Light Quantity and Quality in Controlled Environment Agriculture Krishna Nemali, Ph.D. Light : Quantity Light is • An electromagnetic wave • Exists in both wave (with certain frequency) and particle (photons) forms Photosynthesis & Light Light units: µmol/m2/s 1 mole contains 6.022 x 1023 entities of a substance 1 micro mole is 1/1000000th of a mole 1 µmol/m2/s = 6.022 x 1017 light particles (photons) hitting a m2 area in one second Full sun is 2000 µmol/m2/s, supplemental lighting provides ~ 150 µmol/m2/s Light units: µmol/m2/s versus Watts/m2 Daily light integral (DLI) DLI (mol/m2/day) = [[µmol/m2/s]/1000000] x 60 s/min x 60 min/h x photoperiod in h 100 µmol/m2/s of light for 8 hours give 2.88 mol/m2/day Daily light integral (DLI) 8 Field 7 Growth chamber 6 /hr) 2 5 4 3 2 Integrated light light (mol/m Integrated 1 0 Growth chamber maintained at 800 µmol/m2/s PAR vs PPFD • PAR is photosynthetically active radiation (400- 700 nm) • PPFD is photosynthetic photon flux density (µmol/m2/s) Common mistake in literature: plants were grown at 200 µmol/m2/s of PAR Quantum sensors Measure PAR Supplemental lighting • Provide additional light for photosynthesis during cloudy days or winter months • Extend photoperiod • Improve crop quality • Indirect benefit of heating in winter • Can provide 100 to 400 µmol/m2/s Many options, what to choose? HPS CFL MH LED HPS MH LED CFL Comparison of different supplemental lights Lamp Light intensity Photon Cost per fixture (µmol/m2/s) at efficiency ($) 0.7 m below (µmol/joule) fixtures SE 1000W HPS 1090 1.02 275 DE 1000 W HPS 1767 1.7 600 MH (315 W) 491 1.46 640 LED (380 W) 653 1.7 1200 From Nelson and Bugbee, 2014 Light Quality • Light quantity or intensity refers to total number of photons received per unit area in a given time • Light quality refers to the relative proportion of photons received at each wave length per unit area Courtesy: Erik Runkle, Michigan State Univ. Why is light quality important? Photomorphogenesis • Blue light is important for stomatal opening and chlorophyll synthesis • R/FR ratio determines elongation in plants (shade avoidance) • Circadian rhythms in plants are influenced by light quality Sun spectrum Sun spectrum at noon on December 10, 2009 30000 25000 20000 15000 10000 Energyunit per nm per area 5000 0 400 500 600 700 800 Wavelength (nm) LED Plants are adapted to sun light Sun spectrum 30000 25000 20000 15000 10000 Energyunit per nm area per 5000 0 300 400 500 600 700 800 Wavelength (nm) http://www.flor.hrt.msu.edu/assets/Uploads/LEDs-pt2.pdf NASA.org Carotenoids compete with chlorophyll for light in the blue band .