ASHS 2024 Conference

The adoption of supplemental lighting in horticulture has allowed greenhouse growers to increase the yield of multiple crops by at least 10%, with a 300% yield increase documented for cucumbers when transitioning from unlit to lit production. Since then, horticultural lighting has advanced significantly to now include dynamic LED lighting, which provides unparalleled control over the light intensity, spectrum and zoning within the greenhouse. This has allowed greenhouse growers to further maximize crop productivity, but also to target improvements in crop quality and to diversify their production. For example, the greenhouse industry has seen the introduction of multiple berry crops, leafy crops, Asian cucumbers, etc. in recent years, all of which have varying lighting requirements ranging from 12 to 25 mol of light per square meter per day. The ideal spectrum also differs between crops, as do the light saturation points and target intensities. Beyond enhancing photosynthesis and increasing crop productivity, dynamic LED lighting can also be used to improve the nutritional quality and taste of various crops through spectral adjustments during the growth cycle. In a trial comparing the impact of broad and narrow spectra on basil, a broad spectrum produced a flavor profile stronger in eucalyptol whereas a narrow spectrum produced an estragole-dominant crop. This resulted in a milder flavor under a broad spectrum and a stronger flavor under a narrow spectrum. With dynamic lighting, growers can adjust the spectrum to target different flavors and thus different markets. Further, the application of high levels of blue light during the last week of production has been repeatedly shown to enhance the antioxidant capacity of red leafy greens through the bioaccumulation of anthocyanin. The Brix, or sweetness, of fruiting crops has also been improved under dynamic lighting, with commercial trials showing a minimum of 7% increase in Brix in speciality cherry tomatoes compared to fixed spectrum lighting. This increase could potentially be enhanced with end-of-day (EOD) light treatments, which early trials have suggested to enhance the translocation of sugars from leaves to fruit. As such, dynamic LED lighting can improve both the productivity and nutritional quality of greenhouse crops, allowing forward-thinking growers to meet the growing population’s needs in terms of both quality and quantity.