The aim of the current research was to analyse the effect of four water irrigation treatments (1·20, 1·00, 0·80 and 0·60 of the crop water requirement) on the relationships among leaf area index (LAI), radiation use efficiency (RUE) and green canopy cover in a potato crop (Solanum tuberosum L.) cv. Agria. The crop was established in a commercial plot irrigated with a centre pivot system in Southeast Spain during the 2011 and 2012 seasons. In both seasons, the highest light absorption efficiency values occurred at the LAI value of 3 that corresponded to maximum ground cover. With regard to the irrigation treatment, a significant linear response was indicated for RUE. The results indicate that the 1·00 irrigation treatment produced the best result, improving water resources management without reducing crop yield.