Dual-technology exit signs eliminate battery backup

Dual-technology exit signs with light-emitting diodes (LED) and photoluminescence (PL) deliver reliable, maintenance-free operation for decades.
Photo courtesy Isolite

by Bill Lynch

For building owners and managers striving to meet fire and safety codes, “dual-technology” exit signs that combine the efficiency of light-emitting diode (LED) lighting with new photoluminescent (PL) materials can help increase reliability and performance over decades of use.

This hybrid approach combines two established exit sign technologies in a single unit. During normal power conditions, the sign is illuminated with highly efficient LEDs. When the power goes out, a translucent exit stencil diffusor made of photoluminescent material provides the illumination. This is charged by the LEDs while electric power is provided to the sign.

Egress marking requirements often dictate the installation of exit signs in locations with low-light conditions. This problem, coupled with energy conservation strategies such as occupancy sensors, can make it impossible to use traditional PL signs and achieve code compliance. Recognizing this problem, some emergency lighting manufacturers now offer advanced, dual-technology options utilizing internal LEDs to “charge” the photoluminescent material, rather than relying on an external source.

This ensures the exit sign’s visibility, no matter the power conditions. The increased reliability of this dual technology also has a significant side benefit—it eliminates the need for battery backup, reducing some of the costs related to testing, maintaining, or replacing exit signage over time.

The dual technology approach eliminates the need for backup power for the exit sign, whether through an internal battery or an external inverter/generator. This significantly increases reliability, simplifies maintenance, and reduces total costs.

The battery problem

Traditionally, exit signs include internal batteries to power the product in case of power outage, yet batteries remain the highest point of failure in these systems. Batteries typically have a lifespan of five to seven years before they must be replaced, and less when damaged by corrosion and overheating.

Exit signs must meet a number of standards from regulatory agencies. This includes, most notably, the National Fire Protection Association (NFPA) 101, Life Safety Code—which requires a reliable source of light and at least 90 minutes of emergency light if the building’s power goes out—and Underwriters Laboratories (UL) 924, Standard for Safety of Emergency Lighting and Power Equipment.

To meet these code requirements, signage with backup batteries must be tested every 30 days, a practice that typically involves sending a maintenance worker to climb a ladder and push a small button to confirm the batteries are still in working order.

In reality, these guidelines are not always followed. So if the battery fails, it is often not known until an actual power outage. If the sign fails to illuminate fully, or at all, when it is most needed, it could constitute a major life safety issue and even potential liability.

Photoluminescent signs

Standard photoluminescent exit signs have been in use for more than a decade. However, as a standalone technology, this has limitations.

For example, such signs require an activating light source to shine on them during all times of building occupancy. Often the available light is not sufficient to charge the photoluminescent material, particularly as energy efficient building standards such as California’s Title 24 lead to lights being dimmed or switched off more frequently when not in use.

When insufficient light is available, photoluminescent signs fail to illuminate to the required standards and could pose a serious safety hazard.

Better in combination

The hybrid approach combines technologies to provide even more reliable illumination, whether the power is on or off. However, designing such units turned out to be far more complex than simply putting both in a single architectural fixture.

One design approach utilizes internal LEDs to charge the PL material to ensure it is visible at all times at a 30-m (100-ft) viewing distance for a minimum of 90 minutes—the normal standard for electric signs.

Since there is no battery to check on a monthly basis, these types of units cost less to maintain and are expected to perform for 20 or more years. Many come with Occupational Safety and Health Administration (OSHA), NFPA 101, NFPA 70, National Electric Code (NEC), and UL 924 approvals.

Special LEDs emit the specific wavelength of light required to optimally charge the photoluminescent material so it provides the proper illumination to meet code requirements.

Cost savings

There are other benefits to this hybrid approach as well, which costs only nominally more than traditional LED signage.

The typical battery-reliant LED exit signs use about 4 watts of power whereas the hybrid unit consumes about half the power—less than 2 watts. This is due to a unique electronic driver circuit providing current control and protection, which helps ensure optimal LED efficiency and life.

Eliminating a reliance on batteries is also good for the environment, since both the manufacture and disposal of batteries involves toxic chemicals.

While LED technology has improved to the point where it can last more than 20 years, battery technology has not always kept pace. It can be the weak point in exit sign reliability and maintenance. Hybrid LED/photoluminescent technology eliminates this liability and provides a more reliable operation for decades.

Bill Lynch is president of Isolite, an independent emergency lighting manufacturer. Lynch graduated with a bachelor’s degree from Bowdoin College in 1977. In 2001, he became a member of the Underwriters Laboratories (UL) Standards Technical Panel for UL 924, Standard for Safety of Emergency Lighting and Power Equipment. He can be contacted at blynch@isolite.com.

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2 comments on “Dual-technology exit signs eliminate battery backup”

  1. I like that you said normally the LEDs light up but, when the power is cut off, a diffuser of photoluminescent material provides illumination. I think that these signs are really important because you don’t need the power to have them functioning. I’m grateful for your information about how dual technology eliminates the need for backup power for the sign and reduces total costs.

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