Millions of exit signs installed in the United States may not produce sufficient brightness to be visible during emergency conditions. This is a key conclusion of an exit sign field study published in January 2022 and conducted by the Light and Health Research Center (LHRC) at the Icahn School of Medicine at Mount Sinai in New York.
An estimated 42 million exit signs are operating in the United States, based on a 2008 Department of Energy estimate adjusted for a 1.5% growth. About 90% of these signs are estimated to be installed in commercial and 10% in industrial spaces.
This application served as an early adopter of LED technology, which offered advantages including higher efficiency, longer life and more. By 2005, technological development and market adoption had reached a level that the Energy Policy Act of 2005 established a maximum power of 5W per illuminated exit sign face, essentially requiring LED sources.
A differentiating characteristic of LED technology is its failure mode, which can be expressed as catastrophic (the LEDs stop producing light) or lumen depreciation (light output declines until the luminaire is no longer considered useful). Where maintaining light levels is critical for safety or productivity, light levels should be monitored and the luminaires replaced if they decline below a target threshold. Similarly, should the brightness of an exit sign significantly decline, it may be on but have unsatisfactory visibility in emergency conditions.
Many facility managers are likely not aware of the difference. Current standards require a minimum design brightness for new signs and language stating that brightness can decline over time. In some jurisdictions, life safety codes may require that signs be inspected monthly to ensure they are on, though the most recent version of NFPA’s Life Safety Code eliminated this requirement.
This resulted in a hypothesis that a substantial portion of older exit signs are operational but no longer producing satisfactory brightness to be visible in emergency conditions (see “Where’s the Way Out?” in ELECTRICAL CONTRACTOR, January 2021). The LHRC put this to the test in a field study sponsored by Colorado Lighting Inc. and the interNational Association of Lighting Management Companies, with funding by the Jim H. McClung Lighting Research Foundation.
The Life Safety Code requires exit signs be visible and legible in clear conditions from a minimum distance of 100 feet. While light level (illuminance) is important for general lighting, as it enables vision in an illuminated space, with exit signs, brightness (luminance) is key. Based on research and an early Energy Star specification, the LHRC selected an average luminance of 15 candela (cd) per square meter (sqm) as a desirable minimum metric, which theoretically would allow the sign to be visible at a critical distance of 20 feet or less in smoky conditions.
Laboratory testing of a sample of new red and green stencil-type exit signs revealed luminances ranging from 83–97 cd/sqm. The LHRC next developed a procedure for testing sign luminance in the field, measuring a sampling of points on the face’s stencil legend and performing a calculation to eliminate the impact of ambient light falling on the sign. Overall, they tested 132 red stencil-face exit signs in commercial buildings in Albany, N.Y., while Colorado Lighting tested 217 green exit signs in various Colorado buildings for a total of 349.
Nearly 25% exhibited average adjusted luminances on the legend below 15 cd/sqm, with another 10% being between 15–20 cd/sqm. The red signs fared better than the green ones, which may have been a function of relative age, LED type or operating environment. Unfortunately, the researchers could not determine the age of each sign to plot luminance.
Overall, however, a substantial portion of installed signs did not achieve the threshold of 15 cd/sqm, which presents the undesirable situation of an owner paying energy costs to satisfy the code, but not fulfilling the code’s intent for safety. If this sign population represents the overall installed base in the United States, this could cost millions.
The LHRC outlined a number of potential solutions. Additional research could be undertaken to confirm the results, expand the tested population geographically and determine date of installation to plot failure against operating age. New exit signs could be developed that either maintain a constant output (and then overdrive at end of life to produce catastrophic failure) or dynamically monitor output and either deactivate or produce an alarm that the unit is no longer producing the desirable output. Standards could be amended to require field testing of a sampling of signs. Owners could enact testing programs on their own based on manufacturer-published service life projections. Also, industry organizations could produce education to expand awareness and best practices including recommended field testing procedures.
Check out the study at http://tinyurl.com/ExitSign2021.