DOES THE LIGHTING TIME INFLUENCE YIELD OF WINTER GROWN SWEET PEPPER AND TOMATO?

The extremly low natural light level is the major limiting factor for winter glasshouse production in Iceland. Therefore, supplementary lighting is essential to maintain year-round production. The energy costs could be decreased by lighting during the cheaper night tariff as well as during whole weekends. The objective of the study was to test whether decreasing energy costs by lighting at cheaper times will result in satisfactory yields. Sweet pepper (Capsicum annuum L. ‘Ferrari’, 9 stems/m² and ‘Viper’, 6 stems/m²) and tomatoes (Lycopersicon esculentum Mill. ‘Encore’, 2.5 plants/m²) were grown in two growth cabinets under high-pressure vapour sodium lamps for a maximum of 18 hours light. During the period of high electrical costs for time dependent tariffs one cabinet got supplemental light during the night and during the whole weekend, whereas during the other months it was uniformly provided from 04-22 h as in the other cabinet. Temperature was kept at 24-25/17-20°C (day/night) for sweet pepper and at 22-23/18-19°C (day/night) for tomatoes. When sweet pepper received light during nights and weekends marketable yield was 5-10% lower compared to the normal lighting time. However, when normal lighting time had been restored, the yield continuously approached the yield of the traditional lighting time. In contrast, accumulated marketable yield of tomatoes that received light during nights and weekends did not approach the yield obtained at normal lighting time with final yields amounting to about 15% less yield. From an economic viewpoint it is recommended to provide light at normal times.