NFPA standards. When other project requirements such as fire pumps, elevators or owner preferences do not steer the source of power decision-making, batteries are an attractive option.

According to NFPA 101, Section 7.8.2.1, there are three common and reliable forms of battery topology used in emergency lighting applications: general-purpose light fixtures with battery backup, a centralized battery inverter system and unit equipment with self-contained batteries.

For general-purpose light fixtures with battery backup, specific light fixtures within a space are designated as emergency fixtures. An emergency LED driver with an integral battery will be provided for each designated fixture. When normal power is lost, the designated fixtures are provided with backup power from the battery and will remain on.

A centralized inverter is similar in function, yet there will be a larger localized battery providing power to many designated light fixtures, similar in topology to a standby generator.

Unit equipment is different in that they are additional fixtures provided for the sole purpose of emergency illumination and do not provide any general lighting per NFPA 101 Section 7.8.2.2. They have self-contained batteries within their housing and are known colloquially as bug-eyes.

Emergency illumination cost

Cost is a common driver in the emergency illumination decision-making process for the owner. A cost analysis shows a centralized battery inverter system makes more economic sense on large-scale projects with high fixture counts, where integration with advanced lighting controls is needed and where low yearly testing/maintenance cost is desired.

Labor rates play a bigger role when specifying a centralized system due to emergency lighting branch circuits being separate from general lighting branch circuits from source to load per NFPA 70 Section 700.17. Unit batteries are a better bang for your buck on smaller projects including renovations, addition or new construction with low fixture counts, where labor costs are high. The cost for general lighting with battery backup typically lands snug between these two for Day One costs.

Lifetime cost of ownership for emergency illumination would include routine testing, maintenance and replacement of batteries. These costs accumulate for a large facility with emergency batteries distributed throughout a building and should be weighed against the larger Day One costs of a central system.

Emergency lighting aesthetics

Emergency lighting does not quite fit into the architectural formula of aesthetic lighting design. Their expectation is that they will have to choose between a bad or a worse option. A centralized system is the more aesthetic option as it is likely to be hidden behind the doors of an electrical closet. Thermoplastic unit equipment is not likely to clash with the visual appeal of most maintenance facilities, but would likely stick out in a premium or minimalist architectural space (see Figure 1).

Figure 1: Wall-mounted unit battery equipment. Courtesy: SHP

There are options for concealed unit equipment that are recessed and hidden behind what looks like an access panel and drop down to present themselves when normal power is lost. General lighting provided with backup batteries blend into the space, but the same is not true of their associated relay test buttons (see Figure 2).

Figure 2: Test button and LED indicator provided for the adjacent general-purpose downlight fixture with battery backup. Courtesy: SHP

This small single-gang sized device with a test button and LED indicator is only a potential problem for premium and minimalist architectural spaces. Typical emergency illumination manufacturer specifications allow for these test switches to be as far as 50 feet away from the light, which may allow for careful consideration in placement if necessary.

Performance of emergency illumination systems

Despite all operating on batteries, these systems can perform differently while still meeting the minimum time requirement of 1.5 hours (see NFPA 101 Section 7.9.2.1). Knowing the difference is key to designing a code-compliant system. The centralized battery system provides full rated output for the entirety of the 90 minutes.

The biggest performance weakness of a centralized system is in its name, it is a single point of failure. Unit batteries can present a challenge when balancing the maximum-to-minimum ratio of 40:1, according to NFPA 101 Section 7.9.2.1.3.

When general-purpose light fixtures with battery backup are specified, one must keep in mind the reduced lumen output when powered from the battery. A standard 2×4 troffer provided in a 12-foot ceiling may be specified at 4,800 lumens. A standard 10- or 14-watt battery pack provided for backup would provide something close to half the normal lumen output. This reduction is critical to keep in mind when performing photometric analysis for emergency egress illumination. Additionally, its lumen output declines throughout the 90-minute period that it is fed from the battery. While a degradation in lumen output is allowed within the code (NFPA 101 Section 7.9.2.1.2), it is something to be aware of. There are both high wattage and constant output battery pack options available, but they come at a price.

Emergency illumination limitations

One potential limitation for a centralized system is space. If the goal is to use a central inverter on a smaller project, it may be difficult to find wall or floor space for the unit. Due to it being stored in a conditioned space, it does not suffer from the same limitations as the two other options that are located out where the lighting is located (see Figure 3).

Figure 3: An installed emergency lighting inverter. Courtesy: SHP

One limitation that engineers must be kept in mind in colder climates is the temperature rating. This rating is important to be mindful of when providing exterior emergency lighting and designing with battery drivers or self-contained batteries outside. The standard low-end threshold is 32°F.

One common method for providing emergency battery backup to an exterior wall-mounted light is to locate the battery on the opposite side of the wall inside the building. A cold weather battery pack can be specified when batteries must be located outside and the temperature is a concern, but these can be pricy (see Figure 4).

Figure 4: Exterior rated unit battery supplied lighting. Batteries are located on the interior of the building. Courtesy: SHP

In addition to the temperature, other environmental factors one would want to keep in mind when specifying outdoor unit equipment and batteries would be wet, damp or hazardous environments.

Maintenance and testing

Maintenance and testing of emergency illumination systems can be a tedious task to perform for trained personnel or staff totaling many hours for larger buildings. One benefit of a centralized inverter is that all the equipment is in a single location and should be easily accessible. The testing and reporting can be an automatic feature of the system to not require any true procedure to be performed per NFPA 101 Section 7.9.3.3.

Maintenance on the other hand, typically requires more specialized skills and is not something a commercial building’s maintenance staff is often qualified to repair. Emergency drivers with battery backup provided for general-purpose light fixtures and unit equipment with self-contained batteries share many of the same benefits and downsides.

With both being distributed, the total quantity of devices to test and perform maintenance on can be overwhelming. The most budget-friendly options require a button to be pressed to indicate a status (NFPA 101 Section 7.9.3.1.1). The self-test feature is available with most battery units that will continuously display battery and light fixture status with an LED, automatically performing the NFPA required testing as outlined in NFPA 101 Section 7.9.3.1.2. This alleviates the need to be within hands reach of the light fixture for testing.

Laser pointers are a common optional feature that allow for emergency illumination system testing from a distance. Testing and reporting for general-purpose lighting with battery backup can be simplified with automatic testing and reporting by specifying driver capable of remote testing and reporting via Bluetooth. Maintenance in buildings with different fixture types and many different types of batteries can be intensive. The use of general lighting with battery backup in large spaces with tall ceilings may require tools beyond a standard ladder for maintenance and testing.

The three common battery backup options are all effective when specified correctly. The best option will depend on the requirements of the project and the needs of the client. It is recommended to review these considerations early in the design process to avoid any potential rework.

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