Updated daily light integral (DLI) maps now available

New DLI maps have been created from an updated database that includes data from 1998 to 2009.

Daily light integral (DLI) is the amount of photosynthetically active radiation (PAR) received each day as a function of light intensity and duration. DLI maps display the ambient light delivered daily during each month across the entire United States. The original maps released in 2002 were researched and developed by Jim Faust at Clemson University and Joanne Logan at the University of Tennessee.

These researchers developed a series of monthly DLI maps to provide a tool for horticulturists to estimate the potential growth and flowering responses for various plants throughout the year. At least 40 research articles studying plant responses to DLI have been published since the original DLI maps were released. Most of this research focused on greenhouse ornamental production.

The original DLI maps were based on solar radiation data from 239 sites recorded from 1961 to 1990. New maps were created from an updated database that included data from 1998 to 2009. This updated information provides higher resolution data modeled from satellite images of cloud cover. The new maps provide more geographically precise data reflecting recent weather patterns.