A stand-alone light integral controller

Control of the daily integral of Photosynthetic Photon Flux Density (PPFD, mol m(-2) day(-1)) is necessary for predictable plant growth and to meet specific crop production goals. A stand-alone light controller would greatly help both commercial growers and researchers meet this requirement in a cost-effective manner. Intelligent light control can also save money by making optimum use of off-peak electrical energy for lighting. In addition, the heat added by the supplemental lights can significantly reduced the heat demand in certain climates. A design is presented for a stand-alone light controller and computer simulation results are shown to illustrate the savings possible when taking into account electricity rate structures and the effect of thermal energy added by supplemental lighting. Electricity rate structures having low off-peak rates, as in central New York, significantly reduce supplemental lighting cost. Approximately 70% of the supplemental lighting was predicted to occur between 10 p.m. and sunrise during a typical year to reach a daily PPFD integral target of 17 mol m(-2). For climates that are cold and cloudy, such as Ithaca, NY, with a daily PPFD integral target of 17 mol m(-2), more than half the heating needed with no supplemental lighting was offset by using the lights.