Two tomato (Solanum lycopersicum) cultivars 'Dafnis' and 'Cluster' were grown in a high-tech glasshouse at the National Research and Development Center for sustainable agriculture (ESTIDAMAH), Riyadh, Saudis Arabia during the 2017-2018 season to evaluate the effect of supplementary light on tomato growth, yield, fruit quality and water use efficiency. Supplementary light was introduced by high-pressure sodium lamps (PAR, 210 µm01 m-2 s-1) for 6 h (12:00-6:00 am). Results reveal that supplementary light significantly increased plant height of both 'Danis' (13%) and 'Cluster' (18%) in comparison to natural light.
