By Norma Frank
A 2021 field study by the Light and Health Research Center (LHRC) suggests potentially millions of installed exit signs may not produce sufficient brightness to be visible during emergency conditions, due to LED lumen depreciation. This alarming problem can be addressed with code-making, product development, maintenance best practices, owner education and additional research.
The study began in 2020 with a simple hypothesis: Swift market adoption of LED technology for exit signs accelerated with passage of the Energy Policy Act of 2005. This legislation established a maximum power of 5 watts per illuminated sign face, essentially requiring LED sources, of which exit signs were an early adopter.
A key aspect of lighting maintenance is when to replace an installed product, which in turn requires an understanding of its failure mode. Traditional exit sign sources generally failed due to catastrophic failure, producing a clear visible signal of failure as the sign no longer produced light. LED, however, adds another failure mode, which is lumen depreciation. This is problematic, as the owner sees a lighting product that is operational—producing light—but may not be producing enough brightness to satisfy the design intent.
In many general lighting applications, this is undesirable but may not produce a safety risk. In others, such as exit signs, whose sole purpose is safety, the risk can become significant.
Unfortunately, often, the owner is likely not aware of the difference. As a result, exit signs are typically operated until catastrophic failure. Life/Safety codes may require periodic inspections to ensure exit signs are illuminated, but the most recent version of the National Fire Protection Association’s Life/Safety 101 Code eliminated even this requirement. Current standards require a minimum design brightness for new signs and language stating that brightness can decline over time, but currently, based on LHRC’s literature review, no standards or codes require owners to routinely inspect installed exit signage for brightness.
Based on the above understanding, a simple hypothesis was made that a substantial portion of installed exit signs are no longer producing sufficient brightness to be visible during emergency (smoky) conditions, due to age.
The LHRC at the Icahn School of Medicine at Mount Sinai put the hypothesis to the test in a field study conducted in 2021. Funded by the McClung Lighting Research Foundation, it was sponsored by Colorado Lighting, Inc. and the interNational Association of Lighting Management Companies (NALMCO).
Headed by John D. Bullough, program director, Population Health Science and Policy, the LHRC effort reviewed metrics for minimum exit brightness. The Life/Safety Code requires exit signs be visible and legible in clear conditions from a minimum distance of 100 ft. Looking at this and an early Energy Star specification, the LHRC selected an average luminance of 15 candela (cd) per sq meter, which theoretically would allow the sign to be visible at a critical distance of 20 ft or less in smoky conditions.
Acquiring a sample of new red and green stencil-type exits, the LHRC conducted laboratory photometric testing and found luminances ranging from 83 to 97 cd per sq meter. The LHRC next developed a procedure for testing luminance in the field, which involved measuring at various points on the illuminated stencil legend and then performing a calculation to remove the impact of ambient light falling on the sign’s face.
The LHRC tested 132 red stencil-face exit signs installed in commercial buildings in Albany, NY. My firm, Colorado Lighting, Inc., tested 217 green stencil-face exit signs installed in various buildings in the state. Among these 349 signs, nearly 25% showed average adjusted luminances below 15 cd per sq meter. Another 10% had declined to 15 to 20 cd per sq meter.
On average, the red signs had higher luminances than the green signs, which may have been due to a number of factors, such as age, LED type and operating environment. For example, while the LHRC tested signs in office buildings, Colorado Lighting tested signs in a variety of applications that included non-conditioned spaces such as warehouses.
Overall, a quarter of the tested signs satisfied the condition of being operational but not its intended design purpose of being optimally visible in emergency conditions.
What’s the solution? More than 42 million exit signs are estimated to be in operation in the U.S. based on a 2008 Department of Energy estimate adjusted for 1.5% annual growth in the installed base. If the LHRC results were to be considered projectable to the overall population, millions of exit signs are consuming energy and imposing an ongoing owner cost but not fulfilling their safety purpose.
A number of potential solutions are possible:
Research. Additional research could not only confirm the results but expand the tested population geographically, with greater detail such as sign age.
Product development. Exit sign products could be developed that maintain a constant light output via dimming, saving energy during operating life and then overdriving the unit at end of life to produce catastrophic failure. Alternately, the exit sign could dynamically monitor output and then either deactivate the unit or produce an alarm indicating it is time for replacement. Both technologies are available for general lighting and could be beneficial for exit signs.
Best practices. LED lighting introduced a new failure mode. Wherever maintaining light levels is critical for safety or productivity, levels should be monitored as part of a maintenance program. When levels fall below the target threshold considered minimum for safety, productivity or other required purpose, the luminaire should be replaced. Exit signs are no different.
Unfortunately, when conducting the study, we could not determine the age of each sign, and therefore we could not plot luminance as a function of sign age. This would have been very helpful information for determining ideal inspection and likely replacement points. Further research, if conducted, may help us reach this goal. In its absence, we can simply access the life expectancy published by the manufacturer, information that should be available on the catalog sheet. Or test signs in an older building and use it as a baseline for future testing.
The resulting burden on the owner would not be onerous. It would involve field testing of a sampling of exit signs at various points in life using a replicable procedure adopted from the one the LHRC used. Ideally, it would be included as part of a general monitoring program across all lighting in the application.
Codes. The Life/Safety Code once required routine inspection of exit signs to ensure they were On, based on the catastrophic failure mode of traditional lamps. The Code should change to require inspection of luminance in recognition of the lumen depreciation failure mode of LED sources.
Education. Industry organizations should support education of owners to expand awareness and maintenance best practices.
This study began with a simple hypothesis based on LED technology introducing a new failure mode to exit signs, a lighting application that is critical to human life and safety during emergencies. It demonstrated that a substantial portion of older exit signs may not be producing sufficient brightness to justify continued operation and expense. This is obviously alarming in its implications.
Fortunately, research produced an understanding of the problem so that it can be addressed. It is now up to the lighting industry and safety organizations to take action, which I strongly encourage. To download the study, visit http://tinyurl.com/ExitSign2021.