Opportunities and challenges of light- emitting diodes for ...leds.hrt.msu.edu/assets/Meeting/Intracanopy-lighting.pdfOpportunities and challenges of light-emitting diodes for greenhouse

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Opportunities and challenges of light-emitting diodes for greenhouse

supplemental lighting

Celina Gómez and Cary A. MitchellLED Symposium

Tucson, AZFeb. 20th, 2015

Can LEDs be used as alternative supplemental lighting (SL) sources?

• Light quality effects on plant growth

• Physiological responses and productivity

• Energy savings potential

• Tomato as a model crop

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Metrics for plant lighting

• Photosynthetically Active Radiation

(PAR, 400-700 nm)

• Photosynthetic Photon Flux

(PPF, μmol·m-2·s-1)

• Daily Light Integral

(DLI, mol·m-2·d-1)

RationaleAverage greenhouse (GH) DLI across the contiguous US

December June

2.5 - 55 - 7.57.5 - 1010 - 12.5

12.5 - 1515 - 17.517.5 - 20

20 - 22.522.5 - 2525 - 27.527.5 - 30

After Korczynski et al., 2002

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GH tomato production in the US

Supplemental light (SL)

Important PAR source in Northern latitudes

• Additional DLI to enhance canopy photosynthesis and crop growth

• Frequently perceived as too expensive

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Overhead (OH) high-pressure sodium (HPS) lamps(current standard)

Wavelength (nm)

400 450 500 550 600 650 700

No

rma

lize

d P

ho

ton

Flu

x

0.0

0.2

0.4

0.6

0.8

1.0

Sunlight

HPS

13%, 49%, and 38% broadband blue, green, and red light, respectively*

*Broadband definitions:Blue (400-500 nm)Green (500-600 nm)Red (600-700 nm)

Backyard Farms, Madison, ME

Light-Emitting Diodes (LEDs)alternative sources for plant lighting

• Photon-emitting surfaces are not hot

• Placement close to leaves = lower photon emission

• Reduced photon emissions draws lower power

• Potential for advances in light distribution

• Efficiency is improving rapidly

• Wavelength selectableCool surface

Adequate PPF

Close to plants

Lighting system built by ORBITEC

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SL for transplant propagation

• natural light (control)

• natural + 100-W HPS lamp

• natural + supplemental LEDs:

– 100% red (R)

– 95% R and 5% blue (B)

– 80% red R and 20% blue B

• SL DLI: 5.1 mol·m‒2·d‒1

Gómez, C. and C.A. Mitchell. 2015. HortScience 50:1-7.

Peak λ of red and blue LEDs were 627 nm and 450 nm, respectively

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Broadband percentage of sunlight's blue, green, red (BGR)

The BGR percentages of midday solar PPF were similar across seasons

Treatment

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Bro

adb

and w

avele

nght

(%)

0

20

40

60

80

100

Light quality effects

Average solar DLI per experiment

0 2 4 6 8 10 12 14

Hyp

oco

tyl d

iam

ete

r (m

m)

0

1

2

3

4

Control

HPS

100% R - 0% B

95% R - 5% B

80% R - 20% B

0 2 4 6 8 10 12 14

Sh

oo

t dry

we

igth

(g)

0.00

0.05

0.10

0.15

0.20

0.25

Blue light in SL has potential to increase overall seedling growth compared to blue-deficient LED SL treatments in overcast, variable-DLI climates.

100% red

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Mutual shading between foliar canopies

Leaves under direct light

Shaded leaves

Intracanopy lighting (ICL)(from the work of Jonathan Frantz and Cary Mitchell, Purdue University)

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Reconfigurable ICL- vs. OH-LED arrays(from the work of Gioia Massa and Cary Mitchell, Purdue University)

Intracanopy LED (ICL-LED) SLTechnology developed by ORBITEC

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Four consecutive 5-month experiments:

• Two winter-to-summer (Expt. 1 and 3)

• Two summer-to-winter (Expt. 2 and 4)

– Overhead high-pressure sodium (OH-HPS) lamps– Intracanopy LED (ICL-LED) towers (95% red and 5% blue)– Unsupplemented controls

Gómez, C. and C.A. Mitchell. 2014. Acta Hort. 1037:855-862.

Gómez et al., 2013. HortTechnology 23:93-98.

Experiment No.

1 2 3 4

Fru

it y

ield

(kg m

-2)

0

10

15

20

OH-HPS

ICL-LED

Control

In general, there were no differences between the two SL treatments for any of the growth or yield parameters evaluated.

aa

b

a

a

b

a a

b

aa

a

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Expt. 1

DAT

0 20 40 60 80 100 120 140 160

Energ

y c

onsum

ed (

kW

h/d

)

0

20

40

60

80

100

120

140

160

180

OH-HPS

ICL-LED

Expt. 2

DAT

0 20 40 60 80 100 120 140 160

Energ

y c

onsum

ed (

kW

h/d

)

0

20

40

60

80

100

120

140

160

180

OH-HPS

ICL-LED

Expt. 4

DAT

0 20 40 60 80 100 120 140 160

Energ

y c

onsum

ed (

kW

h/d

)0

20

40

60

80

100

120

140

160

180

OH-HPS

ICL-LED

Expt. 3

DAT

0 20 40 60 80 100 120 140 160

Energ

y c

onsum

ed (

kW

h/d

)

0

20

40

60

80

100

120

140

160

180

OH-HPS

ICL-LED

Daily energy consumption

winter-to-summer

summer-to-winter

Constant DLI of 9 mol·m-2·d-1

Reduction in energy consumption due to ICL-LED

*DAT= days after transplanting

1. 600 W OH-HPS lamps2. Hybrid lighting (OH-HPS + interlighting) 3. Intracanopy-LED towers4. Unsupplemented control

LL1*

LL3

LL2

*LL = leaf layer

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Status of comparative studyWinter-to-summer ‘14

• SL increased fruit yield by at least 33% compared to control

• Energy consumed by hybrid SL was intermediate between that of OH-HPS and ICL-LED

• LEDs accounted for 38% of the total energy consumed by hybrid SL

• Leaf photosynthetic capacity was similar across LLs when grown under ICL-LED or hybrid SL

• Amax (maximum gross CO2 assimilation) was 48% (OH-HPS) or 60% (control) lower in LL3 compared to LL1

• No differences in yield among SL treatments

• Higher source activity does not always lead to yield increases

What are some of the challenges?

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Overhead lighted

Intracanopy lighted

‘Triton’ pepper

Plants look OK underred + blue LEDs

But under white light….

It is much easier to diagnoseplant health under broad-spectrum white light than under monochromatic light

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Hard to visually assess plant health

“Photobleaching”

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Intumescence

(Re)-discovering the solar spectrum

• Adding green to overhead red + blue light promotes growth

• Adding far-red– Promotes stem elongation– Promotes flowering in some photoperiodic classes– Prevents intumescence growth in some species

• Adding UV– Prevents intumescence growth– Promotes pigment and phytochemical accumulations

• Are white LEDs the answer?– Are blue LEDs + phosphor– Lack FR, UV– Electrically inefficient compared to monochromatic LEDs

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A. 80% R and 20% far-red (FR)B. 10% B and 90% RC. Unsupplemented controlsD. 25% B, 60% R, and 15% FRE. 30% B and 70% R

Finding the optimum SL spectrum(if there is one…)

Thank you!

Questions?

[email protected]

Celina GómezDepartment of Horticulture & Landscape Architecture

Purdue University625 Agriculture Mall Drive

West Lafayette, Indiana 47907-2010 USA(765) 496-2124