Yujin Park, currently a third-year Ph.D. student at Michigan State University, delivered this oral presentation during the 8th International Symposium of Light in Horticulture held in East Lansing, MI in May, 2016. She investigated the use of adding far-red radiation in the production of ornamental seedlings grown under sole-source lighting.

Watch the entire presentation here:


By Yujin Park and Erik Runkle

A combination of red (R; 600 to 700 nm) and blue (B; 400 to 500 nm) light-emitting diodes (LEDs) is commonly used in sole-source lighting of plants grown in highly controlled environments. R and far-red radiation (FR; 700 to 800 nm) regulate photomorphogenesis, including stem elongation and leaf expansion, and to some extent, photosynthesis. However, little research has been published on how FR LEDs can be used to improve plant growth and quality attributes during seedling production. We grew seedlings of snapdragon (Antirrhinum majus) at 20°C under six sole-source LED treatments with an 18-h photoperiod. All treatments included 32 µmol m-2 s-1 of B radiation (peak = 451 nm) and different intensities (subscript in µmol m-2 s-1) from R (peak = 660 nm) and FR (peak = 729 nm) LEDs: R128, R128+FR16, R128+FR32, R128+FR64, R96+FR32, and R64+FR64. Plant height and total leaf area linearly increased as the R:FR or the estimated phytochrome photoequilibrium of each treatment decreased. Shoot dry weight was similar under the same total photon flux (400 to 800 nm) even when R radiation was partially substituted with FR (considered minimally photosynthetic) and linearly increased when R was constant and FR increased. Photosynthetic efficiency (PE), which is calculated as shoot dry weight per unit leaf area, was correlated positively with the calculated yield photon flux of each +FR treatment. In addition, PE linearly decreased as the amount of R was increasingly substituted with FR radiation. We conclude that supplementation of FR to R and B radiation can increase PE and subsequent dry mass accumulation without excessive leaf and stem expansion.

The published paper of this study is here.

Adding far-red radiation benefits ornamental seedlings