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Do you have enough light inside your greenhouse or indoor grow?With the shortest days of the year upon those of us in the Northern Hemisphere, which means a scarce six hours of daylight at Heliospectra’s plant research lab in Gothenburg, Sweden, they’re focused on how to make the sun shine…even when the sun is not.
Optimizing light in your greenhouse or CEA facility generally equates to happy plants and reliably large yields. Though any grower knows this intuitively, being able to quantify and control specific aspects of light takes the guesswork out of providing plants with what they need. There are very real operational and economic gains to be realized by delivering the appropriate amount of light at the right time.
To do this, Heliospectra tracks daily and seasonal variations in light intensity, spectral distribution, and photoperiod. Their aim is to equip growers with a lighting strategy that you can apply at any latitude, at any time of year.
These aspects of light are constantly shifting throughout each day and are dictated by the sun’s angle, your location, and time of year.
Light is dynamic
“When researchers go to the lab, they tend to use static light—turn them on in the morning, turn them off at night,” explains Heliospectra R&D Engineer Johan Lindqvist. “This is not how plants grow in the wild. Cultivators understand the need to design a system and lighting strategy that replicate both light intensity and spectral composition to mimic natural conditions.“
If you have lights in your greenhouse or indoor CEA facility already, then you may be using the on/off or “time clock” method that Johan describes.
If so, what determines your run times, and can you say with certainty that this is the most economical option for your plants and electricity usage?
Whether you go by feel, use sophisticated light-sensing equipment, or are just beginning to consider supplemental lighting for your operation, the goal of this blog series is to explore how you stand to benefit from daily light integral or DLI.
Attention to DLI = Thriving Plants
You may be familiar with DLI, which is the amount of sunlight in the range of photosynthetically active radiation (PAR) that falls to earth over a 24-hour period. DLI can be expressed as moles of light, per square meter, per day, and is often shortened to moles per day. Worldwide, DLI typically ranges from 5-60 mol m-2 d-1.
Every crop thrives at its own target DLI at each stage of its development, and values can differ even amongst varieties of a single crop. Plants receiving optimal light root quickly, develop thick stems, and branch and flower plentifully. On the low end, bedding plants and perennials tend to do well with about 3-12 mol m-2 d-1, while very high light crops such as tomatoes appreciate upwards of 22-30 mol m-2 d-1.
DLI is the sum of all light throughout the day, i.e. dependent on the Light quantity (varying intensity) and the Light duration (hours). Image Credit: Erik Runkle, Professor / Floriculture Extension Specialist, Michigan State University
Even if you live much closer to the equator than the northern latitude of Heliospectra and our plant lab in Sweden, DLI levels in your greenhouse may be below optimal levels.
While the sun may be shining where you are, once you place a house of glass between your plants and the sun, you’ve reduced the DLI between 40% and 70%. Many other factors, including glazing, shading, and clouds, can also reduce DLI.
Sample DLI based on simulations of high light area in Mexico, comparing spring natural sunlight levels with winter natural sunlight levels.
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Publication date: 12/19/2016
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