Effects of LED Interlighting on Plant Growth, Fruit Yield, Quality, and Energy Use Efficiency in Greenhouse Mini-cucumber Production
Two experiments were conducted in 6 greenhouse compartments during winter 2011-12. Experiment one evaluated single LED inter-lighting module per twin-row (36.7µmol/m2/s) without or with top HPS lamps (hanged above the crop canopy, 165µmol/m2/s just above the plant head). To determine if high plant density (canopy coverage) can improve the response to LED inter-lighting, 2 plant densities (2.8 and 3.6 plants/m2) were used in the experiment. Experiment two evaluated two LED inter-lighting modules (73.4 µmol/m2/s) per twin-row without or with top HPS lamps (120 µmol/m2/s).
LED interlighting improved fruit colour, number, weight and size. The LED interlighting allowed a higher percentage of light emitted by the light sources reached the canopy and had a higher light use efficiency than the top HPS calculated based on total light output from the light sources. However, the light use efficiency was similar when calculated based on the light reached the canopy. Therefore, the LED interlighting increased light use efficiency mostly by increasing the light reaching the canopy when compared to top HPS. Higher plant density improved the response of mini-cucumbers to LED interlighting and further increased light use efficiency, and the response to LED interlighting appeared to be slightly better under lower top HPS lighting (120 µmol/m2/s). Therefore, the response of mini-cucumbers to LED interlighting can be optimized by using proper crop management and top/interlight ratio. The LED interlighting module achieved higher energy use efficiency than the top HPS in both experiments.
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