1 / 15

Light measurement protocol for screens

Light measurement protocol for screens. Gert-Jan Swinkels Wageningen UR Greenhouse Horticulture. Background. No standard protocol available for measuring transmission horticultural screens Different screen manufacturers and research institutes use different methods Light box

nedaa
Download Presentation

Light measurement protocol for screens

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 • Light box • Integrating sphere • Integrated value (lux) • Wavelength dependant (spectrometer) • 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 (BaSO4 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 rangeaccording 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. Questions ?

More Related