College of Agriculture, Forestry and Life Sciences; Public Service and Agriculture; Research

New national light maps help greenhouse growers manage plant growth


CLEMSON – Horticulturists across the United States can use new light management tools to ensure greenhouse plants receive the correct amount of light needed for proper growth.

Daily light integral maps
Daily light integral maps can be used to ensure greenhouse plants receive the correct amount of light needed for growth.

The U.S. Daily Light Integral Maps developed by Jim Faust, a Clemson horticulture associate professor, and Joanne Logan, a University of Tennessee biosystems engineering and soil science associate professor, allow growers to better manage light their plants receive.

“For example, a grower can estimate the number of days per year supplemental lighting may be necessary to achieve the desired plant growth during winter months or how much shade cloth may be required to reduce the light intensity delivered to crops during the summer months,” said Faust, who is leading the project.

Often, natural sunlight is enough to help plants grow, but sometimes supplemental lighting is required, especially in areas where cloud cover during winter months does not provide plants with enough light for photosynthesis. The new maps might be able to help growers lower costs by allowing them to reduce the amount of supplemental lighting and shade cloth required to grow healthy plants.

The scientists created a map for each month for each state, including Alaska and Hawaii. Data for the maps were collected using a satellite radiation model developed by the National Renewable Energy Laboratory. This model uses data to estimate how much light an area receives each hour. These maps provide high-resolution data for about every 38 square miles and can be used to determine the amount of supplemental lighting plants require.

This is not the first time daily light integral maps have been used. The original maps were published by Faust and Logan in 2002. When the first maps came out, the daily light integral concept was not widely used by professional horticulturists. But, with affordable sensors, Cooperative Extension Service outreach efforts, educational materials and programs, professional horticulturists have accepted the daily light integral concept and are now commonly using it, Faust said.

“Today, growers frequently reference daily light integral measurements when talking about environmental conditions and plant responses to those environments,” Faust said. “This knowledge has contributed to improved management of the light environment in the commercial production of a wide range of horticultural crops.”

Greenhouses are major contributors to the United States economy. A study by the University of Florida Institute of Food and Agricultural Sciences shows nursery and greenhouse production generate about $200 billion annually. Called the “green industry,” products grown in greenhouses include flowers, bedding plants, tropical foliage, as well as vegetables.

To learn more, visit the Daily Light Integral Maps interactive map at

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