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Artificial Lighting Options For greenhouse‐and Indoor‐Based Hydroponic Lettuce Production
Krishna Nemali Ph.D.Assistant Professor and Extension Specialist
Department of Horticulture and Landscape ArchitecturePurdue University, West Lafayette
Tel: 765‐494‐8179Email: [email protected]
Lettuce requires a daily total of 15 to 20 mol/m2 of light
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How much sunlight do we get inside greenhouse?
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350
DLI (moles/m
2/day)
Chronological day
WinterWinter
Electrical energy consumption: KWh
Kilo Watt hour (KWh): A measure of electrical energy consumption; equivalent to 1000 W of electrical power consumed in an hour.
Electrical companies charge based on number of KWh ($11 to 13 cents/KWh)
Example: HPS lamps: 1000 W or 1 KWh
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Price per KWh is continuously increasing in the US
$235SE 400W $450DE 1000W 320 W $750
Supplemental lighting options for greenhouse
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T 8 Fluorescent ($ 100) Fluence RazrX ($320)
Phillips Green Power ($360) Total Grow ($ 340)
LED options for vertical farming
How to determine which lighting option is best for you?
Electrical Energy Efficiency (EEE)
Fixtures with highest EEE are the best
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EEE has two components•Photon Efficiency (PE)•Light Use Efficiency (LUE)
EEE = PE × LUE
Photon Efficiency (PE)
• It is light output per unit energy input
• Photon efficiency = /
/= 2.38 μ /J
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Electrical Cost vs. Photon Efficiency
Bench
Photon Efficiency
Highest
Lowest
8‐10’
1’
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Light Use Efficiency (LUE)
Weight of lettuce produced per mol of light received by plants (lb/mol)
What is a mole of light?‐ total light received in a unit area during crop growth
What is the difference between a mole of light received by these fixtures?
Red: Blue LED
Mole of light measures intensity but does not indicate what type or quality of light is included in the mole
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0
0.2
0.4
0.6
0.8
1
1.2
1.4400
411
422
433
444
455
466
477
488
499
510
521
532
543
554
565
576
587
598
609
620
631
642
653
664
675
686
697
Incident light
‐0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
400
411
422
433
444
455
466
477
488
499
510
521
532
543
554
565
576
587
598
609
620
631
642
653
664
675
686
697
Reflected Light
Why does light quality matter?
Green waveband is reflected more
Reflected light is wastedBlue Green Red
https://bam.files.bbci.co.uk/bam/live/content/zg4tvcw/large
Why does light quality matter?
Blue and green light is absorbed by non‐chlorophyll pigments
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Why does light quality matter?
Photosynthesis is lower under green light
20% Blue 60% Blue
Intensity received is similar but leaf area is smaller under more blue
Why does light quality matter?
358 cm2 286 cm2
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Fixture 1 Fixture 2vs.
Light Use Efficiency (LUE)
Weight of lettuce produced per mol of light received by plants (lb/mol)
Light quality in a mole of light received will affect crop growth and LUE
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EEE = PE × LUE
Engineering Plant Biology
Electrical Energy Efficiency
