Abstract
Lettuce growth data are presented that show the importance of the daily light integral for predictable vegetative growth. Dry mass accumulation is shown to be proportional to the light integral, and a consistent daily light integral is proposed to be central to consistent production. Supplemental lighting control rules are defined and described and a computer implementation is used in conjunction with ten years of hourly weather data to test (by simulation) adequacy of the rules to control supplemental lights and movable shades in greenhouses to achieve a consistent daily integral of Photosynthetically Active Radiation (PAR), mol-m –2 -day –1 , on days of either insufficient or excess solar irradiation, which are most days. The rules require neither historical data bases of weather characteristics nor daily weather forecasts. Control decisions are suggested to be made hourly, based on the current day’s accumulating solar PAR integral inside the greenhouse. The model is sensitive to time-of-day electricity rates, changing seasons, weather, greenhouse and component characteristics, and greenhouse location (latitude and longitude). The rules contain parameters with values suggested for northeastern United States solar conditions but which may be adjusted for local solar climates that are significantly different.
Published Version
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