This paper describes the relation between measurement instrumentation characteristics and the accuracy of photometric measurements of typical retroreflective materials in a photometric range. A review of the fundamental geometric and photometric terms used in the photometry of retroreflectors is presented to form a basis for discussion. The measurement method described is the method which involves determining a ratio of retroreflected light to incident light. Test instrumentation used in this measure-ment is described in terms of photometric linearity, spectral response and geometry. The instrumentation characteristics are then related to the geometric and spectral characteristics of the retroreflected light patterns from typical retroreflectors. Highly resolved observation angle curves are used to analyze errors relating to source/receptor aperture size. Entrance angle curves of various retroreflectors are used to determine goniometer accuracy requirements. The effects of rotation angle and presentation angle are illustrated by measurements on typical retroreflectors. Retroreflected spectral data is used to determine spectral fit of the photoreceptor. Effects of variability in source color temperature are presented. Instrument requirements for varying degrees of accuracy are then stated in terms of the spectral and geometric characteristics of the retroreflector to be tested.