Light-Emitting Diodes as Supplemental Lighting in Viticulture Field Research

A light-emitting diode (LED) system was evaluated as a tool for field research to investigate light effects on grapevines. Preliminary laboratory trials were conducted to develop response curves for photosynthetically active radiation (PAR) and temperature as a function of distance from the LED light source. LED panels were subsequently deployed in a three-year field study of three light-exposure treatments on developing fruit clusters of Vitis vinifera cv. Cabernet Sauvignon: 1) clusters exposed to direct sunlight, 2) clusters shaded by the canopy, and 3) canopy-shaded clusters exposed to supplemental LED light. Laboratory trials and vineyard field studies demonstrated that LED panels could provide supplemental light to grapevines over a broad range of PAR, up to and exceeding the photosynthetic light saturation point for exterior leaves, by adjusting the distance of the LED panel to the target. Although bench trials indicated significant convective heat close to the LED panel, field studies detected few temperature differences among cluster treatments. Varying results were primarily attributed to temperature measurement locations related to experimental objectives; bench trials measured target surface temperature, but field studies monitored whole cluster temperature. LED panels were effectively deployed to provide supplemental light to shaded grape clusters without significantly altering cluster temperature.