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Photoluminescent Exit Signs

Posted By Gregory Steinman, Monday, September 01, 2003
Updated: Thursday, February 14, 2013

Photoluminescent signs are no longer considered supplementary means of egress for today’s buildings; they are relied upon as the main means of egress lighting in the form of exit signs. Photoluminescent signs are glow-in-the-dark products that rely on an external light source for "charging.”

Performance

Photoluminescent signs can now be listed according to UL 924, The Standard for Emergency Lighting and Power Equipment. These products are included in the category (FWBX) Self Luminous and Photoluminescent Exit Signs. Although these products can comply with UL 924, they cannot be considered or treated the same as electrically powered signs.

Photoluminescent exit signs in the market today will not comply with the minimum illuminance values required by UL 924. These products have been listed using an observation visibility test comprised of two observers, ranging in ages from 18-30, 31-40, 41-50, and 51-70, for each test. This test includes allowing five minutes for each observer to acclimate his or her eyes to the ambient light conditions. This subjective test has been in the UL standard for many years. In today’s world, we must constantly review product standards for applicability and maintenance. In a terrorist attack on a building, are there five minutes available for occupants to adjust their eyes to begin planning their escape?

Previous Life Safety Code requirements included a minimum luminance value for exit signs. This minimum luminance value was 0.06 foot-lamberts (0.21 candela/square meter). The latest publication of the Life Safety Code dropped these product requirements and deferred these to product standard UL 924. The removal from installation codes of product specific construction requirements has been the practice lately. It is normally a good practice to avoid requirements in an installation code that cannot be inspected, but the performance of different technologies can vary tremendously. Recently, the National Electrical Manufacturers Association published a white paper titled "Exit Sign Brightness for Visibility and Safety.” 1 This paper included luminance performance for different exit sign technologies, including photoluminescent and LED. The results concluded that a typical LED type sign is approximately 1,000 times as bright as a photoluminescent type sign. The difference is even greater at 90 minutes into the test. This document can be obtained atwww.nema.org. Prior to September 11, 2001, I would have never thought about this test being relevant in the real world. When would someone need 90 minutes to escape a building? Obviously, when someone was near the top of the World Trade Center, all of this time was needed to get down the thousands of stairs to safety.

National Fire Protection Association Standard 101 Life Safety Code2 requires these signs to be continually illuminated while the building is occupied. It typically takes sixty minutes for these signs to become charged prior to being able to meet the observation visibility test in UL 924. Upon the opening of a business, the photoluminescent sign is discharged. For the first sixty minutes of building occupancy, the means of egress are suspect. The sign that is intended to protect the occupants is not ready to perform for the first hour of charging. What will happen to the building occupants should an emergency occur in the first hour of occupancy?

NFPA 101 requires a photoluminescent exit sign to be illuminated on its face in accordance with its listing. The typical illumination requirement for these type signs is a prescribed footcandle level of fluorescent lighting. Ceiling grid type luminaires are normally relied upon for charging these signs. Upon installation, this level can be verified rather easily with a light meter. Unfortunately, the initial lighting levels are not maintained over the life of the lamps in the charging luminaire. As the lamp ages, the lumen output level becomes lower, normally referred to as lumen depreciation. The charging lighting level available months after the installation will not be as good as the level available upon initial installation. Electrical exit signs must be energized for a fixed period of time prior to the laboratory testing to allow for lumen depreciation. Since that charging luminaire was never evaluated for this purpose, will the building occupants be aware of the need for lumen maintenance for the charging source luminaire?

Inspection

NFPA 101 requires photoluminescent exit signs to be illuminated by a reliable light source as determined by the authority having jurisdiction. The word "reliable” is not defined by NFPA 101; therefore, this may have varying degrees of definition by varying authorities. The Code does not require any identification for the reliable light source, leaving the building occupants ignorant of the importance of the light source that is needed for charging the photoluminescent exit sign. One will not find switches on the branch circuits powering electrically powered exit signs. There will definitely be switches on the branch circuits powering the reliable light source. Since there is no identification on the reliable light source or branch-circuit switch, what would happen if the building occupants turn off the charging luminaire when not in that specific building area? If this area were the means of egress, this escape route marking would be compromised.

In many buildings, these switches are occupancy sensors. These sensors would ensure the photoluminescent sign is illuminated while the building is occupied, but if the occupancy is sporadic, the sign may never reach its charging time of sixty minutes.

The decision by the authority having jurisdiction to determine light source reliability is extremely difficult. When a testing laboratory issues a listing for a luminaire, there is no evaluation for reliability or performance. Electrical shock and fire hazards are the only evaluations performed on that luminaire. Lumen maintenance and life testing are not part of a luminaire product listing evaluation. Power quality will also impact the reliability of the charging luminaire. UL 924 requires a voltage surge test on electrically powered exit signs. This test is not performed on luminaires intended to charge the photoluminescent exit sign. How can the authority having jurisdiction determine a light source is reliable when the nationally recognized testing agency that issued the product listing for that light source does not even address these issues?

Energy Efficiency?

One of the best features of photoluminescent signs is they do not directly use electricity; but the charging luminaire that is required will use electricity. Most installations of photoluminescent exit signs rely on already existing luminaires so that the electricity is not an additional load for the facility. But, one must consider the typical sixty minutes charging time required for these signs.

The United States Department of Energy manages an energy efficiency program called Energy Star. Many different products, such as computers, household appliances and emergency exit signs, can be labeled as energy star compliant if the product meets the requirements of the program. Emergency exit signs must use less than five watts per face to meet the existing Energy Star requirements.3

Let’s do the math: a typical photoluminescent exit sign must be charged for one hour prior to being able to perform its function. The normal fluorescent ceiling grid type luminaire includes four lamps, each rated 32 watts. Not including the watts losses in the ballast, this results in 0.128 kW hours. This is only the amount of energy required to initially charge the photoluminescent exit sign. That luminaire must remain on at all times while the building is occupied. An Energy Star electrically powered exit sign uses 5 watts maximum. For a 24-hour period, that results in only 0.12 kW hours.

Conclusion

Claims that photoluminescent emergency exit signs are easy to install, require no maintenance, and use no electricity are simply not true. The installation requires an installer to use a light meter to verify the illumination level is in accordance with the product listing. The charging light source must be determined reliable and the lumen levels monitored. The electricity used to charge the photoluminescent sign for one hour can exceed the energy consumed by an electrically powered sign for 24 hours. Photoluminescent exit signs are not a simple answer to a life safety issue. These signs require engineering review and constant maintenance.

1 NEMA LSD-13-2001 Exit Sign Brightness For Visibility and Safety

2 NFPA 101-2000 Life Safety Code

3 Energy Star Program Requirements for Exit Signs Partner Commitments


Read more by Gregory Steinman

Tags:  Featured  September-October 2003 

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