Enhanced sweet pepper yield through high-intensity artificial lighting and optimized plant density in high-latitude winter production

In Iceland, extremely low natural light levels during winter make greenhouse crop production largely dependent on supplemental lighting. This study evaluated the interactive effects of plant density and lighting configuration on yield and fruit quality of sweet pepper ( Capsicum annuum cv. Ferrari) under controlled cabinet conditions. Plants were cultivated at two densities under high-pressure sodium (HPS) lamps, using either top lighting (TL) alone or in combination with interlighting (IL). Under low natural light level, marketable yield tended to increase with both higher light intensity and plant density, primarily due to a greater number of fruits per unit area, while average fruit weight remained relatively stable. Under higher natural light level, the effects of plant density and lighting were minimal. The combination of TL and IL slightly increased unmarketable fruit due to blossom-end rot and light-induced damage. These results suggest that higher plant densities, when combined with adequate supplemental lighting, may enhance yield during periods of limited natural light in high-latitude greenhouses.