Identifies the factors that influence variability in lighting performance and gives recommendations on how such variability may be contained within tolerable limits in the specification, calculation and measurement of interior and exterior lighting systems. Provides advice on the comparison of calculated/measured values of lighting parameters with specified or target values, taking into account the uncertainties of calculation/measurement. Sets out typical uncertainties that might be expected for various elements of lighting calculations/measurements, together with total uncertainties for the overall design.