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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

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Evolution of lighting systems

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Observed light distribution

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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

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Modelling platform: GroIMP

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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 ?

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Design of the virtual greenhouse

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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

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LEN i LEN i+1 RU (divergence) RL LEN DIAM RH (tilting) L1 L2 L3 L4 L5 L6 L7 L1 L2 L3 L4 L5 L6 L7 T RL (hanging downof leaflets)

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SONT + LED at Improvement Centre, Bleiswijk, NL

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Shader parameterization: a virtual set-up

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Light types Point light Directional light Spotlight

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SONT HPS-lamps Measured light distribution (two vertical planes, perpendicular): max. opening angle 140°

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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]

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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);

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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);

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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;

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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

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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

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Grid of 21 SON-T broad beam reflector lamps reflection screen at increasing distance below the lamps 0.5 m

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Quantifying light distribution in row crop: light type

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Effect light type on distribution light:SPOTDIRECTSPOTDIRECT wall height (m)4.5 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:

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How many buffer rows?

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Validation of light module of tomato model Check poster on comparison of two light models of tomato

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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

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Lamp light direction Angle from vertical Light absorbed (umol s -1 ) Light level floor (umol s -1 m -2 ) 22°137255 67189030 90180715

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Lamp type, height; crop structure Scenario:Absorbed light % of input Light level on floor (umol m -2 s -1 ) Default92.79.00 Wide reflector93.38.16 Lamp height -1m95.27.95 Path width +0.4m89.713.07 Idem, plants+24%91.310.96

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Testing opening angle

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Effect opening angle ( type reflector): Available light in scene and crop absorption at 27 Phyto: (umol in total) Opening angle:SONT (Phyto)very smallsmallwide deep Light in (3)1789179018130.0730.38 Light in (27)1806181118220.0730.38 CropAbs1213121012130.0490.25 % of IN68% 67%68%65%

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LED scenarios: Relation to LED position in the crop: in path, in row, height Wireframe in sideview Virtual crop White: rows of virtual sensors

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Vertical light distribution depending on LED position N.B.: data averaged from 2 rows incl. path

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Light absorption in crop: LED positioning in row Height2.5m3.5mtop (4.6m) Leaf86.1%93.289.8 Young fr3.30.10.6 Ripe fr0.20.00.1 Stems4.70.91.0 Total:94.2 91.6 Roof Floor 0.5 0.0 5.4 0.0 7.8 0.0 no aging: RUE (rel.)62.240.3100 132

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Light absorption in crop: LED positioning in path Height2.5m3.5mtop (4.6m) (row) Leaf86.0%91.089.8 Young fr6.00.80.6 Ripe fr0.20.00.1 Stems6.51.61.0 Total:98.793.491.6 Roof Floor 0.5 0.0 5.8 0.0 7.8 0.0 RUE (rel.)70.570.6100

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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

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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...

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Thank you for your attention! Funded by: Horticultural Production Board & Ministry of Agriculture

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