Energy efficiency of greenhouse cucumber production under LED and HPS lighting

The response of cucumber crops to supplemental lighting with high pressure sodium (HPS) and LED lights and their effect on energy use efficiency of lighting and heating were studied. In three compartments, area 50 m², three lighting systems were employed: top light LED-interlight LED (LED-LED), top HPS-interlight LED (HPS-LED), top HPS-interlight HPS (HPS-HPS). The respective electrical powers of the top lights and the interlights on experimental plots were 128-64, 180-64, and 180-56 W m^-2. In summer, over 67 harvest days, mean daily yields were about 0.54 kg m^-2, the same in all compartments. Electricity consumptions were 4.4, 5.6 and 5.5 kg kWh kg^-1 of cucumber, for LED-LED, HPS-LED and HPS-HPS, respectively. LED-LED differed statistically from the others. Heat consumptions were estimated at 1.3, 0.7 and 0.5 kWh kg^-1. In winter, from November to mid-March, over 99 days, mean daily yields were 0.49, 0.62 and 0.57 kg m^-2. Yield accumulation in mid-winter, when solar light was scarce, started slower under LED-LED than under other lighting systems. The electricity consumptions for LED-LED, HPS-LED and HPS-HPS were 9.0, 9.9 and 10.9 kWh kg^-1, with HPS-HPS statistically differing from the others. Estimated heat consumptions were 8.4, 4.0 and 3.6 kWh kg^-1. The employed LED lighting increased electricity use efficiency by about 20% both in summer and winter. However, because of the lower heat output from pure LED lighting was compensated in winter by much heating directed to developing fruits and yield was low in mid-winter, heating per unit yield rose high under LED-LED.