Pieter de Visser& Gerhard Buck-Sorlin

Wageningen UR Greenhouse Horticulture* P.O. Box 430, 6700 AK Wageningen, The Netherlands

Simulation of light absorption and photosynthesis in a

greenhouse crop: effect of light node types & shaders

Evolution of lighting systems

Observed light distribution

bed1

pad1

bed2

pad2

bed3

pad3

bed4

pad4

bed5

pad5

bed6

pad6

bed7

14m

13m

12m

11m

10m

9m

8m

7m

6m

5m

4m

3m

2m

1m

C3 - afd 6.06 - 11nov09 - LEDs boven (20%af)

190-200

180-190

170-180

160-170

150-160

140-150

130-140

120-130

110-120

100-110

bed1

pad1

bed2

pad2

bed3

pad3

bed4

pad4

bed5

pad5

bed6

pad6

bed7

14m

13m

12m

11m

10m

9m

8m

7m

6m

5m

4m

3m

2m

1m

A3 - afd 6.06 & 7 - 28oct09 - SONT-50%

110-120

100-110

90-100

80-90

70-80

60-70

50-60

40-50

30-40

20-30

10-20

0-10

Why studying this?

• improve light interception, being driver of production

• even only 1% yield increase is appreciated: fine-tuning

• check stakeholders’ ideas about light climate with model

• efficient lighting strategies reduce energy use

Modelling platform: GroIMP

Main model parts:

Inversed path tracer model from GroIMP

3D mockup in XL of existing crop

Photosynthesis (Kim & Lieth, 2004)

Iight distribution

Iight absorption/reflection/transmission

?

Design of the virtual greenhouse

Measuring light with virtual sensors

• Sensor types• perceiving

• sphere with radius r • hemispheric view

(upper or upper/lower hemisphere)

• absorbing • planar• area amount of absorbed light∼• any planar object (e.g. leaf) can measure its light absorption directly

LENi

LENi+1

RU (divergence)

RL

LEN

DIAMRH (tilting)

L1

L2

L3

L4

L5

L6

L7

L1

L2

L3

L4

L5

L6

L7

T

RL (“hanging down”of leaflets)

SONT + LED at Improvement Centre, Bleiswijk, NL

Shader parameterization: a virtual set-up

Light types

Point light Directional light

Spotlight

SONT HPS-lamps

Measured light distribution

(two vertical planes,

perpendicular):

max. opening angle 140°

• New class SONT: extension of PointLight class of GroIMP

• Directional distribution of emitted light incorporated into the rendering process by overwriting method getDensityAt() (computes for a given direction probability density of choosing this direction.):

1) Transformation of direction vector ω = (x,y,z), |ω| = 1 into a polar form, where polar angles are:

Model of a SON-T lamp

φ = atan2

where atan2 = variant of arcus tangens function

ϕ = atan2(y,x)

θ = acos(z)

azimuth [-π < ϕ < π]

elevation [-π < θ < π]

2) Angles ϕ and θ used as indices for the lookup table λ of luminosity values. λ is discretized as an array of 36 by 180 values, for ϕ, respectively θ.

Mapping the values of ϕ and θ to λ and obtaining lower and higher indices for the two angles:

float a = (phi+PI) * 18 / PI;

float b = (theta+PI) * 90 / PI;

int phi0 = (int) a % 36;

int phi1 = (phi0+1) % 36;

int theta0 = (int) b;

int theta1 = min(179, theta0+1);

3) Bilinear interpolation to weight four drawn array values smoothing of spatial light distribution:float wa = 1 - (a-floor(a));

float wb = 1 - (b-floor(b));

Obtaining the array values from the lookup table:float d00 = li[phi0][theta0];

float d01 = li[phi0][theta1];

float d10 = li[phi1][theta0];

float d11 = li[phi1][theta1];

float w00 = wa*wb;

float w01 = wa*(1-wb);

float w10 = (1-wa)*wb;

float w11 = (1-wa)*(1-wb);

Multiplication of weighting factors with read luminosity values to obtain probability density of the ray for the given direction: float density = w00*d00 + w01*d01 + w10*d10 + w11*d11;

• Visualisation of light distribution of a SON-T assimilation lamp.

• Next step: implementation of such a lamp as a new light source in the modelling environment

Implementation of a Hortilux GreenPower SON-T lamp

First version (improper

interpolation between array

values)

Update: bilinear interpolation between array values; 3 different lamp angles to a reflecting sheet

Grid of 21 SON-T broad beam reflector lamps

reflection screen at

increasing distance

below the lamps

0.5 m

Quantifying light distribution in row crop: light type

Effect light type on distribution

light: SPOT DIRECT SPOT DIRECT

wall height (m) 4.5 4.5 3.5 3.5

South wall: fraction

40%unshaded

34% 16% 4%

North wall: 41% 38% 13% 15%

West wall: 41% 46% 13% 20%

East wall: 36% 38% 13% 29%

Plant shading is more stable at use of spot lights:

How many buffer rows?

200

220

240

260

280

300

320

340

360

380

0 0 1 2

nr. of border rows

Lig

ht

abso

rpti

on

by

inn

er p

lan

ts incl.front&back

no front&back

Validation of light module of tomato model

0%

20%

40%

60%

80%

100%

0 1 2 3 4 5

Height above ground (m)

Lig

ht in

tens

ity

.

model

observed

Check poster on comparison of two light models of tomato

Lighting strategies:

1. change SON-T position (horizontal & vertical) & angle

2. LED position above or between crop rows

3. path width between rows (at same plant density)

4. SON-T distribution wide vs. deep reflector

5. reflection via screen increases light use efficiency?

6. Effect lamp colour

Lamp light direction

Angle from vertical

Light absorbed(umol s-1)

Light level floor(umol s-1 m-2)

22° 1372 55

67 1890 30

90 1807 15

Lamp type, height; crop structure

Scenario: Absorbed light% of input

Light level on floor(umol m-2 s-1)

Default 92.7 9.00

Wide reflector 93.3 8.16

Lamp height -1m

95.2 7.95

Path width +0.4m

89.7 13.07

Idem, plants+24%

91.3 10.96

Testing opening angle

Effect opening angle (≃ type reflector):Available light in scene and crop absorption at 27

Phyto:

(umol in total)Opening angle: SONT

(Phyto) very small small wide wide deep

Light in (3) 1789 1790 1813 0.073 0.38

Light in (27) 1806 1811 1822 0.073 0.38

CropAbs 1213 1210 1213 0.049 0.25

% of IN 68% 68% 67% 68% 65%

LED scenarios:

Relation to LED position in the crop:

in path, in row, height

Wireframe in

sideview

Virtual crop

White: rows of virtual sensors

Vertical light distribution depending on LED position

N.B.: data averaged from 2 rows incl. path

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Height from ground (m)

Lig

ht

leve

l (u

mo

l m-2

s-1

)

LED on top

LED in row (3.5m)

LED in path (3.5m)

LED in row (2.5m)

Light absorption in crop: LED positioning in rowHeight 2.5m 3.5m top (4.6m)

Leaf 86.1% 93.2 89.8

Young fr 3.3 0.1 0.6

Ripe fr 0.2 0.0 0.1

Stems 4.7 0.9 1.0

Total: 94.2 94.2 91.6

RoofFloor

0.50.0

5.40.0

7.80.0 no aging:

RUE (rel.) 62.2 40.3 100 132

Light absorption in crop: LED positioning in pathHeight 2.5m 3.5m top (4.6m)

(row)

Leaf 86.0% 91.0 89.8

Young fr 6.0 0.8 0.6

Ripe fr 0.2 0.0 0.1

Stems 6.5 1.6 1.0

Total: 98.7 93.4 91.6

RoofFloor

0.50.0

5.80.0

7.80.0

RUE (rel.) 70.5 70.6 100

Conclusions:

1. Type of reflector hardly affects light utilization

2. Row structure (path width) has some impact on light use

3. LED positioning strongly affects light use

4. GroIMP platform suitable for this approach

Next steps and outlook:

1. Further optimize lighting strategy incl. screens

2. Include wavebands in light source and photosynthesis

3. Determine energy requirements for scenarios

4. Light on rose

5. Not a static, but a growing, adapting crop

6. Improve path tracer (Göttingen)

7. ..

Thank you for your attention!

Funded by:

Horticultural Production Board & Ministry of Agriculture