A HighA HighA HighA High----Intensity, VariableIntensity, VariableIntensity, VariableIntensity, Variable----Spectra LED Spectra LED Spectra LED Spectra LED

Array for Plant Production in Challenging Array for Plant Production in Challenging Array for Plant Production in Challenging Array for Plant Production in Challenging

EnvironmentsEnvironmentsEnvironmentsEnvironments

David Hawley1, Michael Stasiak1, Jamie Lawson1, Alan Scott2, Per Aage Lysaa3, Mike A. Dixon1.

1Controlled Environment Systems Research Facility, University of Guelph, Guelph, Ontario, Canada; 2COM DEV Ltd., Kanata Ontario,

Canada; 3Intravision Group AS, Snaroya Norway.

6th International AgroSpace Workshop

Sperlonga, May 2014

ObjectivesObjectivesObjectivesObjectives

The aim of this study was to develop an array capable of emitting

variable spectra using multi-coloured, narrow-bandwidth LEDs.

The array would then be used to design high-resolution light

“recipes” for eliciting targeted responses.

LED selectionLED selectionLED selectionLED selection

655 nm

627 nm

591 nm

530 nm

505 nm

470 nm

440 nm

AssemblyAssemblyAssemblyAssembly

AssemblyAssemblyAssemblyAssembly

AssemblyAssemblyAssemblyAssembly

Assembly

Wiring and PowerWiring and PowerWiring and PowerWiring and Power

Wiring and PowerWiring and PowerWiring and PowerWiring and Power

• Constant current of 700 mA

• Required forward voltages ranged from 1.8 – 2.55 V,

depending on colour

• Colours outside the visible spectrum required much greater

voltage

• Four channels per ballast

• One ballast per colour

• 12 clusters of one colour in an array

One channel:

(2.55V x (3 clusters of 7 LEDS)) ���� 53.55 V at 700 mA == 37.49 W

Four channels:

37.49 W x 4 channels == 149.96 W.

Intensity CharacterizationIntensity CharacterizationIntensity CharacterizationIntensity Characterization

Intensity CharacterizationIntensity CharacterizationIntensity CharacterizationIntensity Characterization

1

2

3

4

5

A B C D E

1300-14001200-13001100-12001000-1100900-1000800-900

ExperimentsExperimentsExperimentsExperiments

1. Germination

2. Photosynthesis during vegetative growth

3. Adaptation

Experiments Experiments Experiments Experiments ---- GerminationGerminationGerminationGermination

• 8 species � wheat, barley, radish, lettuce, tomato,

soybean, kale, pepper

• 16 h photoperiod

• 7 monochromatic light qualities, HPS, darkness

• 22 °C ± 0.5 °C

• PAR = 280 µmol/m2/s

Experiments Experiments Experiments Experiments –––– GerminationGerminationGerminationGermination

Experiments - Germination

Experiments - Germination

Summarized Results Summarized Results Summarized Results Summarized Results ---- GerminationGerminationGerminationGermination

• Sensitivity to light quality varies between species

• Longer wavelengths favourable to some species while

completely inhibitory to others

• Shorter wavelengths were generally inhibitory to

germination

• Possible competition between photoreceptors in regards

to germination regulation

Experiments Experiments Experiments Experiments ---- PhotosynthesisPhotosynthesisPhotosynthesisPhotosynthesis

• Lettuce, tomato, pepper

• 39 light qualities

• Net CO2 assimilation rates

measured

• Photosynthesis compared on

a leaf area basis

"WHITE"

RB BL CY GN

OFF OFF OFF

RB BL CY DR

OFF OFF OFF

RB CY RD DR

OFF OFF OFF

RB A RD DR

OFF OFF OFF

GN A RD DR

OFF OFF OFF

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- LettuceLettuceLettuceLettuce

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- LettuceLettuceLettuceLettuce

Lettuce: Code 8-L

DR

-GN

-CY

-GN

RB

A R

D D

RA

RD

DR

RD

DR

0

50

100

150

Light Quality

Rela

tive c

arb

on a

ssim

ilati

on (

whit

e=100%

)

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- TomatoTomatoTomatoTomato

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- TomatoTomatoTomatoTomatoTomato: Code 8-T

A

-CY

-BL -C

YR

B A

RD

DR

A R

D D

R

RD

DR

0

50

100

150

Light Quality

Rela

tive c

arb

on

assim

ilati

on

(w

hit

e=

100%

)

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- PepperPepperPepperPepper

Photosynthesis Photosynthesis Photosynthesis Photosynthesis ---- PepperPepperPepperPepperPepper: Code 8-P

-DR

-BL -C

YR

B A

RD

DR

GN

A R

D

RB

DR

0

50

100

150

Light Quality

Rela

tive c

arb

on

assim

ilati

on

(w

hit

e=

100%

)

Summarized Results Summarized Results Summarized Results Summarized Results ---- PhotosynthesisPhotosynthesisPhotosynthesisPhotosynthesis

• Longer wavelengths are favourable for lettuce

• Light qualities devoid of longer wavelengths are inhibitory

to tomato

• While some light qualities were more favourable than

others, for pepper there was not a trend favouring any

specific spectra

Adaptation Adaptation Adaptation Adaptation –––– ShortShortShortShort----termtermtermterm

• Alternate between most

favourable and inhibitory light

qualities every 4 hours

Adaptation Adaptation Adaptation Adaptation –––– ShortShortShortShort----termtermtermterm

short term adaptation

GN

/CY

(0-4

h)

DR

(5-8

h)G

N/C

Y (9

-12h

)

DR

(13-

16h)

0.00

0.01

0.02

0.03

0.04

Light Quality

Ph

oto

syn

thesis

(µm

ol/m

2/s

)

Adaptation Adaptation Adaptation Adaptation –––– MidMidMidMid----termtermtermterm

• Measured photosynthesis on day 1 (initial) under

monochromatic light qualities

• Adapted plants for 3 days to a different light quality

• Measured photosynthesis on day 5 (final) under initial light

qualities

• Compared initial and final photosynthetic rates

Adaptation Adaptation Adaptation Adaptation –––– MidMidMidMid----termtermtermterm

Day 1 Day 5Day 2 Day 3 Day 4

measure measureadapt adapt adapt

Day 1 Day 5Day 2 Day 3 Day 4

measure measureadapt adapt adapt

Day 1 Day 5Day 2 Day 3 Day 4

measure measureadapt adapt adapt

Adaptation Adaptation Adaptation Adaptation –––– MidMidMidMid----term term term term –––– white white white white

adaptation - white

pre-a

mber

post-a

mber

pre-g

reen

post-g

reen

pre-d

eep r

edpost

-dee

p red

pre-c

yan

post-c

yan

pre-r

oyal b

lue

post-r

oyal b

lue

pre-r

edpost

-red

pre-b

lue

post-b

lue

pre-R

B G

N D

R

post-R

B G

N D

Rpre

-white

post-w

hite

-0.01

0.00

0.01

0.02

0.03

Light qualities, pre and post adaptation

Ph

oto

syn

thesis

(µ

mo

l/m

2/s

)

adaptation - amber

pre-a

mber

post-a

mber

pre-g

reen

post-g

reen

pre-d

eep r

edpost

-dee

p red

pre-c

yan

post-c

yan

pre-r

oyal b

lue

post-r

oyal b

lue

pre-r

edpost

-red

pre-b

lue

post-b

lue

pre-R

B G

N D

R

post-R

B G

N D

Rpre

-white

post-w

hite

0.00

0.01

0.02

0.03

Light qualities, pre and post adaptation

Ph

oto

syn

thesis

(µ

mo

l/m

2/s

)

Adaptation Adaptation Adaptation Adaptation –––– MidMidMidMid----term term term term –––– amberamberamberamber

Adaptation Adaptation Adaptation Adaptation –––– MidMidMidMid----term term term term –––– royal blueroyal blueroyal blueroyal blue

adaptation - royal blue

pre-a

mber

post-a

mber

pre-g

reen

post-g

reen

pre-d

eep r

edpost

-dee

p red

pre-c

yan

post-c

yan

pre-r

oyal b

lue

post-r

oyal b

lue

pre-r

edpost

-red

pre-b

lue

post-b

lue

pre-R

B G

N D

R

post-R

B G

N D

Rpre

-white

post-w

hite

-0.005

0.000

0.005

0.010

0.015

0.020

Light qualities, pre and post adaptation

Ph

oto

syn

thesis

(µ

mo

l/m

2/s

)

Summarized Results Summarized Results Summarized Results Summarized Results ---- AdaptationAdaptationAdaptationAdaptation

• Plants adapt to different qualities in different ways

• A recovery period may be required before photosynthetic

capacity is restored

• Examining more gradual light transitions in the future is

necessary to potentially reduce plant stress

General ConclusionsGeneral ConclusionsGeneral ConclusionsGeneral Conclusions1. Although darkness was most effective for stimulating

germination there are suggestions of unique light responses from some species.

2. In general, photosynthetic rates during the vegetative growth stages were highest when exposed to longer wavelengths, however some shorter wavelengths were equally effective in some cases.

3. Adaptation to light quality conditions may confound the interpretation of photosynthetic responses, especially if the changes to the light regime are made quickly.

4. We have an excellent experimental tool for investigating plant responses to light quality.

Future DirectionsFuture DirectionsFuture DirectionsFuture Directions

• Experiment with more light qualities, including UV

• Photosynthesis during reproductive development

• Determine photosynthetic recovery period for changing

light qualities

• Quantify synthesis of secondary compounds under varying

light qualities

AcknowledgementsAcknowledgementsAcknowledgementsAcknowledgements

• CESRF group

• Natural Sciences and Engineering Council (NSERC)

• Canadian Space Agency

• COM DEV Ltd.

• Ontario Centres of Excellence