UL 924 Requirements
UL listed Exit Signs must match all code requirements which have been set forth in UL 924.
This is the standard for Exit Signs, Emergency Lighting, and Power Equipment. The majority of Exit Sign lettering used to be red. However at present time, green lettering is used quite a bit. While the specific coloring of Exit Sign lettering may be included in the local codes of a City or State, the UL 924 listing has no specific code requirements. Red and Green Exit Sign Lettering are both code compliant and in accordance with UL Code.
Exit Sign Letters must be a least six inches high. The width of the stroke needs to be 3/4 inch, and the space between those letters must be 3/8 inch. If one chooses a larger Exit Sign, the Exit Sign must increase proportionally in size to assure that the Exit Sign is legible from a distance. UL 924 and NFPA 101 have specified a minimum luminance of 0.06 ft. lamberts. This industry standard was put in place in the 1970s. Test that reflect viewing distance of Exit Signs are based on a viewing distance of 100ft. The 100ft. viewing distance requirement was established by NFPA 101. There are two tests that are conducted to determine compliance with the 100ft viewing distance. These two tests are conducted within UL 924. The first is the UL analytical luminance visibility test. This is done with a photometer and a 100ft. observation visibility test. This is the standard, but there is and exception to the rule. This exception allows manufacturers to request a testing distance of 50 feet, 75 feet, or 100 feet. Once this test is completed, UL mandates that these Exit Signs be marked with the legible viewing distance.
Self-Luminous Exit Signs are continuously powered by a self contained source of energy. UL requires a date of replacement to be legible on the exit sign. This is mostly for the Tritium Exit Sign. These signs use a radioactive gas that does expire. Photoluminescent Exit Signs need exposure to ambient light to properly charge. These exit signs are required to have a constant source of ambient light and are in fact UL listed. UL recommends floor proximity and egress markings for safety. These pathway marking systems are set to be installed in low level locations on walls floors and low level areas. UL approved photoluminescent materials may be examined for their suitability. UL listing has put in place to insure your safety and the safety of others.