Light transmission and distribution in vegetable greenhousesCanadian Greenhouse Conference, 5 October 2016, Niagara Falls, Canada

Dr. Silke Hemming, Wageningen University & Research Centre

Light is (almost) never too much:

yield increase per% light increase

Crop % Yield increase

Lettuce 0.8Radish 1Cucumber 0.7−1Tomato 0.7−1Rose 0.8−1Chrysanthemum 0.6Pointsettia 0.5−0.7Ficus benjamina 0.6

Source: Marcelis et al., 2006

Diffuse light

Potential diffuse light in different climates

Amount of direct / already diffuse light varies in different climates

Cold winter climate e.g. The NetherlandsMild winter climate

e.g. Mediterranean (Semi-)arid climate

e.g. Middle-East

Increase potential of diffuse coverings

Hemming et al. (2008)

Diffuse light – crop effects

Li (2014)

Horizontal light distribution at crop level

123456

0

20

40

60

80

100

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500

Pad

Lich

tinte

nsite

it (%

)

Lengte rij ( cm )

Ref

123456

0

20

40

60

80

100

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500

Pad

Lich

tinte

nsite

it (%

)

Lengte rij ( cm )

Diff71

Reference

Diffuse71

Dueck et al. (2012)

Diffuse light – crop effects

Li (2014)

0

50

100

150

200

250

0 20 40 60 80 100

Cro

p he

ight

[cm

]

Light interception [%]

April 25th, 2006

ClearDiffuse

0

50

100

150

200

250

0 20 40 60 80 100

Cro

p he

ight

[cm

]

Light interception [%]

May 3rd, 2006

ClearDiffuse

0

50

100

150

200

250

0 20 40 60 80 100

Cro

p he

ight

[cm

]

Light interception [%]

May 23rd, 2006

ClearDiffuse

Vertical light distribution in crop - cucumber

Hemming et al. (2007)

Diffuse light – crop effects

Li (2014)

Photosynthesis net - high-wire cucumber

Dueck et al. (2009)

Photo-inhibition - tomato

Dueck et al. (2012)

Diffuse light – crop effects

Li (2014)

0

25

50

75

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30Weeks

Cum

ulat

ief p

rodu

ctie

(kg/

m2)

Hoog diffuusLaag diffuusControle

Crop yield - cucumber high-wire

Diffuse light: 9% higher cucumber production (crop planted in March)

+9.2%

+6.5%

Weeks

Prod

uctio

n(k

g m

-2)

High diffuse

Low diffuse

Control

Dueck et al. (2008)

Diffuse light sweet pepperca. 5% more yield

Diffuse light cucumber4-10% more yield

Hemming et al. (2006, 2008)

Diffuse light tomato8-10% more yield

Plas

tic f

ilms

Increased light scattering

Gla

sses

Diffuse light

Optical properties – light quantity

Light (PAR)

Transmission

Reflection

Absorption

increases

decreases

Covering material

1 – Absorption – Reflection = Transmission

Measurement light quantity

20

Wageningen UR TransvisionIntegrating Sphere for

hemispherical light transmission measurement

∫∫

∫∫= 2/

0

2

0

2/

0

2

0

)cos()sin(),(

)cos()sin(),(),(

pipi

pipi

HEM

ddI

ddITT

φθθθθφ

φθθθθφθφ

Transmission τ [%]

Angle of incidence 𝜭𝜭i [o]

Measure angular and hemispherical light transmissionNOT perpendicular light transmission

Transmission

Geometrical distribution

Optical properties – light geometricaldistribution

Light

Diffuse structure

Covering material Diffuse pigments

Light (PAR)

Materials and Methods - Equipment

22

Radiant IS-SA Imaging Sphere for Scatter and Appearance

Measurement at Wageningen UR Lightlab

Measure Haze or even better BTDF scattering

Diffuse coverings – plastics

Plastic films

Hemispherical light transmission τh vs. haze η

y = -0.16x + 85.6R² = 0.41

50

55

60

65

70

75

80

85

90

95

100

0 10 20 30 40 50 60 70 80 90 100

hem

isp

her

ical

tra

nsm

issi

on [

%]

haze [%]

Diffuse coverings - PE/EVA plastic films

Code Material Hazeη

Hemisphericaltransmission

τh

PK14A Clear film AD 23 81.3

PK14C Normal film 49 77.1

PK14D Normal film AD 60 74.7

PK14B Extra diffuse film 97 68.9

Amount of lightAmount of scattering

Light Diffusing Materials – high η, high τh

0 10 20 30 40 50 60 70 80 90 100

HDPE high diffusion,80µm BR

HDPE mediumdiffusion, 80µm BR

ETFE high diffusion,100 µm AS

ETFE mediumdiffusion, 80 µm AS

haze hemispherical transmission

Diffuse coverings – glasses

Glasses

Diffuus en anti-reflectie: transmissie

material hazehemispherical transmission

A 0 0 84.4A 0 AR 87.1A 0 ARAR 90.2A LH 20-30 83.6A LH AR 86.2A LH ARAR 89.2A HH 70-80 79.7A HH AR 82.2A HH ARAR 84.3

+2.5-3%per side

Results - glass

Material

Cod

e

Lig

ht

tran

smis

sion

per

pen

dic

ula

r

Lig

ht

tran

smis

sion

hem

isp

her

ical

Haz

e

F-sc

atte

r

τp τh η ΦTraditional greenhouse glass PLA09 90.4 82.7 4 0Clear glass* R0 97.4 90.2 4 0Matt/matt glass low diffusion* SG20 95.9 89.2 20 4Matt/matt glass medium diffusion* SG45 95.3 87.5 46 22Prismatic glass high diffusion* SG80 95.2 84.3 78 54Etched glass high diffusion* DA80 98.0 86.0 83 59Etched glass extra high diffusion* DA95 97.9 81.7 94 79Paraboloid glass extra high diffusion SG95 75.0 69.1 97 82Motheye microlens extra high diffusion NO12J 76.6 70.1 100 98Lambertian diffusor L100 44.6 40.4 100 100

* with anti-reflection coating

Results - glass

Material

Cod

e

Lig

ht

tran

smis

sion

per

pen

dic

ula

r

Lig

ht

tran

smis

sion

hem

isp

her

ical

Haz

e

F-sc

atte

r

τp τh η ΦTraditional greenhouse glass PLA09 90.4 82.7 4 0Clear glass* R0 97.4 90.2 4 0Matt/matt glass low diffusion* SG20 95.9 89.2 20 4Matt/matt glass medium diffusion* SG45 95.3 87.5 46 22Prismatic glass high diffusion* SG80 95.2 84.3 78 54Etched glass high diffusion* DA80 98.0 86.0 83 59Etched glass extra high diffusion* DA95 97.9 81.7 94 79Paraboloid glass extra high diffusion SG95 75.0 69.1 97 82Motheye microlens extra high diffusion NO12J 76.6 70.1 100 98Lambertian diffusor L100 44.6 40.4 100 100

* with anti-reflection coating

Results- BTDF glass

2D plot of calculated angular energy distribution E(𝜃𝜃𝑡𝑡) based on measured BTDF of different glasses

31

η=94%

η=97%

η=100%

η=100%

Φ=79%

Φ=82%

Φ=98%

Φ=100%

Conclusions diffuse materials

Measure hemispherical light transmission & haze & Fscatter

Covering materials with higher light scattering increase production (at same light transmission!)

Materials with different scattering distribution (Fscatter) are available, choose right material for crop

Covering materials with significantly reduced hemispherical transmission can cause production decreases (if light is limiting factor)

Other materialsScr

eens

Increased light scattering

Coa

tings

Thank you for your attention!

34