Although the sun’s spectral quality is constant, it’s highly variable in intensity, duration (daily and seasonal) and direction. Many strategies, including shading and supplemental illumination systems, have been developed to deal with the undesirable indoor production conditions associated with light fluctuation.
Sunlight conditions in greenhouses can vary rapidly, affecting temperature, humidity and luminescence. To compensate, greenhouse ventilation, heating, shading, irrigation, humidification and lighting equipment must be reasonably responsive to these fluctuations if a controlled growing environment is to be achieved. This requires precise engineering and the proper selection of equipment and control devices. It also requires an understanding of the capabilities and limitations of the greenhouse equipment systems, sensors and controllers.
Most integrated environmental control equipment can make nearly instantaneous adjustments to equipment in response to changing sensor information, predictive algorithms and programmed logic responses. In general, automated controllers are far faster at telling the equipment components what state they should be in than the equipment can respond. Even if the equipment could respond instantly it would seldom be beneficial to do so since excessive on/off cycles can limit the life of motors, switch gears and light fixtures. Properly tuned integrated climate control systems respond to changes in the environment in a dampened or attenuated fashion that strikes a balance between the need to maintain set points and the need not to overtax equipment nor overshoot the degree of response.
Control over how much light a greenhouse crop receives can be influenced by two principle methods: shading and supplementary illumination.