Common indicators used to examine the potential for utilising natural radiation of urban forms include the sky view factor (V-s), the height to width ratio and the urban horizon angle. These indicators are conveniently related to one another. In comparing simulations of sky view factor with those of simulated solar irradiation, which itself relates well to illumination, this paper tests the effectiveness of all three - based on analysis of three existing Swiss districts. From this, it is concluded that the absence of treatment of direct solar radiation, sky anisotropy or reflected radiation seriously impairs the ability of the V-s-related indicators to offer meaningful insights regarding natural radiation potential in the localised case. Predictions of annual irradiation from aggregations of V-s also perform badly, but the aggregate V-s does correlate reasonably well with irradiation so that judgements of overall radiation availability may be made with some confidence. (c) 2006 Elsevier Ltd. All rights reserved.