AbstractSome aspects of the metrology of fluorescence are reviewed. ASTM Committee E‐12 on Appearance has written two documentary standards on the instrumental measurement of fluorescent colors. Test Method E 1247 provides two procedures for detecting small amounts of fluorescence that might affect the measurement or use of nominally nonfluorescent materials. Practice E 991 deals with the measurement of specimens meant to be viewed under standard natural daylight, and that, therefore, must be illuminated by a good instrument daylight simulator. Two procedures are given for assessing the suitability of the simulator, and the required instrument geometry is specified. A future ASTM standard is under consideration that would describe methods for correcting the data obtained with another instrument source to the data that would have been obtained with standard daylight illumination. Two groups of standard specifications exist for fluorescent colors used for signaling or safety enhancement. One defines suitable chromaticities for both red and orange colors [among others], but ignores the fact that these colors cannot always be obtained with good lightfastness by use of existing pigments. the other group provides instead a red‐orange specification for which specimens with good lightfastness can be obtained. the relative merits of the two groups are discussed.