A method is described for statistically analysing the relationship between weather and electricity demand for applications to practical load estimating by electricity supply engineers. The characteristics of the specific meteorological elements to which the demand has been found to respond are discussed, particularly those affecting heating and lighting demands. The thermal-lag factor appropriate to the delay in consumer response to temperature changes and the influence of the cooling power of the wind on heating load are examined. In order to assess the lighting load, observations of the atmospheric transmission of light are used to derive a method for reducing cloud and visibility forecasts to their daylight illumination equivalents.