New scanning gonio-photometer for extended BRTF measurements

Le résumé fourni par la source

Measured data of the angular distribution of light scattering by surfaces (bi-directional-reflection-transmittancefunction, BRTF) has use in many fields: among them are stray light in lens design, projection screens,1 advanced architectural glazings and validating of surface and material models. Existing measurement devices either use cameras to capture multiple outgoing directions (imaging gonio-photometers) or move the sensor around the sample (scanning gonio-photometers). Scanning gonio-photometers offer advantages from a physics point-of-view: e.g. angular resolution, angular coverage, no relaying optics, isotropic sensor response, dynamic range and spectral resolution. But they had been prone to slow measurement speed, up to rendering them de-facto impractical for batch processing or routine checks in some applications. A new design of a scanning, out-of-plane gonio-photometer is presented with optimised mechanical and electronic design, reduced scanning time, optimised sensors resulting in high dynamic range, low noise and extended measurement capabilities (e.g. VIS,IR,UV and polarisation). Since the unobstructed beam is used as reference, it does not need external reference standards for ab-initio BRTF values. Sample data and validation checks illustrate that this measurement design offers advantages and flexibility over previous concepts.

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