A calibration method comprising, for each of one or more light sensors: (a) under influence of one or more substantially non-zero illumination levels in the target environment, using the light sensor to measure the sensed light level corresponding to each of these one or more illumination levels; (b) receiving a template light level value corresponding to each of the one or more illumination levels, representing the light level at a target location in the target environment substantially removed in space from the location of the light sensor, each of the one or more template light level values being assumed for the environment rather than measured by a light meter; and (c) determining a relationship between the sensed light level and the light level experienced at the target location, based on an evaluation of the one or more sensed levels relative to the one or more template light level values.