We present a comparison between the methods used by two regulatory standards to estimate the luminance decay time for photoluminescent safety signs and safety way guidance systems (SWGS). One of these standards is the international ISO 16069. The other is the Spanish regulatory standard UNE 23035-1. Both standards define the luminance decay time as the time for the luminance emitted by the photoluminescent sample to reach 0.3 mcd/m(2) after the excitation light over the sample is removed. Due to the fact that decay time can be really long, they propose methods to estimate it by extrapolation. The points suggested by each standard to adjust the luminance decay time curve are quite different and so are the results obtained with them. To compare both methods, four different photoluminescent safety signs were tested using the methods provided by these two regulatory standards. The samples were illuminated for 5 min with a xenon-arc source of light; luminance measurements after illumination were made with a B-510 LMT photometer, for an interval of time according to methods explained by the standards. The results were compared with real measurements of luminance decay time for each sample, allowing the luminance value to reach 0.3 mcd/m(2). Results obtained from the extrapolating methods provided by each standard showed that standard ISO 16069 was much more accurate than UNE 23035-1, which showed important deviations from real decay time values. (C) 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 383-389, 2011; Published online 7 October 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.20631