UL 924 Exit Sign Code Requirements

Exit signs are the most common building signs in the world. And due to their safety role, they are also the most regulated signs. There are several codes that make requirements of an exit sign. For example, the International Fire Code (IFC), International Building Code (IBC), National Fire Protection Association’s (NFPA) Life Safety Code, OSHA (Occupational Safety and Health Administration) standards, and Underwriters Laboratories Code 924 (UL 924) all address the performance and design specs of exit signage. Below, we look at critical UL 924 exit sign code requirements for photoluminescent (a.k.a. luminescent) exit signage.

UL 924 requirements for photoluminescent exit signage

UL standard 924 applies to exit signage, emergency lighting, and power equipment that (a) operates on less than 600 volts of electricity and (b) illuminates/powers critical areas or equipment during power outages. UL 924 establishes several criteria for a photoluminescent exit signage. Below are its criteria for the use and installation, external illumination, design characteristics, and testing of photoluminescent signage.

Use and installation

In terms of mounting location, UL 924 recognizes two types of exit signs: signs mounted in proximity to the ceiling, and signs mounted in proximity to the floor. In the latter case, only signs marked with wording that indicates their appropriateness for floor proximity should be mounted near the floor.

Signs may be placed near the floor to remain visible in the event of thick smoke, with some floor-mounted signs mounted as little as six inches above the finished floor (requirements can vary by municipality). However, ceiling proximity signs should be mounted no less than 80 inches above the finished floor in accordance with NFPA 101.

External illumination

When luminescent signage is required to have more than 1-foot candle (1 ft-c) of illumination on its surface, it is marked to indicate a 5 ft-c requirement. If it requires a certain type of illumination source, this is marked as well.

NFPA and UL 924 exit sign code regulations require that luminescent signage burn with a minimum luminance of 0.06 feet lamberts, and that they remain visible from at least 50 feet for 90 minutes of total darkness.

Design characteristics

Unless indicated otherwise by local law, luminescent exit signs should contain letters that are (a) at least six inches high and (b) have a stroke width of 3/4 inch. The space between the letters should be 3/8 inch. If a larger than normal sign is chosen, its design characteristics must increase proportionately to ensure its legibility from a distance.


Unless a sign maker requests a sign to be tested at 50 or 75 feet, UL tests exit signage at 100 feet using a photometer. This test is officially known as the UL analytical luminance visibility test.

The Importance of UL exit sign code requirements

UL exit sign code regulations ensure that buildings are outfitted with signs that perform according to indication. At Jessup Manufacturing, we carry a variety of UL listed luminescent exit signs that offer superior illumination and burn time. If your building still contains inefficient electrical signage or environmentally hazardous Tritium signage, contact us today, and let us show you the advantages of switching to luminescent signage.

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