How can I determine exit sign products that meet the 100 ft spacing requirement in code?
A. Signs that have been determined by UL standard 924 not to meet the 100’ viewing distance are to be labeled with their maximum viewing distance. There are two prescribed visibility testing programs for exit signs in accordance with UL 924; the analytical test method and the observation visibility test. Both tests are unique and offer different sets of criteria to determine a pass/fail but, unfortunately, there are currently no discrete markings required to determine which test method was used during qualification. The analytical test method is a highly repeatable test. In abbreviated form – A digital camera, connected to a computer, is used to test 20 specific points along the illuminated letters E X I T. These measurements are used to determine maximum and minimum values to calculate averages, max to min ratios and the like. The data is referenced to a minimum average illumination level, in this case no less than 8.57 cd/m (candelas per meter squared). The non-illuminated background
