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The bidirectional scattering-surface reflectance distribution function (BSSRDF) describes the radiance originated by the volume scattering and the surface reflectance of any position on the surface of a sample, when it is directionally irradiated at any other position. The present state of the technology for appearance rendering requires a more detailed physical description of translucent objects by traceable measurements of the BSSRDF. This work presents two primary facilities developed for traceable BSSRDF measurements by different measuring approaches. Their results on the same translucent samples have been compared and the achieved BSSRDF scale has been transferred to a commercial measuring system. This study highlights the problems of the different measuring instrument designs and provides the scientific community with more knowledge on the measurement of the BSSRDF, which will be crucial for future works on material appearance.

In recent years, there has been a growing interest in the measurements of the bidirectional reflectance distribution function (BRDF) in industry and research and development. However, there is currently no dedicated key comparison to demonstrate the scale conformity. To date, scale conformity has been proved only for classical in-plane geometries, in comparisons between different national metrology institutes (NMIs) and designated institutes (DIs). This study aims at expanding that with nonclassical geometries, including, for the first time, to the best of our knowledge, two out-of-plane geometries. A total of four NMIs and two DIs participated in a scale comparison of the BRDF measurements of three achromatic samples at 550 nm in five measurement geometries. The realization of the scale of BRDF is a well-understood procedure, as explained in this paper, but the comparison of the measured values presents slight inconsistencies in some geometries, most likely due to the underestimation of measurement uncertainties. This underestimation was revealed and indirectly quantified using the Mandel-Paule method, which provides the interlaboratory uncertainty. The results from the presented comparison allow the present state of the BRDF scale realization to be evaluated, not only for classical in-plane geometries, but also for out-of-plane geometries.

En este trabajo se propone una escala de medida para la BSSRDF (Bidirectional Scattering-Surface Reflectance Distribution Function), una función que describe la variación de la radiancia de las áreas elementales de una superficie respecto al flujo radiante direccionalmente incidente en esa superficie. Medidas de esta función son importantes para caracterizar la translucidez de un objeto y para obtener las propiedades ópticas que afectan al esparcimiento o scattering en el volumen de este. En el Instituto de Óptica del CSIC (IO-CSIC) se ha desarrollado un sistema capaz de medir la BSSRDF de muestras translúcidas homogéneas y expresarla en unidades del SI. Debido a la inexistencia de experimentos anteriores acerca de la realización de la escala de la BSSRDF, en el presente trabajo se proponen tanto una serie de muestras que, posteriormente, puedan funcionar como patrones, como una serie de geometrías específicas de medida para esta magnitud.

Se presentan los resultados obtenidos de la medida de la BRDF (Bidirectional Reflectance Distribution Function) espectral de tres muestras translúcidas con distintas áreas de iluminación. Como ya se demostró en un trabajo anterior, se corrobora la dependencia de la BRDF con el área de iluminación y se relaciona esta variación con la longitud de onda para observar la consecuente diferencia en el color medido con las diferentes áreas de iluminación. Este trabajo advierte sobre la necesidad de establecer unas condiciones de medida del color en materiales translúcidos, en los que el color no solo está determinado por la reflectancia espectral de su superficie, sino también por la luz que emerge del volumen del material por efecto del esparcimiento (scattering).

Modern studies of bidirectional reflectance distribution function (BRDF) and its applications using data and machine-driven science require formatting of BRDF data according to Findable, accessible, interoperable and reusable (FAIR) data principles. As a solution a FAIR universal BRDF file-format based on Java Script Object Notation (JSON) is proposed. JSON principles as well as file structure are explained and examples are given. Automatic validation of universal BRDF file format is realized with the help of JSON schema. Furthermore, the source code and accompanying documentation are presented in dedicated supporting material files. It is expected that after its wide adoption, the proposed BRDF file format will enhance collaboration between different research groups and benefit machine-driven science. The uptake is facilitated by introducing a BiRDview—a modern open-source web-based application for BRDF visualization.

We consider theoretically an electronic Mach-Zehnder interferometer constructed from quantum Hall edge channels and quantum point contacts, fed with single electrons from a dynamic quantum dot source. By considering the energy dependence of the edge-channel guide centers, we give an account of the phase averaging in this setup that is particularly relevant for the short, high-energy wave packets injected by this type of electron source. We present both analytic and numerical results for the energy-dependent arrival time distributions of the electrons and also give an analysis of the delay times associated with the quantum point contacts and their effects on the interference patterns. A key finding is that, contrary to expectation, maximum visibility requires the interferometer arms to be different in length, with an offset of up to a micron for typical parameters. By designing interferometers that incorporate this asymmetry in their geometry, phase-averaging effects can be overcome such that visibility is only limited by other incoherent mechanisms.

This work presents a facility for measuring the Bidirectional Scattering-Surface Reflectance Distribution Function (BSSRDF), a function that describes the scattering of the light in translucent materials. This facility targets an expanded uncertainty of 5 %. The BSSRDF of twelve homogeneous and translucent samples has been measured to test the system and some results are represented here.

We report new developments in instrumentation and techniques for both acoustic (speed of sound) and radiometric primary thermometry methods. These include both new cylindrical resonators for extending acoustic gas thermometry to higher temperatures and absolute radiation thermometers incorporating InGaAs detectors to extend primary radiometry to lower temperatures than can be achieved using Si-detector based instruments. These new approaches have been established in order to determine the difference between thermodynamic temperature, T, and the International Temperature Scale of 1990 (the ITS-90), T90, over the temperature range from 430 K to 1358 K as part of the three-year EMPIR project `Implementing the new kelvin 2¿ (InK2). This paper describes the facilities and measurement methodologies for measuring T¿T90 at each of the different institutes, along with an assessment of the target uncertainties. The work is ongoing, but we anticipate that the results of these measurements will ultimately be pooled to provide consensus values of T¿T90 with associated estimated uncertainties. These consensus values will initially feed into the technical annex of the mise en pratique for the definition of the kelvin (MeP-K-19) and, if required, will be used to help to provide a foundation for any future temperature scale.

The dependence of color differences on the illumination and viewing directions for two widely used gray scales for color change (SDCE and AATCC) was evaluated through measuring the spectral bidirectional reflectance distribution function (BRDF) by a gonio-spectrophotometer of metrological quality. Large incidence and viewing angles must be specially avoided using these gray scales because, in these conditions, color differences vary considerably from those established in ISO 105-A02 and ASTMD2616-12. While the visual appearance of the SDCE and AATCC gray scales for color change is similar, our results indicate that their goniochromatic properties are different. Finally, some recommendations regarding observation distance and illumination angle are given to correctly use these gray scales for visual experiments.

The Bidirectional Reflectance Distribution Function (BRDF) of iridescent (or goniochromatic) surfaces may vary notably with both spectral and angular variables, and, therefore, finite spectral bandwidth and collection solid angles inherent to any measuring instrument introduce a deviation from the correct value. Experimental data of highly goniochromatic samples are used to analyse their impact on measurement uncertainty. The results indicate that it is advisable to standardize spectral and angular bandwidths because the systematic error is not negligible for typical measuring systems. The 95th percentile of the error distribution of the measurement of the BRDF due to these finite bandwidths, and also the 95th percentile of the calculated resulting color differences, are used as criteria to establish recommended values of spectral and angular bandwidths. The impact of the bandwidth is more critical in the measurement of the BRDF of diffraction-based than of interference-based coatings.

When measuring the Bidirectional Reflectance Distribution Function (BRDF) to characterize typical materials, the effect of the polarization of the light source or the dependence of the detector on the polarization is not usually considered, even though many studies have proven their impact in the uncertainty of the BRDF of most materials, including diffuse reflectance standards. A methodology to assess polarization-related effects proposed by other authors has been tested in this work for the measurement of the BRDF of four typical materials used for realizing white diffuse reflectance standards (ceramic tile, barium sulfate, Spectralon and Russian opal glass). Relative systematic error due to polarizing conditions is calculated as a combination of the instrument polarization bias and sample-based coefficients, and the impact of the proposed methodology on the uncertainty is discussed.

The bidirectional reflectance distribution function (BRDF) and the bidirectional scattering - surface reflectance distribution function (BSSRDF), which relate radiance at the surface to irradiance and radiant flux, respectively, are regarded as the most fundamental scattering quantities used to determine the reflectance of objects. However, for materials where the optical radiation is transmitted under the surface, this radiance depends not only on irradiance and radiant flux, but also on the size of the irradiated area of the surface. This article provides insight into such dependence under the special condition in which the radiance is evaluated within the irradiated area and, consequently, is produced by both the insurface reflection and the subsurface scattering, in contrast to the situation in which the radiance is evaluated at non-irradiated areas and only subsurface scattering contributes. By explicitly considering both contributions, two other scattering quantities are defined: one that accounts exclusively for the insurface reflection and the other that accounts for subsurface scattering. In this regard, these quantities might be considered more fundamental than the BRDF and the BSSRDF, although they are coincident with these two functions apart from the above-mentioned special condition and for materials with negligible subsurface scattering. In this work, the relevance of the proposed scattering quantities is supported by experimental data, practical considerations are given for measuring them, and their relation to the bidirectional transmittance distribution function (BTDF) is discussed.

The assumption that the reflectance of white diffuse reflectance standards is identical to that of the perfect reflecting diffuser (PRD) allows these standards to be used to characterize reflectance or radiance factors of any surface at any irradiation/collection geometry simply by comparison. However, this assumption is only true within certain limits, and, for some applications, requirements may be out of those limits. PTB and IO-CSIC have studied the variation of the reflectance with respect to the bidirectional geometry for the four most typical white diffuse materials (barium sulfate, opal glass, ceramic and Spectralon), at in- A nd out-of plane geometries and at spectral range from 380 nm to 1700 nm. We have defined descriptors in order to more clearly quantify the spectral reflectance variation with the bidirectional geometries. The values obtained for these descriptors have been separately presented for the visible and near-infrared spectral ranges. In both spectral ranges, deviations of white diffuse reflectance standards with respect to the PRD were found, regarding both Lambertian behaviour and spectral constancy. The observed deviation from the BRDF is in general very large for high incidence and collection angles (reaching in many cases 20%). Therefore, it is not possible to assume Lambertianity in standards at those geometries when calibrating measuring systems.

Therefore, the aim of this work is to build a complete rendered simulation of the Byko-spectra effect lightbooth. This simulated light booth will be used in the next phase of this work, to support psychophysical visual experiments on the rendering of virtual objects inside the virtual lightbooth and real samples inside the physical lightbooth to improve the visualization of 3D objects covered by effect coatings.

Research project “Future photometry based on solid-state lighting products” (EMPIR 15SIB07 PhotoLED) has investigated the fundamental requirements for photometry based on white lightemitting diode (LED) sources. The project has developed new LED illuminants, LED standard lamps for luminous intensity and luminous flux, as well as new photometric measurement methods, addressing many technical challenges of the CIE research strategy. In this paper, we present the outcome of the 3-year scientific research project, whose work has been carried out by NMIs, universities, test laboratories and industrial partners working in the field of photometry and solid-state lighting.

Photometric calibrations are mainly based on the use of scientific grade incandescent standard lamps [CIE 2002]. Most of the measurement methods and reference spectra used in photometry were developed long before modern solid-state lighting (SSL) products were invented and introduced into the lighting market. In addition, phasing-out of incandescent lamps for lighting applications poses a metrological problem: all lamps and luminaires measured in practice differ completely in their behaviour with respect to spectral distribution, flicker and aging, as compared to incandescent lamps used in photometer calibrations. The European research project “Future photometry based on solid-state lighting products” (EMPIR 15SIB07 PhotoLED) has investigated the fundamental requirements for photometry based on white light-emitting diode (LED) sources. The project partners have analysed many hundreds of LED spectra and derived suitable LED reference spectra for photometric calibrations. In this article we present the practical advantages and disadvantages of luminous intensity standards based on white LEDs with very similar spectra to the hypothetical reference spectrum developed in the project. Furthermore, we discuss their suitability for metrological comparisons of the luminous intensity.

The technical committee TC 2-90 (“LED Reference spectrum for photometer calibration”) has been recently created by CIE to investigate, select and publish an LED Reference spectrum to complement the CIE Standard Illuminant A in photometric calibrations. This task additionally requires defining a spectral mismatch index to account for the match of spectral power distributions (SPDs) of real sources to the selected reference spectrum. The objective of this work is to propose such a spectral mismatch index, and to evaluate its performance using real and representative LED spectral power distributions and relative spectral responsivities of photometers.

The digital representation of three dimensional objects with different materials has become common not only in the games and movie industry, but also in designer software, e-commerce and other applications. Although the rendered images often seem to be realistic, a closer look reveals that their color accuracy is often insufficient for critical applications. Storage of the angledependent color properties of metallic coatings and other gonioapparent materials demands large amounts of data. Apart from that, also rendering sparkle, gloss and other visual texture phenomena is still a subject of active research. Current approaches are computationally very demanding, and require manual ad-hoc setting of many model parameters. In this paper, we describe a new approach to solve these problems. We combine a multi-spectral physics-based approach to make BRDF representation more efficient. We also account for the common loss in color accuracy due to the varying technical specifications of displays, and we correct for the influence from ambient lighting. The rendering framework presented here is shown to be capable of rendering sparkle and gloss as well, based on objective measurement of these properties. This takes out the subjective phase of manual fine-tuning of model parameters that is characteristic for many current rendering approaches. A feasibility test with the new spectral rendering pipeline shows that is indeed able to produce realistic rendering of color, sparkle, gloss and other texture aspects. The computation time is small enough to make the rendering real-time on an iPad 2017, i.e. with low memory footprint and without high demands on graphic card or data storage.

In this paper, the fisheye camera method is validated for spatial non-uniformity corrections in luminous flux measurements with integrating spheres. The method was tested in eight integrating spheres with six LED lamps, and the determined angular intensity distributions and spatial non-uniformity correction factors were compared with the results of five goniophotometers. The average closeness score, describing the similarity between any two distributions, was 94.6 out of 100 for the distributions obtained using the fisheye camera method when compared with the goniophotometric results. The average closeness score for the five goniophotometers, when each goniophotometer was compared with the other four, was 96.6. On average, the relative deviation between the two methods was 0.05% when calculating the spatial corrections. The most significant sources of uncertainty for the fisheye camera method were large, view-obstructing sphere elements residing close to the camera port.

High-performance optical beam splitters are of fundamental importance for the development of advanced silicon photonics integrated circuits. However, due to the high refractive index contrast of silicon-on-insulator platforms, state-of-the-art nanophotonic splitters are hampered by trade-offs in bandwidth, polarization dependence and sensitivity to fabrication errors. Here, we present a new strategy that exploits modal engineering in slotted waveguides to overcome these limitations, enabling ultra-broadband polarization-insensitive optical power splitters with relaxed fabrication tolerances. The proposed splitter design relies on a single-mode slot waveguide that is gradually transformed into two strip waveguides by a symmetric taper, yielding equal power splitting. Based on this concept, we experimentally demonstrate −3 ± 0.5 dB polarization-independent transmission for an unprecedented 390 nm bandwidth (1260–1650 nm), even in the presence of waveguide width deviations as large as ±25 nm.

After measuring thermodynamic temperatures in the range from 900 °C to 2500 °C, The Centro Español de Metrologia (CEM) in collaboration with the Instituto de Óptica of the Consejo Superior de Investigaciones Científicas (IO-CSIC) are currently involved in the measurement of thermodynamic temperatures down to 400 °C using radiometers based on InGaAs detectors with central wavelengths in the near-infrared spectral range (NIR). This communication summarizes the progress towards the extension of absolute radiation thermometry measurement range to lower temperatures. © 2018 Institute of Physics Publishing. All rights reserved.

Determining reflectance factor and its variability across reference sites for Earth observation satellites is a problem involving large amounts of data and measurement time. Principal component analysis (PCA) may be used to simplify this problem by reducing the size of the data and by highlighting spectral features that could be related to physical phenomena. This work presents the results obtained in applying PCA to two reference sites for calibration and validation of Earth observation satellites located at La Crau (France) and Gobabeb (Namibia), respectively.

Effect pigments in coatings produce eye-catching colour and texture effects and are widely used in automotive, cosmetics, coatings, inks, flooring, textile or decoration. One of these texture effects is graininess, which is the perceived texture exhibited when the effect coating is observed under diffuse illumination. To date there is not a standard procedure to measure graininess from reflectance measurements. The objective of this work is to propose a methodology for traceable graininess measurements, similarly as it was proposed for colour in 1931. In this article, the relevant reflectance-based quantities are clearly defined, and a formal relation with data from visual experiments is given. This methodology would allow a measurement scale of graininess and a difference formula to be agreed once conclusive visual data become available.

This paper describes a technique to perform traceable temperature measurements of the seawater column and seawater surface, based on optical fiber Bragg gratings. The paper explains the different phases of the work done: design of the optical fibers, its optical and thermal calibration and onsite measurements of the seawater temperature. In the design of these thermometers, special attention was paid to the involved materials in order to prevent any damage of the fibers due to the exposure to such rugged environment. The fibers were subjected to optical and thermal calibration, with the aim to get traceable measurements and reliable uncertainty calculation of the seawater temperature. The fibers were deployed in the Mediterranean Sea and water temperatures were continuously monitored and compared with the most common used thermometer in this environment, CTD, located in the submarine observatory OBSEA.

Numerical simulations are the common method to predict the response of a quantum efficient detector of induced-junction photodiodes at present. As alternative, an analytical model based on Ferrero et al. photocurrent analysis is proposed. Surface and bulk losses are modelled considering design and operation photodiode parameters and the characteristics of the incident beam. At short wavelengths the surface recombination velocity dominates the losses, whereas the bulk doping and reverse bias voltage determine the losses at long wavelengths. The losses predicted by the analytical model and reported simulations by other authors are in the same order of magnitude between 400 nm and 700 nm.

We present two techniques for mitigating the effects of temperature drifts in waveguide spatial heterodyne Fourier-transform on-chip spectrometers. In high-resolution devices, large optical path length differences result in an increased sensitivity to temperature variations and impose stringent requirements on the thermal stabilization system. In order to overcome this limitation, here we experimentally demonstrate two new temperature mitigation techniques based on a temperature-sensitive calibration and phase error correction. The spectrometer chip under analysis comprises an array of 32 Mach¿Zehnder interferometers fabricated on a silicon-on-insulator platform. The optical path delays are implemented as microphotonic spirals of linearly increasing length up to 3.779 cm, yielding a spectral resolution of 17 pm. We demonstrate that the degradation in retrieved spectra caused by temperature drift is effectively eliminated by temperature-sensitive calibration and phase error correction.

CIELAB color coordinates are characteristics of visible object¿s spectra widely used in color science, and a reliable evaluation of the uncertainty associated with measured color coordinates is desirable. The calculation of CIELAB color coordinates requires the application of a nonlinear transformation. We consider two ways to calculate the uncertainty of CIELAB color coordinates that originates from the uncertainty of the observed spectrum. The ¿rst approach is based on a linearization of the nonlinear transformation and a propagation of variances and covariances. The second approach is a Monte Carlo procedure that completely accounts for the nonlinearity of the trans- formation. While the approach based on linearization results in analytical formulas, the adequacy of linearization ought to be checked and the proposed Monte Carlo method can serve as a reference method for this purpose. We illustrate such proceed- ing in a large range of scenarios and explore those cases for which the method based on linearization may safely be applied.

Embedding optical fibers sensors into composite structures for Structural Health Monitoring purposes is not just one of the most attractive solutions contributing to smart structures, but also the optimum integration approach that insures maximum protection and integrity of the fibers. Nevertheless this intended integration level still remains an industrial challenge since today there is no mature integration process in composite plants matching all necessary requirements. This article describes the process developed to integrate optical fiber sensors in the Production cycle of a test specimen. The sensors, Bragg gratings, were integrated into the laminate during automatic tape lay-up and also by a secondary bonding process, both in the Airbus Composite Plant. The test specimen, completely representative of the root joint of the lower wing cover of a real aircraft, is comprised of a structural skin panel with the associated stringer run out. The ingress-egress was achieved through the precise design and integration of miniaturized optical connectors compatible with the manufacturing conditions and operational test requirements. After production, the specimen was trimmed, assembled and bolted to metallic plates to represent the real triform and buttstrap, and eventually installed into the structural test rig. The interrogation of the sensors proves the effectiveness of the integration process; the analysis of the strain results demonstrate the good correlation between fiber sensors and electrical gauges in those locations where they are installed nearby, and the curvature and load transfer analysis in the bolted stringer run out area enable demonstration of the consistency of the fiber sensors measurements. In conclusion, this work presents strong evidence of the performance of embedded optical sensors for structural health monitoring purposes, where in addition and most importantly, the fibers were integrated in a real production environment and the ingress-egress i

The field of spectral radiance factor (SRF) measurements has seen growing interest in recent years. Scale conformity has so far only been established between the national metrology institutes (NMIs) of Germany and the USA. This study aims at a bigger, multilateral scale comparison. For this purpose, a total of six NMIs participated in a scale comparison of goniospectrophotometers based on neutral and colored diffusely reflecting ceramics samples. In addition, two universities, providing a home-built gonioreflectometer and two widely used commercially available color measurement instruments, respectively, were involved. The wavelength range of the scale comparison covers the visible wavelength range from 380 nm to 780 nm. Results indicate systematic issues and that the uncertainty evaluation of the NMIs requires further work; although for the greatest part of the covered spectral range the agreement is good.

The potential of predictable quantum efficient detectors (PQEDs) as optical radiant power primary standard, based on photoelectric effect in silicon semiconductor, has been proved. Until now, the internal quantum efficiency (IQE) of a PQED is only predicted, from the design and setup parameters of the two photodiodes of this radiometer, by means of simulation software for semiconductor devices. This work presents, as alternative method, an analytical model based on Ferrero et al. photocurrent analysis, which considers the different internal regions of the photodiode and the characteristics of the incident beam. The IQE grows with the reverse bias voltage applied to the photodiodes and the lifetime of the charge carriers in the bulk, while IQE decreases when the surface recombination velocity and the doping concentration of the substrate are increased. The IQE results of the analytical model are similar to simulations for wavelengths between 400 nm and 700 nm. Moreover, the analytical model predicts an increase of the IQE with the irradiance, at certain levels of optical power due to the supra-responsivity of the photodiode.

The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488¿nm and 532¿nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30¿ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs

In the textile industry, grey scales for colour change are used in fastness tests. These scales consist of nine pairs of neutral grey chips representing a visual colour difference corresponding to fastness ratings from 5 (no contrast) to 1 (highest contrast). The dependence of colour differences on the illumination and viewing directions for two widely-used grey scales (“Grey Scale for Assessing Change in Colour” (SDCE), and “Gray Scale for Evaluating Change in Color” (AATCC)) was evaluated. The spectral bidirectional reflectance distribution function (BRDF) was measured at a set of geometries well distributed in the observation domain, using the goniospectrophotometer GEFE developed at CSIC. It was found that large incidence and viewing angles must be specially avoided using these scales, as providing colour difference values considerably different than those established in ISO 105-A02 and ASTM D2616-96.

A RGB LED mosaic source was examined as a test standard source to estimate the most important quality indices of Imaging Luminance Measurement Devices (ILMDs), such as general V(¿) mismatch index f1¿, stray light influence for negative contrast, edge function, size-of-source ffect, effect of the surrounding field, linearity for a luminance range, non-uniformity and smear. Reproducibility of the emission of the mosaic source, its uniformity and its spectral distribution was characterized for this purpose. The methods to estimate different quality indices of ILMDs are described.

Following the strategy in a previous work, we have evaluated the potential Blue-Light Hazard (BLH) of high colour rendering index LED sources, on people whose crystalline lenses have been removed through a surgical procedure to implant intraocular lenses. Starting from the spectral transmittance of various models of commercial intraocular lenses (IOLs), modifications of the action spectrum for the BLH photo biological effect are proposed for each type of IOL. Then, using the corrected action spectra, the potential hazard of different types of white LED sources on subjects implanted with those IOLs, as compared to the potential hazard of the same sources for a person whose crystalline lens has not been removed, has been calculated.

Determining reflectance factor and its variability across calibration sites for Earth observation satellites is a problem involving a large number of data. Principal components analysis (PCA) may be used to simplify this problem by reducing the number of data and by highlighting spectral features that could be related to physical phenomena. This work presents the results obtained in applying PCA to two calibration sites in La Craux (France) and Gobabeb (Namibia).

Solid-state lighting (SSL) products are already in use by consumers and are rapidly gaining the lighting market. Especially, white Light Emitting Diode (LED) sources are replacing banned incandescent lamps and other lighting technologies in most general lighting applications. The aim of this work is to develop LED-based illuminants that describe typical white LED products based on their Spectral Power Distributions (SPDs). Some of these new illuminants will be recommended in the update of the CIE publication 15 on colorimetry wi th the other typical illuminants, and among them, some could be used to complement the CIE standard illuminant A for calibration use in photometry.

Comparison of the reflectance properties of different diffuse reflectance standards provides guide to select the standard most adequate for a given application. IO-CSIC and PTB have studied the variation of the spectral BRDF with respect to the standard bidirectional geometry 0º:45º of the four most typical diffuse reflectance standards (barium sulphate, opal glass, ceramic tile and Spectralon), within the spectral range [380-1700] nm. IO-CSIC measured the variation in-plane spectral BRDF at several incidence angles, whereas PTB measured its out-ouf-plane variation at a fixed 45º incidence angle.

New methods to characterize coatings with effect pigments are necessary to quantify their complex appearance. A description of the challenges faced by their characterization is given in this contribution.

La caracterización colorimétrica de diferentes materiales es un objetivo prioritario en muchos sectores, tanto de investigación como industriales. Cuando estos materiales muestran características especiales, como los materiales gonioaparentes, o aquellos que presentan cierta textura, las técnicas de caracterización colorimétrica empiezan a revestir cierta dificultad, puesto que el control sobre el ángulo de iluminación y observación es determinante para dicha caracterización. En particular, con los colores fluorescentes hay una dificultad añadida, puesto que la complicación radica en el hecho de que estos materiales no sólo reflejan parte de la luz que les llega, sino que además emiten radiación en longitudes de onda diferentes a las que han sido irradiadas. Por ello, no sólo entra en juego la geometría de la iluminación/observación, sino que además es especialmente importante controlar la longitud de onda UV-VIS con la que se ilumina y observa dicha muestra. Aunque en la actualidad hay diferentes instrumentos que son capaces de medir la fluorescencia, y en términos relativos para numerosas aplicaciones, no es habitual encontrarlos bien caracterizados y calibrados para colorimetría pese a existir normativas específicas relativa a estas medidas especiales tanto por parte de la CIE [1], como por parte de organismos de estandarización como ASTM [2, 3]. Se describe aquí cómo se usó un espectrofluorímetro modular adquirido por el Grupo de Visión y Color de la Universidad de Alicante para la caracterización colorimétrica de materiales fluorescentes.

We propose a method based on Zernike polynomials to characterize photometric quantities and descriptors of light emitting diodes (LEDs) from measurements of the angular distribution of the luminous intensity, such as total luminous flux, BA, inhomogeneity, anisotropy, direction of the optical axis and Lambertianity of the source. The performance of this method was experimentally tested for 18 high-power LEDs from different manufacturers and with different photometric characteristics. A small set of Zernike coefficients can be used to calculate all the mentioned photometric quantities and descriptors. For applications not requiring a great accuracy such as those of lighting design, the angular distribution of the luminous intensity of most of the studied LEDs can be interpolated with only two Zernike polynomials. © 2016 IOP Publishing Ltd

The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature. © 2016 The Author(s)

Coatings with diffraction pigments present high iridescence, which needs to be characterized in order to describe their appearance. The spectral bidirectional reflectance distribution functions (BRDFs) of six coatings with SpectraFlair diffraction pigments were measured using the robot-arm-based goniospectrophotometer GEFE, designed and developed at CSIC. Principal component analysis has been applied to study the coatings of BRDF data. From data evaluation and based on theoretical considerations, we propose a relevant geometric factor to study the spectral reflectance and color gamut variation of coatings with diffraction pigments. At fixed values of this geometric factor, the spectral BRDF component due to diffraction is almost constant. Commercially available portable goniospectrophotometers, extensively used in several industries (automotive and others), should be provided with more aspecular measurement angles to characterize the complex reflectance of goniochromatic coatings based on diffraction pigments, but they would not require either more than one irradiation angle or additional out-of-plane geometries. © 2016 Optical Society of America

In this work, we analyze the effect of temperature drifts in a spatial heterodyne Fourier-transform micro-spectrometer fabricated in a Silicon-on-insulator chip. The device comprises an array of 32 Mach-Zehnder interferometers implemented with microphotonic spirals of linearly increasing length. This configuration provides a resolution of 42 pm in a footprint under 12 mm. However, this resolution enhancement implies a greater sensitivity to environmental variations during the spectrometer operation. In this work, the effect of temperature drifts in the spectral retrieval algorithm is studied, and compensation techniques based on multiple calibration matrices is presented. © Sociedad Española de Óptica

The goniospectrophotometer GEFE, designed and developed at IO¿CSIC (Instituto de ¿ Optica, Agencia Estatal Consejo Superior de Investigaciones Cient¿¿ficas), was conceived to measure the spectral Bidirectional Reflectance Distribution Function (BRDF) at any pair of irradiation and detection directions. Although the potential of this instrument has largely been proved, it still required to be upgraded to deal with some important scattering features for the assessment of the appearance. Since it was not provided with a detector with spatial resolution, it simply could not measure spectrophotometric quantites to characterize texture through the Bidirectional Texture Function (BTF) or translucency through the more complex Bidirectional Scattering¿Surface Reflectance Distribution Function (BSSRDF). Another requirement in the GEFE upgrading was to provide it with the capability of measuring fluorescence at different geometries, since some of the new pigments used in industry are fluorescent, which can have a non¿negligible impact in the color of the product. Then, spectral resolution at irradiation and detection had to be available in GEFE. This paper describes the upgrading of the goniospectrophotometer GEFE, and its new capabilities through the presentation of sparkle and goniofluorescence measurements. In addition, the potential of the instrument to evaluate translucency by the measurement of the BSSRDF is briefly discussed.

El comportamiento lineal en la respuesta de un fotodiodo es una condición fundamental en medidas radiométricas, espectrofotométricas y de radiación pulsada o continua. Por tanto, se requiere que la respuesta eléctrica del fotodiodo sea proporcional al flujo radiante incidente y que se mantenga estable en el tiempo y en un rango de irradiancia. Sin embargo, diversas medidas publicadas evidencian una falta de linealidad dependiente de la estructura interna del fotodiodo, de la potencia y del tamaño del haz incidente. Este trabajo, para caracterizar la no-linealidad en la respuesta de fotodiodos como función de estos mismos factores, adopta el modelo de eficiencia cuántica interna desarrollado por Ferrero et al. en el Instituto de Óptica (CSIC). Además, mediante simulaciones para distintos supuestos, evalúa la influencia de cada parámetro en la no-linealidad de respuesta comparando resultados de las simulaciones con datos experimentales seleccionados en una recopilación bibliográfica.

In an effort to create more dynamic looking automobiles, there is an ever increasing trend among automobile manufacturers towards the use of gonio-apparent coatings in car bodies. These coatings consist of transparent pigments mixed with metallic or interference flakes. The flakes in the coating cause a change in color and brightness of the finish with viewing and illumination direction. This change in appearance accentuates the 3D shading of a car body, making it visually more attractive. Besides this angular dependence on viewing/illumination direction, the metallic finishes also exhibit a visually complex texture. Depending on the properties of the finish and the viewing and illumination conditions, the flakes exhibit a sparkle like texture, while the glossy clear coat may show a rough or smooth surface. As a result of these complex visual attributes, capturing the appearance and finding a perfect color match for an automotive coating is a non trivial task. The main objective of this work is to evaluate the relationship between the special-effect pigments size, and the maximum distance which is detectable the sparkle texture effect. For this, two different sets of samples with different structural features were evaluated in a lighting booth specifically designed for the visual experiment. The booth allows to vary the lighting conditions, the viewing geometry and the distance at which the sample is perceived. The visual experiment was applied to evaluate the high correlation between a structural parameter (i.e. pigment size) and the visual appearance attribute related with texture (sparkle detection distance). Under some fixed environmental conditions, as light intensity, color temperature and geometry of the light source, the sparkle detection distance was evaluated by applying the adjustment psychophysical method for two panel sets (metallic grays and blues), with known pigment sizes and colorimetry, with a small set of observers. The visual results show that a

The lighting industry has experienced a revolution with the arrival of novel lighting technologies in particular Light Emitting Diodes. LEDs have clear advantages in energy efficiency over conventional lighting technologies, and since 19 % of electricity worldwide is used for lighting, this can contribute significantly to saving energy problems worldwide and contributing to Europe¿s 2020 strategy. In order to validate performance claims and stimulate user confidence, as well as facilitate efficient development of this kind of products, dedicated metrology is needed. The objective of this work was to study goniometrical aspects of LEDs, and their dependence with distance to find a model to predict the illuminance at any distance. A modified inverse-square law model, considering only the offset of the LED virtual source with respect to their front tip is proposed. The applicability of the method was tested for 18 LED¿s types, with different angular and spectral distributions.