LEDs from a Plant Scientist’s Point of View
Cary A. Mitchell
Department of Horticulture & Landscape Architecture
Purdue University
[email protected]
2012 International Meeting on Controlled Environment Agriculture
Session 1: Light in Controlled Environments
Cambridge University
Downing College
September 10, 2012
Why LEDs for Plants? (>20 years ago)
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Historical basis in the space program: Wisconsin and KSC
Plants shown to grow under red LEDs only
Plants grown under red + blue light usually do better
Solid state = robust, long lived, low mass
Waveband selectable
Massive ballast and high voltage not required
Promise to reduce ESM requirement for space life support
Much interest in LED applications for CEA
LEDs popular for plant applications because…
• photon-emitting surfaces are not hot
– waste heat is removed remote from photon emitters
• LEDs can be placed quite close to plant surfaces
• desired photon flux requires less electrical power
– inverse square law (Ι α d-2) is not a factor as for hot HID lamps
• luminous efficacy of LEDs is improving rapidly
– blue LEDS 49-50% efficient at nominal drive current
– 615-nm and 630-nm red LEDS 30% efficient at 350 mA
– 660-nm red LEDS 38% efficient at 350 mA
• potential for advances in light distribution
– system architecture, luminaires, shade avoidance, etc.
One
2007 ASHS
Workshop on
LEDs
in Horticulture
One of the most
highly read/cited
Issues in ASHS
literature
John Sager
LEDs in Plant Photobiology Research
• Replace diffraction gratings
• Less need for broad-band sources, multiple filters
– Cutoff filters, heat filters, safelights
• challenge to get LEDs with desired peak emissions
– Bin selection, custom fabrication
• Will base of emission spectrum be as narrow as desired?
– May be an issue with long irradiance times or high irradiance
responses
– Will cutoff filters have to be used with LEDs to determine
contributions of different photoreceptors?
Image courtesy of A.J. Both, Rutgers University
1.0
Blue LED
Normalized Photon Flux
0.8
Red LED
0.6
0.4
0.2
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350
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550
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650
Wavelength (nm)
700
750
800
Phytochrome photoreversible forms overlapping absorption spectra
Image courtesy of Daedre Craig and Erik Runkle, Michigan State University
Folta & Childers, 2008. HortScience 43(7): 1957-1964.
From work by Gioia Massa and Cary Mitchell, Purdue University
‘Triton’ Pepper
Overhead Lighted
Intracanopy Lighted
Plants look OK under
red + blue LEDs
But under
white light….
It is much easier to diagnose
plant health under broadspectrum white light than
under monochromatic light,
such as for these ‘Triton’
pepper plants suffering
necrosis resulting from
intumescence
Image from work of Massa and Mitchell, Purdue University
Image from work of Celina Gomez and Cary Mitchell, Purdue University
Kim, H. et al. 2006. Acta Hort. 711: 111-119.
Examples of less efficient LEDs
“White” LED = Blue LED + phosphor
<50% as efficient as the blue LED)
Screw-in LED lamp
(probably 85% as efficient as hard-wired)
Contemporary Lighting Technologies for Plants
• Light-emitting diodes - waveband selectable
• Sulphur lamps - broader band than LEDs
• Plasma lamps - broader band than LEDs
• Induction lamps - broader band than LEDs
The importance of actively heat sinking
high-output LEDs
• Critical for performance and lifespan
– Forced air for dense clusters of LEDs ≥ I watt
– Recirculating water for very high output/densities
• Makes light-emitting surfaces “touchable”
• Permits intracanopy distribution of light
– Overcomes mutual shading within foliar canopies
– Prevents premature senescence, abscission
– Enables higher photosynthetic productivity
Massa
&
Mitchell
Purdue
University
Lightsicle design by ORBITEC
Printed-Circuit LED “Light Engines”
2.5 cm
ORBITEC Light Engine
• 1 row of sixteen 440 nm blue
• 4 rows of sixteen 640 nm red
• 2 rows of ten 520 nm green
• 2 photodiodes
Intracanopy LEDs
Overhead LEDs
Close-canopy lighting saves electrical energy because of close LED placement to plants
Array design by ORBITEC
From work by Lucie Poulet and Cary Mitchell,
Purdue University
Smart LED Lighting for Major Reductions in
Power and Energy Use for Plant Lighting in Space
and for Terrestrial CEA
• “Smart” LED lighting systems could avoid lighting empty
spaces prior to canopy closure
• Automation of plant detection and LED switching would
save labor
• Smart lighting could be adapted for intracanopy (vertical)
as well as overhead (horizontal) LED lighting systems
• Smart lighting could conserve considerable energy beyond
just taking advantge of the unique properties of LEDs
Detection: How it works
Targeted lighting of widely spaced lettuce seedlings using close-canopy LED lighting
Empty spaces between plants are not lighted
LED Applications for the Greenhouse Industry
Technologies, protocols, best practices, guidelines
– For LED photoperiod lighting of ornamental crops
– To replace INC and CF lamps for night-interruption treatments
– To determine R/FR ratios for efficient flower induction/crop development
– For propagation and finishing of transplants
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Vegetable
Ornamental
End-of-day lighting
Daylength-extension (DLI) lighting
– For supplemental lighting of vegetable crops
– Daily light integral (DLI)
– Off-season local production
– Energy savings
– Designing arrays, fixtures, luminaires
– Minimize blockage of sunlight
– Apply supplemental LED light efficiently and effectively
Image courtesy of Erik Runkle and Daedre Craig, Michigan State University
Images courtesy of Christopher Currey, Michael Ortiz, Wesley Randall,
and Roberto Lopez , Purdue University
Pelargonium ‘Bullseye Scarlet’
HPS
100% R 85% R
15% B
70% R
30% B
Images courtesy of Ricardo Hernandez and Chieri Kubota, University of Arizona
Solar PPF = 345 mmol m-2 s-1
LED PPF = 55 mmol m-2 s-1
Hernández & Kubota
Technology developed by ORBITEC
Image from the work of C. Gomez and C. Mitchell, Purdue University
Intracanopy LED Lighting Towers
Technology developed by ORBITEC
Image from the work of C. Gomez and C. Mitchell, Purdue University
Point-of-View Summary
• LEDs will contribute to basic plant photobiology
– Narrow spectrum light
– Less cumbersome than classic photobiology equipment
• LEDs will be useful for whole-plant research
– Scalable, selectable waveband, high-output, long duration
• Translation to commercial application
– Systematic proof-of-concept testing required
– Multi-disciplinary teams required
• LEDS may not be best choice for all plant applications
Orbital Technologies Corporation
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Acknowledgements
Dr. A.J. Both, RU
Mike Bourget, ORBITEC
Daedre Craig, MSU
Chris Currey, PU
Celina Gomez, PU
Ricardo Hernandez, UA
Dr. Chieri Kubota, UA
Dr. Roberto Lopez, PU
Dr. Gioia Massa, PU
Dr. Bob Morrow, ORBITEC
Michael Ortiz, PU
Lucie Poulet, PU
Wesley Randall, PU
Dr. Erik Runkle, MSU
UA =
MSU =
PU =
RU =
SCRILED Project