In commercial greenhouses or grow rooms, several strategies can be used to help properly manage light levels throughout the day and seasonally. Some of the primary reasons why greenhouses manipulate light levels include temperature and irrigation management, photoperiod control, minimizing crop stress, and optimizing photosynthesis.
The DLI fixtures can increase the light intensity a crop receives and improve and accelerate its growth and development. Retractable shade curtains and whitewash can reduce and scatter light intensity to create a more desirable growing environment during high-light periods.
What Is Light and Why Is It Important?
Light is a form of energy called electromagnetic radiation. Electromagnetic radiation, whether from the sun or supplemental light solutions varies in duration (energy over time), quality (wavelength or color), and intensity (the amount of light at each wavelength or color). Increasing energy in the PAR range increases plant photosynthesis, (the plant’s most basic metabolic process). Each crop species has an optimal light intensity that maximizes photosynthesis and plant growth. When there is not enough light, growth and crop quality can decline; and if there is excessive light, photosynthesis and growth will not increase despite the expense of keeping the lights on.
Horticultural researchers measure instantaneous light in micromoles per square meter per second, or μmol/m2s of PAR. This “quantum” unit quantifies the number of photons (individual particles of energy) used in photosynthesis that fall on a square meter (10.8 square feet) every second. This unit provides an instantaneous light intensity at the time the reading is taken. Natural light levels however are continuously changing and a single measurement in time does not accurately represent the amount of light a plant has received in a day.
Daily light integral (DLI) is the amount of PAR received each day as a function of light intensity (instantaneous light: μmol/m2s) and duration (day). It is expressed as moles of light per square meter per day, or: mol/m2d. DLI measures the total amount of PAR received in a day. Dutch Lighting Innovations can calculate this for any crop in any grow-situation in any part of the world.
Under light-limiting conditions (such as during the winter or when growing in growrooms), most greenhouse crops benefit from supplemental lighting. But remember, supplemental lighting is generally worthwhile only when increased photosynthesis leads to greater revenue (such as more turns of plugs, cutting liners or more cut flowers).
The Dutch Lighting Innovations Horticulture researchers can provide more information about DLI and can advise on layouts and the Dailiy Light Integral for greenhouses worldwide with all variety of flowers or plants.
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