2014 ASHS Annual Conference

Year round greenhouse vegetable production with artificial lighting in northern regions is capital and energy intensive. To be successful, the lighting system and crop management must be optimized to maximize light and energy use efficiency. Interlighting, applying the supplemental light within crop canopy, could improve light distribution and interception within canopy and thus increase crop yield and light use efficiency. However, the high bulb temperature with the standard HPS (high pressure sodium lamps) has prevented its use as interlighting in the popular twin-row greenhouse vegetable cultivation system (with small row width). Light emitting diodes (LEDs) have low bulb temperature, making it a good light system for interlighting. Therefore, this study was conducted to evaluate the effects of GreenPower LED inter-lighting module (114W, 220 µmol output, 2.47 m long) recently developed by Philips on plant growth, fruit yield and quality, and light 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.