1. Light measurement protocol for screens Gert-Jan Swinkels Wageningen UR Greenhouse Horticulture

2. Background No standard protocol available for measuring transmission horticultural screens Different screen manufacturers and research institutes use different methods o Light box o Integrating sphere o Integrated value (lux) o Wavelength dependant (spectrometer) o Normal / angular Comparison of transmission values within the horticultural industry is difficult

3. Approach Measurement protocol for covering materials (TNO-WUR) as starting point Test measurements to determine critical dimensions Investigate difference between single beam and double beam measurement

4. Equipment Integrating sphere  Collects and transmitted (scattered) light  High reflective coating, suitable for wavelength range (BaSO 4 for VIS, spectrolon (UV-IS-NIR)  Intensity decreases rapidly with increasing sphere diameter

5. Equipment Detector  Spectrometer (monochromator / array)  Protected by from first order light rays

6. Methods Single beam measurement  Transmission is the relative light intensity with and without sample  Because of the higher internal sphere reflectance with sample the measured transmission is overestimated (single beam substitution error) WUR, 2005-2011

7. Methods Double beam measurement  Comparing light intensity of two light paths: open port (air) and with sample  More stable and accurate than single beam but more complex WUR, 2005-2011

8. Critical dimensions Basic rule: The entire beam which enters the sphere through the open port should be able to enter the sphere after passing the sample Beam spot size  smaller or larger than the sample port size  Using a smaller beam, beam small enough to prevent light loss due to scattering  Light loss due to reflection inside the sample or scattering  Illuminated area large enough to cover patterns or structures. Rule of thumb: at least 10 repeating structures

9. Critical dimensions Angular measurements  Sample must be large enough to prevent illumination of the sides  Beam divergance influcences angular accuracy  1° angular error  3% measurement error at higher angles

10. Orientation  For structures or patterns which repete not equally in all orientations the transmission should be measured for differerent orientations of the sample  The overall transmission can be calculated as the plain average of all orientations

11. Single beam substitution error  Relation between port fraction and the single beam substitution error  On base of test measurements with different port sizes

12. Single beam substitution error Port diameter in relation to sphere diameter

13. Direct transmission  Single beam  Double beam  Weighted average in PAR range according to NEN2675

14. Hemisferical transmission  On base of a angular transmission  Standard 0°, 10°, 20°,.., 80°  Dependent on the sample, on base of different orientations  Spline interpolation

15. Meetapparatuur Wageningen UR PerkinElmer LAMBDA 950 UV/VIS/NIR Spectrophotometer met 270 mm Integrating Sphere Accessory (UL270)  Loodrechte transmissie en reflectie (300 - 2500 nm)  Meting loodrechte transmissie van diffuse materialen mogelijk www.omtsolutions.com

16. Meetapparatuur Wageningen UR Transvision  1 meter bol met 8 - 38 cm monsterpoort  Bereik 350 – 1100 nm, binnenkort tot 2300 nm  Meting dikke meerlaagse materialen mogelijk  Meting van: ● Hoekafhankelijke transmissie (0 – 80°) ● Hemisferische transmissie ● Reflectie voor loodrecht en diffuus licht ● Haze

17. Questions ?