In commercial buildings, emergency lighting control is essential for safe egress in the event of a power outage or other emergency situations. Lighting specifications that contain products which meet UL 924 requirements ensure the project has reliable and compliant emergency lights in the space, thereby meeting applicable building codes. However, space requirements vary considerably, and the resulting designs can become complex.
As technologies and products evolve, and systems change, UL will periodically revise its emergency lighting control standards, which may impact the lighting specification. For example, effective April 2022, UL 924 – the Standard for Emergency Lighting Equipment – updated its requirements for compliant products. A building’s UL 924-listed emergency lighting components must now actively monitor normal power to ensure emergency lighting is engaged within 10 seconds of power loss. This change eliminated some previously allowed methods to sense the loss of normal power, but there are still a variety of ways solutions can meet UL 924.
To simplify the specification and installation process, we’ll look at the different codes and standards associated with emergency lighting, and present four key implementation strategies ranging from standalone, code-compliant emergency fixtures to centralized emergency lighting control as part of an integrated lighting solution that can offer additional benefits that enhance system flexibility.
There are several factors to consider when planning an emergency lighting solution including controls and fixtures in the space, individual project needs, and the type of backup power used. Ultimately, the emergency solution you install must be reliable and comply with all project requirements while meeting applicable codes (such as NFPA 70, 101, and 110) to deliver these three basic functions:
- Get power to the emergency fixture during a utility power interruption.
- Force the emergency fixture to a predetermined output level (often, but not always, 100%), bypassing any controls.
- Prevent the emergency fixtures from being turned off or bypassed before normal power is restored.
The Relationship between UL Standards and Building Codes
Building inspectors require the finished building to meet the relevant building codes, such as the National Electric Code (NEC) or International Building Code (IBC). Using UL-Listed solutions is one way to meet these code requirements. However, emergency lighting systems can easily be designed to meet code requirements without each of the separate components bearing a UL 924 mark; for example, UL 1008 may be necessary in some situations. For this reason, it is better to reference the required building codes in an emergency specification rather than the specific product standard that can be used to meet them.
Four Primary Methods of Implementing Emergency Lighting Solutions
Strategy #1: Standalone Emergency Fixtures
A standalone solution uses dedicated fixtures that are always-on or turn on only upon loss of normal power. It can be deployed in three different ways:
- Dedicated emergency fixtures: Common in corridors and stairwells, these are powered by a central normal/emergency source and are on all the time. When normal power cuts out, the emergency power source (generator or inverter) takes over.
- Fixtures powered by emergency power only: These fixtures are off when normal power is present and come on with centralized emergency power only when normal power is lost.
- Integrated “bug eye” fixtures with self-contained batteries: These fixtures are for installations where no central emergency power is present. They are connected to normal power which is used to charge the batteries. When normal power is present, the fixtures are off, and the batteries are charging. When normal power drops out, the fixtures automatically turn on.
This is a simple, code-compliant, distributed strategy. The standalone fixtures are in addition to general-purpose lighting, are not controlled by a lighting control system, and may be fully illuminated even when a space is unoccupied. They offer virtually no flexibility, must be tested regularly, and batteries will eventually require maintenance or replacement.
Strategy #2: General Purpose Fixtures with Battery Backup
In this scenario, certain general-purpose fixtures are replaced with specialized emergency fixtures. These fixtures each contain an integral specialty emergency LED driver with battery. Under normal power, the battery is charged by means of a constant-hot connection to the emergency LED driver, while a separate normal (non-emergency) driver controls the LEDs. When normal power is lost the normal driver loses power and the LEDs are powered by the emergency LED driver and battery.
Emergency LED drivers are meant to provide illumination that satisfies the required footcandle levels for egress; these are typically fixed at a level below the full output capacity of the fixture. Having a battery backup in the fixtures allows use of standard-looking lighting fixtures that can be connected to a typical lighting control system. As with emergency-only fixtures, this is a distributed approach that does not enable adjustable emergency lighting levels and requires regular testing and battery maintenance (Figure 1). However, this is a viable and practical solution for applications where no central emergency power is available.
Figure 1: Emergency LED Drivers Wiring Schematic
Strategy #3: Zone-Level Automatic Load Control Relays (ALCR) and Branch Circuit Emergency Lighting Transfer Switches (BCELTS)
If the building uses a central emergency power system, ALCRs or BCELTS allow standard general-purpose fixtures to be used for emergency lighting, eliminating the need for specialized battery-backup fixtures, and allowing integrated control via a lighting control system.
ALCRs are UL 924-listed devices that provide emergency power to lighting loads by bypassing the local control device in the event of normal power loss. In normal operation, the local control dims or switches the load. When normal power is lost, the ALCR bypasses the local control and provides the load with normal/emergency power, forcing it to full and locking out the local control. This strategy does not rely on specialty emergency fixtures, but it does require the purchase and installation of an appropriate ALCR relay for each zone (Figure 2).
Figure 2: Overview of Automatic Load Control Relay (ALCR)
With certain control types, such as some ELV or phase-adaptive dimmers, the power source to the fixture must be switched completely from the control to an emergency feed rather than simply bypassing the control. In these cases, a BCELTS, which is listed to UL 1008 rather than UL 924, must be used instead of an ALCR (Figure 3).
Figure 3: Branch Circuit Emergency Lighting Transfer Switch
ALCR or BCELTS solutions require no long-term maintenance, although they are still subject to regular testing and verification. Some variations of these devices can trigger emergency lighting via a contact-closure from a third-party system, such as a Fire Alarm Control Panel (FACP). The challenge of using this strategy is that an emergency relay is required for each zone of emergency lighting, and emergency lights are forced on to 100%. These relays can add hardware cost and wiring complexity, potentially increasing the amount of time and materials that need to be installed on a project.
Strategy #4: Centralized Emergency Lighting Control
For the most flexible, cost-effective, and robust emergency lighting solution, you may be able to utilize the features of a centralized lighting control system, wherein one piece of equipment senses and activates emergency lighting for all or part of the lighting system. This is achieved using a UL 924 Listed central power-loss-sensing device that sends a contact closure signal to a compatible lighting control system. The lighting control system then forces all pre-programmed emergency lights to a pre-defined level (not necessarily 100%). Like the ALCR/BCELTS solution, this strategy requires the use of a centralized emergency power source (Figure 4).
Figure 4: Sharing the Power-Loss-Sensing Device Among Multiple Controls
A centralized emergency lighting strategy provides significant benefits. Neither dedicated emergency fixtures nor additional relays need to be installed on emergency zones. Furthermore, emergency functionality can be easily configured via software, allowing designers to potentially select which fixtures are activated during an emergency, and even what light level each emergency zone should go to. Reduced emergency light levels may allow for use of a smaller generator, while still maintaining the minimum light levels required by code.
Centralized emergency control can even be accomplished with wireless lighting control systems. With some implementations, such as the Lutron Vive system, emergency-specific, red-labeled controls are available for inspectors to easily identify emergency zones. These controls deliver the labor savings associated with wireless systems, but do not increase system cost or add complexity to the installation.
A centralized emergency solution is the most future-proof and flexible option. Little to no additional hardware (such as a single device to centrally monitor normal power) may be necessary, and a centralized solution facilitates easy adjustments to system programming over time. Software-based changes can determine how fixtures respond in an emergency power situation versus a crisis condition.
Work with Manufacturers that Make the Design Process Easier
As smart lighting control systems become more prevalent in commercial buildings, owners and tenants expect even more robust lighting performance, different sequences of operations, and a wider variety of lighting control protocols. Because there is no universal approach to emergency lighting, it’s important to take an individual approach to every project, understand the goals of the job, and be sure the emergency lighting is considered early in project discussions.
To minimize risk and maximize productivity, you’ll want to work with a manufacturer who can help answer your questions and can support the design, implementation, and installation of different control and dimming protocols to deliver the desired system performance. This includes proper selection of optimal ALCR, BCELTS, or emergency sensing equipment. Look for a provider who offers end-to-end solutions for both normal and emergency zones, and has the support, training, and technical expertise in place to make the installation as easy as possible.
