Suchergebnisse

11 pags., 5 figs. ; The General V(λ) Mismatch Index, f, was defined for a general description of the photometric performance of photometers. This index is widely-used in photometry, and it is very relevant for selecting photometers for low-uncertainty photometric measurements. It quantifies the spectral mismatch between the relative spectral responsivity of a photometer and the luminous e ciency function for photopic vision, V(λ). The linear correlation between the real general photometric measurement error and f of 77 photometers was studied for four sets of light sources: R, G and B LEDs (narrowband spectral power distributions, SPDs), blackbodies at di erent colour temperatures (broadband SPDs), phosphor-based LEDs at di erent correlated color temperatures (SPDs with narrow- and broad-band features), and a mixture of blackbodies and phosphor-based LED sources. This article shows that it can be defined an alternative index which is notably better correlated with the real general photometric measurement error of the photometers under light sources with broadband features in their SPDs, adequate for general lighting. This index is based on filtering the high spectral frequencies variations between the relative spectral responsivity of the photometer and V(λ). The use of this new index for the assessment of the general photometric performance of photometers would improve the selection of high quality photometers and, consequently, would contribute to the general improvement of photometric measurements. ; EURAMET and the European Union (15SIB07); Comunidad de Madrid (S2013/MIT-2790).

8 pags., 7 figs., 3 tabs.-- Parts of this work have been presented at XI Reunión Nacional de Óptica in Self-calibration of silicon photodiodes internal quantum efficiency by using temperature sensors, 2015. ; Predictable quantum efficient detectors (PQEDs), based on photoelectric effect in silicon semiconductor, have proved their potential as optical radiant power primary standard. At present, simulations for semiconductor devices are the common method to predict the response of a PQED. As an alternative, this work investigates the feasibility of an experimental technique, the self-calibration of silicon photodiodes at room temperature by means of temperature sensors. A device which compares two physics principles by optical power, working both as a photodetector and a radiometer based on electrical substitution, was made. The device allows for measuring the current generated under irradiation (in photocurrent mode) and the heating of the system, induced by a laser or forward biasing, to determine the optical power (in thermal mode). The feasibility study consists of testing the equivalence between both modes and establishing the suitable range of optical power. The range of optimum optical power level, where both modes run in the linear domain at the present configuration, is from 300 μW up to 1 mW. Within this range, the optical power experimental uncertainty is lower than 1%. ; This work has been supported by the European Commission through the project SIB57-NEWSTAR under the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. The authors of CSIC acknowledge support from the Comunidad de Madrid and the European Union under program SINFOTON-CM (S2013/MIT-2790). ; Peer Reviewed

9 págs.; 6 figs.; 4 tabs. ; 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 ; This work was accomplished within the EMRP ENG05 Project 'Metrology for Solid State Lighting'. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. The authors are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790. ; Peer Reviewed

Proceedings of SPIE 9398; San Francisco, California, United States | February 8-9, 2015 ; 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. ; Authors are grateful to EMRP for funding the project "Multidimensional reflectometry for industry". The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Authors are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790. ; Peer Reviewed

8 pags., 7 figs., 1 tab. ; 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. ; To the European Metrology Research Program (EMRP), supporter of this work within the joint research project ENV53 "European metrology for Earth observation and climate" (MetEOC2). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We thank CNES for access to La Crau and their support with the measurements at both La Crau and Gobabeb. The IO-CSIC authors are also grateful to Comunidad de Madrid for funding the program SINFOTON-CM: S2013/MIT-2790

10 pags., 8 figs., 3 tabs.-- Open Access funded by Creative Commons Atribution Licence 3.0 ; 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. ; This article was written within the EMRP IND52 Project xDReflect 'Multidimensional reflectometry for industry'. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica 'Daza de Valdés', CSIC) are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790.

7 págs., 7 figs., 1 tab. -- ; 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 work leading to this study is partly funded by the European Metrology Programme for Innovation and Research (EMPIR) Project 15SIB07 PhotoLED 'Future Photometry Based on Solid State Lighting Products'. The EMPIR initiative is cofunded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

7 págs., 7 figs., 1 tab. ; 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 work leading to this study is partly funded by the European Metrology Programme for Innovation and Research (EMPIR) Project 15SIB07 PhotoLED 'Future Photometry Based on Solid State Lighting Products'. The EMPIR initiative is cofunded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

Timo Dönsberg et al. -- 16 pags., 16 figs., 4 tabs. -- Open Access funded by Creative Commons Atribution Licence 3.0 ; 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 is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers. ; The research leading to these results has received funding from the European Metrology Research Programme (EMRP) project SIB57 'New Primary Standards and Traceability for Radiometry'. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Financial support from the Academy of Finland through the Finnish Centre of Excellence in Atomic Layer Deposition is also acknowledged. ; Peer Reviewed

9 pags., 5 figs., 1 tab. ; 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. ; This work has been supported by the European Commission through the project SIB57-NEWSTAR under the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. The authors of CSIC acknowledge support from the Comunidad de Madrid and the European Union under program SINFOTON-CM (S2013/MIT-2790). ; Peer Reviewed

8 págs.; 7 figs. ; The spectral bidirectional reflectance distribution function (BRDF) is the key quantity to specify the spectral reflectance of materials for any condition of irradiation and detection, and its characterization is quite important for surfaces with a high dependence on these conditions, such as iridescent coatings. In order to evaluate the calibration and measurement capabilities (CMC) of National Metrology Institutes with the ability to measure the spectral BRDF, a case study interlaboratory comparison is in progress. Spectral BRDF has both spectral and geometric dependence, and this multidimensionality must be treated in the comparison to provide useful information to the participants about their CMCs. A data analysis method for the comparison is presented in this work, which was tested by simulations for different scenarios. The proposed method assesses whether the experimental data from each participant are consistent with those from the others. Finally, one-dimensional and multidimensional degrees of equivalence are defined, which should allow systematic deviations of spectral and geometric nature to be identified. ; This report was compiled within the EMRP IND52 Project xD-Reflect 'Multidimensional reflectometry for industry'. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica 'Daza de Valdés', Agencia Estatal CSIC) are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790. ; Peer Reviewed

A reduced set of measurement geometries allows the spectral reflectance of special effect coatings to be predicted for any other geometry. A physical model based on flake-related parameters has been used to determine nonredundant measurement geometries for the complete description of the spectral bidirectional reflectance distribution function (BRDF). The analysis of experimental spectral BRDF was carried out by means of principal component analysis. From this analysis, a set of nine measurement geometries was proposed to characterize special effect coatings. It was shown that, for two different special effect coatings, these geometries provide a good prediction of their complete color shift. ©2013 Optical Society of America. ; The authors are grateful to "Plan Nacional de Física"for funding this work (FIS2010-19756-E), to CSIC's JAE Program, and the "European Social Fund" for awarding us a research trainee. This study was also supported by the Spanish Ministry of Economy and Competitiveness under the grant DPI2011-30090-C02-02 and the European Union. ; Peer Reviewed

A representation of the color gamut of special effect coatings is proposed and shown for six different samples, whose colors were calculated from spectral bidirectional reflectance distribution function (BRDF) measurements at different geometries. The most important characteristic of the proposed representation is that it allows a straightforward understanding of the color shift to be done both in terms of conventional irradiation and viewing angles and in terms of flake-based parameters. A different line was proposed to assess the color shift of special effect coatings on a*,b*-diagrams: the absorption line. Similar to interference and aspecular lines (constant aspecular and irradiation angles, respectively), an absorption line is the locus of calculated color coordinates from measurement geometries with a fixed bistatic angle. The advantages of using the absorption lines to characterize the contributions to the spectral BRDF of the scattering at the absorption pigments and the reflection at interference pigments for different geometries are shown. ; The authors are grateful to the "Plan Nacional de Física" for funding this work FIS2010-19756-E, to CSIC's JAE Program, and the "European Social Fund" for awarding us a research grant. This study was also supported by the Spanish Ministry of Economy and Competitiveness under Grant No. DPI2011-30090-C02-02 and the European Union.

28th Session, Manchester/UK, June 28 - July 4, 2015; http://session2015.cie.co.at/ ; Fluorescent materials absorb light at a certain wavelength interval and then reemit it at other longer wavelengths, after about 10-8 seconds. Their colour appearance depends upon the combined effect of the fluorescent and reflected radiation. This work is focused in the measurement of the fluorescence of photolumiscent materials as a function of the irradiation and detection directions, which may be called as ¿goniofluorescence¿. It was measured the spectral bidirectional luminiscence distribution function (BLDF) of five fluorescent samples at different combinations of irradiation and detection directions. The measurements were performed with the goniospectrophotometer GEFE, using monochromatic irradiation and a spectrorradiometer as detector. A general behaviour was observed for the five samples and the studied excitation wavelengths: the dependence of the excitation spectrum on the detection direction ¿s is almost symmetrical with respect to ¿s = 0o, decreasing towards high angles. ; This report was compiled within the EMRP IND52 Project xD-Reflect "Multidimensional reflectometry for industry". The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica "Daza de Valdés" (IO-CSIC), Agencia Estatal CSIC) are also grateful to the Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790. ; Peer Reviewed

A reduced set of measurement geometries allows the spectral reflectance of special effect coatings to be predicted for any other geometry. A physical model based on flake-related parameters has been used to determine nonredundant measurement geometries for the complete description of the spectral bidirectional reflectance distribution function (BRDF). The analysis of experimental spectral BRDF was carried out by means of principal component analysis. From this analysis, a set of nine measurement geometries was proposed to characterize special effect coatings. It was shown that, for two different special effect coatings, these geometries provide a good prediction of their complete color shift. ; The authors are grateful to "Plan Nacional de Física" for funding this work (FIS2010-19756-E), to CSIC's JAE Program, and the "European Social Fund" for awarding us a research trainee. This study was also supported by the Spanish Ministry of Economy and Competitiveness under the grant DPI2011-30090-C02-02 and the European Union.