Comparing BSDF data from a real and a virtual goniophotometer

Transcription

1 Comparing BSDF data from a real and a virtual goniophotometer Andreas Noback +, Lars O. Grobe*, Stephen Wittkopf * + Technische Universität Darmstadt * Competence Centre Envelopes and Solar Energy (CC-EASE), Lucerne University of Applied Science and Arts 15 th International Radiance Workshop , Padua, Italy

2 Outline Why would you compare BSDF data from a real and a virtual goniophotometer? How to simulate a goniophotometer with Radiance photon mapping? How to compare high resolution BSDF data? What are the results? Outlook 2

3 Why would you compare BSDF data from a real and a virtual goniophotometer? Approve your models, quantify errors Understand the (unexpected) results of your measurements Find and quantify differences between design and production samples of optical components 3

4 Scanning goniophotometer PAB Advanced Technologies PG-2 Image: PAB Advanced Technologies Ltd. 4

5 Implement a virtual goniophotometer with Radiance pmap: Illumination system void light lampmat lampmat source lampobj void plastic bafflemat 5 bafflemat ring baffleobj void antimatter photonmat 1 void photonmat ring photonobj

6 Implement a virtual goniophotometer: Illumination system Works well for a collimated beam Edge bias and half shadow is similar to falloff of the illumination system Works less good for smaller 4 beams θ i = φ i = Measurement Simulation 6 5 Irradiance on sample [W/m 2 ] 6 5 Irradiance on detector [W/m 2 ] 3 2 DSF [sr -1 ] distance from axis [m] receiver elevation angle θ [degree] θ s [ ]

7 Hochschule Luzern Implement a virtual goniophotometer with Radiance map: Sensor positions [header] #datapoints_in_file #format: theta [ ] 5597 phi DSF 1.29e e e e e e e e e-3 Images a-c: PAB Advanced Technologies Ltd. 7

8 Hochschule Luzern Implement a virtual goniophotometer with Radiance pmap: Sensor sphere void antimatter photonmat 1 void receivermat bubble receiverobj 41 1m 8

9 Implement a virtual goniophotometer with Radiance pmap: Sample xform -ry $thetain -rz $phiin 9

10 Implement a virtual goniophotometer with Radiance pmap: Sample y z x 1

11 Implement a virtual goniophotometer with Radiance pmap: mkpmap and rtrace Bandwidth 1K photons: Irradiance on detector [W/m 2 ] receiver elevation angle θ [degree] Bandwidth 1K photons: Irradiance on detector [W/m 2 ] receiver elevation angle θ [degree] Bandwidth 1K photons: Irradiance on detector [W/m 2 ] receiver elevation angle θ [degree] Bandwidth 1M photons: Irradiance on detector [W/m 2 ] receiver elevation angle θ [degree] mkpmap -apo photonmat -aps receivermat -apg sample.gpm 8 sample.oct rtrace $rtrace_opts -ap 2 -ab -1 sample.oct 11

12 Implement a virtual goniophotometer with Radiance pmap: mkpmap and rtrace cat input_vectors.dat \ rcalc -e '$1=$1; $2=$2; $3=$3; $4=-.1*$1; $5=-.1*$2; $6=-.1*$3' \ rtrace $rtrace_opts $pmapstring sample.oct > $out.dat input_vector.dat = output pg2 [header] #datapoints_in_file 5597 #format: theta phi DSF e e e e e e e-3 [ ] 12

13 Hochschule Luzern Implement a virtual goniophotometer with Radiance pmap: Results ɸs= θs= 9 τs2 τs1 DSF = -1 ɸs= 18 θs= 27 DSF Measurement θi = DSF Simulation θi = 35

14 Implement a virtual goniophotometer with Radiance pmap: Results θ i =35 φ i = θ i =45 φ i = θ i =3 φ i = 5 4 τ S τ ω 5 4 τ S V1 (sample) V2 (design geometry) V V1 (sample) V3 3 2 DSF [sr -1 ] 3 2 DSF [sr -1 ] 8 6 DSF [sr -1 ] θ s [ ] θ s [ ] θ s [ ] 14

15 How to compare high resolution BSDF data: Global and local accordance Global accordance f A,B = 1 1 v u t n  j=1 n  j=1 1 2 DSF A,j DSF B,j 2 C DSF A,j + DSF B,j A The metric has been designed to compare measurements of lumina Local accordance f j,a,b = 1 1 DSF A,j DSF B,j DSF A,j + DSF B,j! To relate global accordance to scattering behaviour that is significant for the 15

16 dw,v3,v1 14% 28% Hochschule Luzern ocal Level of Accordance f global accordance f A,B for the models is between 65% 84% except for model V2 at nerally higher for V3 as for V2 (Table 4). How to compare high resolution BSDF data: Global and accordance obal accordance of models V2 local and V3 with the measurements (V1) expressed in f A,B. ccordance of the reference beams ( f RB ) of the physical and virtual (VGP) illumination ven for comparison. qi f V2,V1 f V3,V1 f RB 92% 75% 84% 2% 74% 68% 7% 65% 71% 66% 74% Global accordance ccordance f j,a,b is low for the lowest DSF. This extends to the diffuse background cordance is achieved for lower DSF. Along the ridge the accordance is low in gaps n the simulation and at the edges of these peaks (Figure 1c). onally resolved comparison (Figure 1) shows that the scattering behaviour of the resembles the production sample (V1) in many details while some differences have to om redirected light (ts ) is continuous in the measurements. In both simulations this sts of separated peaks. This is a visible effect from the tessellation of the geometric light is reflected in a few discrete directions depending on the number of surfaces Tessellation is challenging for complex optical components of a small scale that leads Local accordance θ = 35 gnifications. This challenge is characteristic for DRCsi that are meant to be mounted glazing. ridge 16 (q = 9 13 ) in the measurements is lower than the DSF in both he end of the s fn= %-1%

17 Compare high resolution BSDF data: More Results buildings Article Accordance of Light Scattering from Design and De-Facto Variants of a Daylight Redirecting Component Andreas Noback 1,2, Lars O. Grobe 1, * and Stephen Wittkopf 1 1 Competence Center Envelopes and Solar Energy, Lucerne University of Applied Sciences and Arts, 648 Horw, Switzerland; mail@noback.info (A.N.); stephen.wittkopf@hslu.ch (S.W.) 2 Faculty of Architecture, Technische Universität Darmstadt, Darmstadt, Germany * Correspondence: larsoliver.grobe@hslu.ch; Tel.: Academic Editor: Yuehong Su Received: 3 June 216; Accepted: 12 August 216; Published: 18 August 216 Abstract: For the systematic development of a small-scale daylight-redirecting louver system the impact of manufacturing on light scattering characteristics has to be quantified, localized and understood. In this research, the accordance of the measured scattering distributions of a de-facto production sample V1 with the computed predictions based on its design geometry V2 are quantified for selected incident light directions. A metric describing the global accordance of distributions is adapted to quantify their overall difference. A novel metric of local accordance allows further analysis. A particular low global accordance between V1 and V2 is found for an incident elevation q i = 35. To test the hypothesis that this result can be explained by observed geometric deviations, a simulation model V3 replicating these is compared to the design. The hypothesis is supported by the resulting high degree of accordance. The low local accordance for individual outgoing light directions indicates geometric non-uniformity of the sample V1. This method has been found useful for product development and quality assurance. Beyond their application in the proposed method, global and local accordance have potential applications in all fields of light scattering measurements. Keywords: daylight redirection; BSDF; light scattering; simulation; goniophotometry; manufacturing deviation; quality assurance 17

18 Outlook How important are deviations from production for daylight autonomy or glare? Are there alternate metrics? How to compare data with deviating resolution? What is the relation of angular resolution and components size? Further Applications? How to get reliable BSDF for DRCs: repeat measurements, change sample size, measure multiple samples? Model the condenser system and optical bench of PG-2: would allow smaller beams and focus points. Suggestions? 18

19 Thank you for your attention! This research was supported by the Swiss National Science Foundation as part of the project Simulation-based assessment of daylight redirecting components for energy savings in office buildings (#14753). 19