MSU Extension Floriculture & Greenhouse Crop Production

These maps provide the average outdoor daily light integral throughout the continental United States and were developed by Jim Faust at Clemson Univ. To estimate the average DLI in your greenhouse, determine the percentage of light transmission that reaches your crops. For example, if you measure 6,300 footcandles outside the greenhouse and an average value of 4,100 footcandles inside, your light transmission value is about 65% (0.65).  Multiply the DLI value on the maps by the light transmission value to get the estimated DLI inside your greenhouse.