The insertion of climate-based daylight metrics as a requirement in several design guidelines calls for a better understanding of their effectiveness. This paper draws attention to the sensitivity of annual daylight metrics to changes in input reflectance values. The uncertainties related to the choice of guidelines and of simulation techniques were also considered. Total Annual Illumination (TAI) showed the most consistent correlation and the highest sensitivity to variations in reflectance (up to ±60% from the benchmark), independently of the geometrical characteristics of the space. Other annual metrics were less sensitive, or showed a poorer correlation. The deviations among different simulation techniques varied with the chosen metric too ( for TAI), but all techniques were equally affected by variations in reflectance. The results highlighted the importance of selecting appropriate metrics for annual climate-based daylight evaluations.