GONIOPHOTOMETER

This paper summarizes selected approaches, to generate spectral ray data for different types of spectrally varying light sources including only angular variable as well as spatial and angular variable sources. This includes a description of their general ideas and applications, the required measurements, and their mathematical concepts. Finally, achieved results for an Red/Green/Blue/White-light emitting diode (RGBW-LED) system are shown. Ray tracing simulations of a spatially and angularly spectral varying LED system combined with a spectrally sensitive optical system are qualitatively and quantitatively compared to a colorimetric far-field measurement of the same system. The results demonstrate the potential and benefits of spectral ray files in general.

Die Anforderungen an Lichtquellenmodelle im Entwurfsprozess moderner Leuchten für die allgemeine Lichttechnik nehmen im Zuge der steigenden Anforderungen an die Beleuchtungstechnik stetig zu. Dabei rückt zunehmend auch die ort- und winkelaufgelöste Farb- und Spektralverteilung in den Vordergrund. Basierend auf der Annahme, dass die spektrale Variation von Lichtquellen als gewichtete Summe von konstanten Basisspektren beschreibbar ist, soll in diesem Beitrag ein allgemeiner Messansatz zur Erzeugung solcher Lichtquellenmodelle vorgestellt werden Der Schwerpunkt liegt dabei auf der Messung und Rekonstruktion der spektralen Information. Des Weiteren wir das Verfahren auf Basis einer leuchtstoffbasierten Weißlicht-LED getestet und mit dem speziell auf diese LED-Familie zugeschnittenen Stand der Technik – dem Blau/Gelb Rayfile – vergleichen.

The enhanced complexity of modern lighting systems has increased the importance of realistic light source models during the optical design process of LED-based luminaires. I. Rotscholl, Research Associate, K. Trampert, C. Neumann, I. Leopoldo Sayanca from the Karlsruhe Institute of Technology, U. Krüger and F. Schmidt from the TechnoTeam Bildverarbeitung GmbH, propose a method to enhance the often used LED light source model “ray file” towards a “spectral ray file”. A spectral ray file would be a model that associates each ray with its own spectrum and therefore describes varying spectra as a function of angular direction and spatial starting position. The PMBS (physically motivated basis spectra) method is based on the assumption that each LED spectrum consists of a weighted sum of individual basis spectra, for instance, those of individual semiconductors and phosphors. There is no need for any special measurement equipment but a classic nearfield goniophotometer and some off-the-shelf optical filters. This method requires at least one spectral measurement and just a minimum of goniophotometric measurements with different optical filters. Finally, the authors demonstrate the potential of this method by applying the concept on a typical LED and compare the results to the often used Blue/Yellow approach in terms of accuracy and applicability.

The availability of accurate photometric data is crucial for the development of lighting technology components. Especially in the course of the displacement of the classical lamps by solid-state lighting (SSL) technologies and the resulting increased range of lighting applications, the requirements for these measurement data have increased. Here, optical simulation programs based on ray tracing algorithms (Computer-Aided Lighting – CAL) open up new development processes. State-of-the-art is the use of ray files measured by camera-based near-field goniophotometers. Some of those systems also offer measurements of the luminous intensity distribution, luminous flux and goniospectrometric data in conformity with IES LM-79-08, EN 13032-4 and CIE S 025, and can thus also take over the classical measurement tasks of far-field goniophotometers. This paper illustrates applications of the data measured with near-field goniophotometers and luminance measuring cameras in the field of simulation, glare evaluation and luminaire characterization.

This book presents, validates, and applies a fast, accurate and general measurement and modeling technique to obtain spectral near field data of LED systems for optical simulations in order to address the steadily increasing requirements of modern high-quality LED systems. It requires only a minimum of goniophotometric near field measurements and no time-consuming angularly resolved spectral measurements. The obtained results can be used directly in state-of-the-art ray tracers.

Solid State Lighting (SSL)-Leuchten (LED, OLED, PLED) stellen höhere Anforderungen an die photometrische Messtechnik. Kamerabasierte Goniophotometer (Nahfeldgoniophotometer) bieten hier wesentliche Vorteile gegenüber klassischen mit Einzelsensoren messenden Systemen (Fernfeldgoniophotometer) und sind auch für zukünftige erweiterte Messaufgaben gerüstet. Der folgende Beitrag erläutert beispielhaft erweiterte Möglichkeiten zur realitätskonformeren UGR-Blendungsbewertung und für Simulationen von Beleuchtungssituationen. Weiterhin wird die Thematik der für Fernfeldgoniophotometer relevanten photometrischen Grenzentfernung beleuchtet.

The measurement of the spectral power distribution (SPD) of a radiation source by array spectroradiometers is a technique that is widely used. In many applications, quantities that are derived from the SPD by a weighted integral over a wavelength interval are of interest. These integral quantities ought to be accompanied by a reliable uncertainty statement, for example, to assess conformity with prescribed limits or in order to judge the consistency of results obtained at different laboratories. We have developed a generally applicable Monte Carlo procedure for evaluating the uncertainty of spectral measurements. The procedure naturally accounts for correlations in the SPD which turn out to be crucial. Means are provided to handle and transfer these large-scale correlation matrices easily. The proposed approach is illustrated by the determination of the SPD of colored LEDs from array spectroradiometer measurements, together with the derived CIE 1931 color coordinates. MATLABTM software implementing the proposed analysis procedure is made available.

Precise spectral and colorimetric simulations in commercial ray-tracing software require realistic light source models, which provide spectral information as a function of angle and spatial dimension. We describe and validate a general workflow to create hyperspectral LED models as a linear combination of spectral models. The workflow only requires user-defined precisions and ray files obtained with different optical filters. The ray files are transformed into histogram-based models, whose precision is evaluated by normalized cross-correlation values of their intensity distributions in the near-, mid-and-far field. Additionally, the concept is evaluated with a spatial and spectral well-defined test device.

To simulate and optimize optical designs regarding perceived color and homogeneity in commercial ray tracing software, realistic light source models are needed. Spectral rayfiles provide angular and spatial varying spectral information. We propose a spectral reconstruction method with a minimum of time consuming goniophotometric near field measurements with optical filters for the purpose of creating spectral rayfiles. Our discussion focuses on the selection of the ideal optical filter combination for any arbitrary spectrum out of a given filter set by considering measurement uncert-ainties with Monte Carlo simulations. We minimize the simulation time by a preselection of all filter combinations, which bases on factorial design.

Luminous intensity distributions enable an evaluation of the spatial radiation characteristic of a light source. This radiation characteristic is determined by the structural properties of the light source, its operating parameters and the properties of the measuring system. This paper describes some possible methods and rules for comparing luminous intensity distributions. The focus is on the development of calculation rules for quantifying the differences between two luminous intensity distributions. The difference measures developed allow the user to establish an objective comparison between luminous intensity distributions, this comparison being completely independent of the measuring system, the properties of the luminous intensity distributions and the users themselves. Further, the dependence of the properties of luminous intensity distributions resulting from measurement practice, such as adjustment uncertainties, regions that cannot be covered or measured, deviations of the total luminous flux, data noise and resolution differences, are discussed, and appropriate pre-processing and correction steps proposed. In addition, various visualisations of the differences between two luminous intensity distributions are demonstrated and the functionality of the difference measures developed is documented.

In lighting calculations and simulations, the emission of a light source is conventionally modelled using the far-field intensity, also termed luminous intensity distribution (LID). Previous studies have indicated that the traditional limiting photometric distance, to reach far-field conditions, is not always easy to determine. The limiting photometric distance, also called the photometric limiting distance of a light source is the shortest distance between the reference plane of a light source and the effective reference plane of a photometer, for a given acceptable error considering the photometric inverse square laws (ISO/CIE 19476:2014, 2014). This distance is dependent on the size of the light source, the luminous intensity distribution (beam angle), the spatial luminance distribution and the predetermined acceptable measurement error. In this paper the problems are analysed in detail for a disk-shaped light source, a linear light strip and a worst case scenario using two small (point) sources separated by a certain distance. The limiting photometric distance is investigated using different measures of error - not only for the main illumination direction but also at different angles of emission.

Near-field goniometric measurements are employed to determine the photometric characteristics of lightsources, i.e. the spatial and angular distribution of the emitted light.To this end a complex measurement system consisting of a goniometer and a CCD-based imaging photometer is employed. In order to gain insight into the measurement system and to enable a characterization of the whole measurement setup we propose to apply a computermodel to conduct virtual experiments. Within the computer model the current state of all parts of the virtual experiment can be easily controlled. There liability of the computer model is demonstrated by a comparison to actual measurement results. As an example for the application of the virtual experiment we present ananalysis of the impact of axial malpositions of the goniometer and camera.

Thema der Arbeit ist die Entwicklung und Implementierung eines Verfahrens zum Vergleich von Lichtstärkeverteilungskörpern. Hauptbestandteil des Verfahrens zum Lvk-Vergleich ist die Entwicklung von Berechnungsvorschriften zur Quantifizierung der Unterschiede zweier Lichtstärkeverteilungskörper. Die entwickelten Differenzmaße ermöglichen einen objektiven, vom Anwender, von den Lvk-generierenden Messsystemen und von den Parametern der Lvks unabhängigen Vergleich. Aus der Messpraxis resultierende Eigenschaften von Lvks wie Justageunsicherheiten, nicht messbare Lvk-Bereiche, Abweichungen der Gesamtlichtströme, Datenrauschen und Auflösungsunterschiede werden algorithmisch berücksichtigt. Zusätzlich werden verschiedene Varianten zur Visualisierung der Unterschiede zweier Lichtstärkeverteilungskörper vorgeschlagen.

Messverfahren mit klassischen Goniophotometern behandeln die leuchtenden 3D-Oberflächen von Lichtquellen wie Punktlichtquellen d.h. sie geben die Wirkung der Lichtausstrahlung nur für große Abstände als Lichtstärkeverteilungskörper an /4/. Ein Nahfeldgoniophotometer ist ein Goniophotometer mit dem Messungen im Nahfeld der Lichtquelle ausgeführt werden und dessen Photometerkopf durch eine Leuchtdichtemesskamera ersetzt wurde /7/. Damit wird die Wirkung der Ausstrahlungscharakteristik für einzelne Elemente der realen oder einer virtuellen Oberfläche der Lichtquelle als Verteilung von Leuchtdichten erfasst und als Strahlenfeld gemessen.

In this paper, we present the near-field goniophotometer setup recently installed at PTB for the photometric characterization of solid-state light sources, e.g. LEDs, under near-field conditions. Moreover, as a validation of the near-field goniophotometric measurements, the luminous intensity distribution of two LEDs determined by near-field measurements is also presented and compared with those carried out separately under far-field conditions using a photometer.

Die Arbeit soll einen Überblick über die aktuell existierenden Messtechniken zur Ermittlung von Lichtstärkeverteilungen geben. Dabei liegt das Hauptaugenmerk darauf, zu zeigen, für welches Messobjekt welche Messtechnik anwendbar ist. Wo sich Schnittmengen finden, also mehrere Messtechniken für dasselbe Objekt abwendbar sind sowie umgekehrt, und wo zu separieren ist. Es sollen Gemeinsamkeiten und Unterschiede zwischen den Messtechniken und sich daraus für die Vermessung von konkreten Messobjekten ergebende Vor- und Nachteile behandelt werden.

Das Erstellen von physikalischen Strahlenmodellen ist äußerst aufwendig und kann die Realität immer nur endlich genau erfassen. Gemessene Strahlendaten beschreiben die Lichtquelle dagegen genau. Die ermittelten Werte verbessern die Simulation von Leuchtquellen, beschleunigen den Entwicklungsprozess und lassen sich in die Datenformate der gängigen Simulationswerkzeuge exportieren.

Für die Entwicklung und Bewertung von Leuchten ist die Messung der Lichtstärkeverteilungscharakteristik (LVK) wesentlich. Moderne Reflektorsysteme von Leuchten oder Scheinwerfern und die Simulation von LED Baugruppen erfordern oftmals die reale Ausstrahlungscharakteristik der Leuchtmittel, die entweder durch komplexe Simulationen oder durch Messungen ermittelt werden. Vielfache Anwendung finden gemessene Strahlendaten (4D Leuchtdichtedaten), die üblicherweise von den Lampen- bzw. LED – Herstellern zur Verfügung gestellt werden oder auf einem geeigneten Meßsystem gemessen werden können.

The ray data measured by means of modern near-field goniophotometers open up new ways in the development of optical systems. For numerous applications, synthetic models of radiation characteristics are insufficient for realistic optical simulations. The near-field goniophotometers type RiGO801 developed by the TechnoTeam company measures the real 4D- luminance distribution of measuring objects and provides ray data for various simulation programs.

Im Jahre 1991 wurde von Prof. Riemann die Idee entwickelt, mit bildauflösender Leuchtdichtemesstechnik Lichtstärkeverteilungen im Nahfeld zu messen. Gegenüber der Fernfeldmessung ergeben sich einige ganz wesentliche Vorteile. Für die Fernfeldmessung mit Drehspiegelgoniophotometern oder Goniometern mit langem Arm sind beträchtlich große Räume erforderlich. Die Nahfeldgoniophotometer RiGO erfordern einen Raum, der es gestattet eine Messkamera um das Messobjekt herum zuführen. Es sind also Raumgrößen L*B*H von etwa jeweils dem Zweifachen der Messobjektgrößen erforderlich. Ein weiterer wesentlicher Vorteil ist, dass das Messobjekt bei der Messung in Ruhelage verbleiben kann. Seit 1994 sind die Messsysteme im Einsatz. Bisher wurden mehr als 20 Systeme realisiert, für die Vermessung von LED bis zur Vermessung von großen Leuchten mit Abmessungen von 2000 mm oder auch für die Vermessung von Light-pipe.