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

Full sun is 2000 µmol/m2/s, supplemental lighting provides ~ 150 µmol/m2/s Light units: µmol/m2/s versus /m2 Daily light integral (DLI)

DLI (mol/m2/) = [[µmol/m2/s]/1000000] x 60 s/min x 60 min/h x photoperiod in h

100 µmol/m2/s of light for 8 give 2.88 mol/m2/day Daily light integral (DLI)

8 Field 7 Growth chamber

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Growth chamber maintained at 800 µmol/m2/s PAR vs PPFD

• PAR is photosynthetically active radiation (400- 700 nm)

• PPFD is photosynthetic photon (µmol/m2/s)

Common mistake in literature: plants were grown at 200 µmol/m2/s of PAR 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/) 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

• Light quality refers to the relative proportion of photons received at each wave 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 • /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

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LED Plants are adapted to sun light

Sun spectrum

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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