2019 ASHS Annual Conference

In 2017 a 3-story greenhouse in Wyoming became the site of a year-long light monitoring study. The operation began production of lettuce (Lactuca sativa L.) and tomatoes (Solanum lycopersicum L.) in spring 2016. Working with faculty and students at the University of Wyoming and Colorado State University, greenhouse management and investors provided funding for a year-long project to monitor light levels in the greenhouse. We purchased six Li-Cor LI-1500 data loggers and 12 Li-Cor LI-190R quantum sensors, two for each data logger, in fall 2017. One data logger with sensors was installed on the upper third floor of the greenhouse in each of the two tomato-growing sections. One sensor was placed near the south side glass in each section while the other was placed on top of an environmental control box on the north wall of each section. The other four data loggers and sensor combinations were placed on individual moving carousels on the middle second floor of the greenhouse. These data loggers and sensors were placed on troughs where lettuce plants would normally be growing. The logger was placed in the middle of one trough on each carousel while the two quantum sensors were placed about 3 feet away on either side of the data logger. We were thus able to quantify the light plants were receiving as they moved on each of the four carousels. Data were logged at 15-minute intervals and daily light integrals (DLI) were calculated. Data were downloaded once every 4 to 6 weeks for one year, from 14 January 2018 to 11 January 2019. Light data collected indicated that in none of the six locations did DLI reach recommended levels for either tomatoes or lettuce. Part of the reason is the tomato floor has glass on the roof and south side, but the east and west walls are solid, although painted white. This limits early morning sun and late afternoon sun in both sections. The carousels, being on the middle second floor, only get direct sun when plants are on the south vertical plane of each carousel. The rest of the circuit they do get some LED and HID supplemental light, but they are insufficient. Recommendations include increasing the number of LED bars at various locations within the carousels’ circuits.