IMPROVING SWEET PEPPER PRODUCTIVITY BY LED INTERLIGHTING

Light-emitting diodes (LEDs) have recently emerged as a potentially energy-efficient technology in horticultural lighting, and their low heat generation favors their use between the stems of sweet pepper (Capsicum annuum L.) trained to two-stem plants. We studied the effects of LEDs (57 W m^-2), installed between the stems without top lighting, on fruit yield and quality of greenhouse-grown sweet pepper cultivar ‘Ferrari’. Plants were grown at 7.16 stems m^-2 in peat growing medium and fertigated with nutrient solution (2.5 dS m^-1). Red fruits were harvested weekly over 16 weeks. Continuous light measurements determined by the photosynthetic photon flux density (PPFD) indicated limited natural light availability inside the canopy at the level of fruit development, where no more than 5-10% of the radiation received at the top of canopy penetrated. LED interlighting considerably improved the light conditions there. The weekly marketable yields of LED-illuminated plants were equal to or greater than those from plants not receiving artificial light. LED interlighting increased the total marketable yield by 16% (LED 14.6 kg m^-2 and non-LED 12.6 kg m^-2) mainly due to the increased fruit number. Fruits of LED-illuminated plants were deeper red in color, suggesting faster fruit maturation. The cost-benefit analysis showed that the yield advantage covered the electricity costs at present values, but the overall profitability of interlighting was sensitive to the yield advantage, product pricing and installation costs.