The spectral bidirectional scatter distribution function (BSDF) offers a complete description of the spectral and spatial optical characteristics of a material. Any gloss and color measurement can be related to a particular value of the BSDF, while accurate luminaire design with ray tracing software requires the BSDF of reflectors and filters. Many measuring instruments, each having particular advantages and limitations, have been reported in the literature, and an overview of these instruments is included. A measuring instrument that allows for an absolute determination of the spectral BSDF with a full three dimensional spatial coverage in both reflectance and transmittance mode, a broadband spectral coverage, a large dynamic range, a reasonable acquisition time, and a large sample illumination area is presented. The main instrument characteristics are discussed, and the measurement capabilities are illustrated.
"This plate is meant to be excited by pump-LEDs whose emission peak is about 450 nm, resulting in white light with a CCT of 3000 K. The BSDF for the phosphor plate was characterized with the setup described in , consisting of a goniometer with a fixed position light source and a mobile detector, with a position and inclination adjustable sample holder in between the light source and the detector. For every incident polar angle (θ i =5°, 45°, 56°) the scattered spectral flux was measured for the scattered polar angles 0°≤θ s ≤90° in the incident plane in increments of 5° for both the reflection (backwards) and transmission (forwards) hemispheres. "
[Show abstract][Hide abstract] ABSTRACT: Light extraction efficiency in SSL with conformal phosphor-converted LEDs can be enhanced with remote phosphor LED technology which allows the extraction of backscattered light and lowers the thermal operation point of the phosphor. In this study, a remote phosphor module was simulated using ray tracing software. The BRDF of the reflective material in the cavity was determined, a ray file was obtained for the blue pump LEDs, and the remote phosphor component was modeled with experimentally obtained bi-spectral BSDF data. Simulation and experimental results match in the near and far field behaviour.
18th Annual Symposium of the IEEE Photonics Society Benelux Chapter, Eindhoven, The Nederlands; 11/2013
"Some are dedicated only to measure the light backscattered by the media [1– 4]. Others are used to estimate the light reflected and/or transmitted  . A few of them are to measure polarized BRDF at fixed wavelength, and they often take into account an angular resolution of the BRDF ranging from 2° to 10°   . "
[Show abstract][Hide abstract] ABSTRACT: Multispectral and polarized light reflectance measurements are very useful to characterize materials such as paint coatings. This article presents an overview of an automated high-angular resolved, in-plane multispectral polarized reflectometer and its calibration process. A compre-hensive study based on multispectral BRDF and DOLP measurements is conducted on different colour and glossy aspects of paint coatings. An original inverse method from in-plane measurements is used to model the out-of-plane BRDF and to investigate the role of the surface and subsurface scattering phenomena in its components.
[Show abstract][Hide abstract] ABSTRACT: Light-emitting diode (LED) technology is developing very quickly and may be considered an alternative for traditional light sources. However, at this moment, manufacturers and end users of LEDs are facing a rather basic but major problem. The lack of standardization regarding optical and electrical characterization of LEDs appears to compromise a successful implementation. In particular, numbers quoted for the luminous flux, and consequently for the efficacy of LEDs, are very sensitive data because they are used to impress and push the LED market. In this paper, the most was made of the typical hemispherical radiation of high-power LEDs to increase the accuracy of the flux determination using a custom-made integrating sphere. Recently developed measurement techniques such as the use of an external spectral irradiance standard and an optimized spectral irradiance detection head are combined with a very particular port geometry and a minimized baffle area. This results in a uniform spatial response distribution function (SRDF), which guarantees an accurate radiant and luminous flux determination, irrespective of the spatial intensity distribution of the LED package or luminaire. The effect of the directional response of the detector head on the SRDF has been explored. Measurements on LED devices with and without external optics are presented, illustrating the possibilities of the measurement setup.
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