electronic displays Conference 2016

Measurements with conoscopic lenses together with ILMDs (Imaging Luminance/Color Measuring Devices) can support the characterisation of displays and materials during the R&D and production process. Using a conoscopic lens the angular dependence of luminance/color can be measured with only a single measurement. Using different geometrical relations between the device under test, the conoscopic lens and different illumination conditions a lot of display and material properties can be measured with one or a few measurements only. The article shows the working principle of conoscopic lenses in detail. Furthermore the measurement of the angular dependent luminance/color, the angular dependent contrast and the measurement of selected angular dependent material properties (e.g. transmission and reflection characteristics of glasses) are presented. For all applications the advantages and limitations of the conoscopic lens measurements are explained to suggest the right fields of application for this measurement method.
Authors: U. Krüger; F. Schmidt

SID Vehicle Displays & Interfaces 2019

Modern automotive displays may be sensitive to static content, which remains as an undesired effect of either temporary vanishing or being a static ghost image within the refreshed content. Therefore, there is a development of measurement procedures to quantize the degree of image sticking [1- 6]. Different aspects of these methods as the grey level dependencies or the importance of a temp-oral alignment were considered in [7]. But the mathematically necessary separation of unavoidable initial non-uniformities and the actual image sticking was excluded in that research.
This contribution concentrates on the performance of two selected image sticking evaluation methods [5, 6] from the automotive community and [1] for reference. After briefly introducing the three methods, this contribution focusses on their capability of separating initial non-uniformities from the actual sticking image effect of the target display. Therefore, a mathematical analysis, which is based on a simple but physically motivated sticking image model, is performed. Based on that, an additional non-uniformity correction is proposed. This additional correction has a positive influence on the precision but a negative influence on the measurement time of the fastest measurement method [6]. Thus, we propose a workflow, that decides based on the properties of the DUT whether the correction is necessary or not. All conclusions are supported by simulations and validated using measurement results of a randomly chosen non-uniform automotive LC display.
The aim of this paper is on the one hand to quantize the mathematical influence of the methods and on the other hands to suggest a workflow, which utilizes an existing method and optimizes its application with respect to precision and overall measurement time.
Authors: I. Rotscholl; U. Krüger

SID Vehicle Displays & Interfaces 2018

There are several optical display attributes, which require optical and photometric measurements during R&D activities or quality control and conformity assessment for automotive applications. The aim of this research paper is to assess typical properties of luminance based display measurements with respect to different optical display attributes. The measurement properties include on the one hand characteristics of the measurement equipment and on the other, the characteristics of the measurement method.
Based on the general working principle of ILMDs (imaging luminance measurement device), we briefly explain typical ILMD characteristics as well as the concepts of repeatability, reproducibility, precision and measurement uncertainty [1]. Afterwards, optical display properties as well as measurement methods [2, 3, 4] are introduced.
Finally, we qualitatively and quantitatively assess chosen influences of ILMD specifications and different measurement procedures on the obtained results.
Thus, this work shall convey a feeling for photometric display metrology requirements under the consideration of the measurement task and the desired precision
Authors: I. Rotscholl, U. Krüger

Advanced Optical Technologies

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.
Authors: I. Rotscholl; K. Trampert; F. Schmidt

Information Display

More and more, the suppliers of near-to-eye displays (NED) are seeking cost-effective imaging luminance and color measurement solutions that are adaptable to their instrument structures. Here, the authors offer a set of formulas that determine the basic parameters of imaging luminance and radiance measurement devices and lenses for different NED-concepts.
Authors: N. Schuster; U. Krüger; T. Porsch

Przeglad Elektrotechniczny

Glare is one of the most important parameter of lighting quality. Despite the passage of time from the beginning of glare research, no standard of conducting laboratory experiments was proposed. In the article the review of solutions related to glare assessment is presented. The method of conducting research on glare is also described. The authors pay attention to the most important aspects in the methodology of glare assessment for the experimental research on glare and glare assessment based on UGR measurements. The tests of the new algorithm for UGR calculation is presented — algorithm for precise identification and extraction of glare source area from HDR image.
Authors: D. Sawicki; A. Wolska; T. Porsch

Society for Information Display

Imaging Luminance and Color Measuring Devices (ILMD, ICMD) also called Array Detectors in combination with adapted measuring lenses provide effective one-shot solutions to evaluate modern Near-Eye Displays (NED). Basic parameters of those lenses depend on the NED-arrangements under test.

Corresponding equations are deducted. The application of two new measuring lenses shows a way to generate a series of measuring lenses.
Authors: N. Schuster; U. Krüger; T. Porsch

Proceedings of the International Display Workshops Volume 26 (IDW '19)

The “Uniformity measurement standard for Displays”, which is used for automotive applications, describes precise setup and alignment procedures to ensure reproducible measurement results. However, the influences of the tested device and the ILMD are not considered in detail. This contribution shows experiments and simulations to estimate these influences as well.
Authors: I. Rotscholl; T. Porsch; U. Krüger

Society for Information Display

Image Sticking is an undesired display property, which requires time-consuming and expensive testing. This study summarizes some proposed Image Sticking evaluation methods and identifies relevant differences. It derives aspects, which should be considered prior to a time-consuming and potentially irreversible Sticking Image measurement. Further, parameter analysis associated with the Imaging Luminance Measurement Device is briefly outlined.
Authors: I. Rotscholl; U. Krüger

International Conference on Display Technology (ICDT 2019)

This contribution aims to describe the challenges associated with the characterization of NED (Near-Eye Displays) using Imaging Luminance and Color Measuring Devices. Based on the special attributes of NED systems, the requirements for the measurement set-up are deduced. Then two special lens designs, the hypercentric lens and the front stop lens, which both overcome these challenges, are introduced. This includes their concepts, applications and presentation of exemplarily obtained results.
Authors: B. Liu; T. Porsch; N. Schuster; I. Rotscholl; U. Krüger

Society for Information Display

To decide whether a display works according to the specification it is not only necessary to take the measurement values into account. The measurement uncertainty also plays a significant role in this decision. Besides some basic knowledge about the measurement uncertainty evaluation, the paper shows the main contributions and their influences for the key values of the BlackMURA standard. Using the rules of conformity assessment, the use of tolerance intervals and acceptance intervals is explained in detail to give all parties (OEMs, manufacturer of display and measurement system manufacturer) the chance to discuss their quality metrics in a reasonable manner.
Authors: I. Rotscholl; U. Krüger; B. Liu


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.
Authors: I. Rotscholl; K. Trampert; U. Krüger; I. Leopoldo Sayanca; F. Schmidt; C. Neumann

LED Professional

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.
Authors: I. Rotscholl; K. Trampert; U. Krüger; I. Leopoldo Sayanca; F. Schmidt; C. Neumann

Ilmenau Scientific Colloquium

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.
Authors: K. Bredemeier

KIT | 212

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.
Authors: I. Rotscholl


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.
Authors: K. Bredemeier; U. Krüger; F. Schmidt

Color Research & Application

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.
Authors: F. Schmähling; G. Wübbeler; U. Krüger; B. Ruggaber; F. Schmidt; R. Taubert; A. Sperling; C. Elster

SID International Symposium 2016

The requirements of automotive displays differ to a large extent from consumer and industrial displays. In order to reduce the effort in specifying and evaluating high quality displays, German automotive OEMs, Tier 1/2 and the German Flat Panel Forum have launched a cooperation.
Authors: K. Blankenbach; U. Krüger; H. Lauer, M. Zobl

SID International Symposium 2016

A method is proposed that characterizes the loss of image clarity caused by anti-glare coatings. The method uses high resolution imaging, giving a distribution of scattered light that can be related easily to the clarity impression of the human eye. Results of different AG treated cover glasses are shown and a new parameter is proposed to characterize the loss of image clarity. This can be applied to the specification and characterization of the cover glasses as well as the characterisation of the final product for quality assurance.
Authors: T. Fink; U. Krüger


Goniophotometry allows the measurement of high contrast distributions like headlamp low beam, rear lamps or other high dynamic distributions and has a very slow mismatch factor. But the measurement is slow and takes minutes up to hours for a complete distribution. Digital image processing is fast and provides a distribution in high resolution in few seconds. The solution for the customer is a combination of the speed and possibilities of digital image processing with the contrast and accuracy of a goniophotometer.
Authors: C. Schwanengel; F. Schmidt; T. Reiners; C. Diem

SID International Symposium 2016

We introduce the scattering-induced spreading of a narrow linear light source in transmission as an alternative method for characterization of image blurring induced by anti-glare layers. This novel method is compared to the recently presented concept of pixel crosstalk and to the transmissive scatter distribution function of anti-glare layers measured in two different ways. The reduction of transmittance modulation is presented as an additional method for characterization of image blur. The ranking of the results is compared to a generalized haze level of the AG samples as obtained from the transmittance distribution functions measured with two different methods.
Authors: M. Becker; T. Fink; U. Krüger

OSA Publishing | A1597-A1611

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.
Authors: I. Rotscholl; M. Katona; K. Trampert; U. Krüger; F. Schmidt; C. Neumann

DfwG Jahrestagung 2015

Die vorliegende Arbeit beschäftigt sich mit Einflussgrößen welche beim Einsatz einer Hyperspektral-kamera berücksichtigt werden müssen. Diese Einflussgrößen können direkt aus den Eigenschaften der verwendeten Filtertechnologie abgeleitet werden. Die betrachtete Hyperspektralkamera besteht aus einem elektrisch durchstimmbaren Filter (Liquid Crystal Tunable Filter LCTF) zur spektralen Zerlegung des Lichts, einem abbildenden optischen System und einem Matrixdetektor. Aufgrund dieses Aufbaus kann, bei entsprechender Kalibrierung, das Spektrum einer Lichtquelle ortsaufgelöst ermittelt werden. Die ortsaufgelöste Messung des Spektrums einer Lichtquelle erfolgt bei der vorliegenden Hyperspektralkamera nach dem Monochromatorprinzip, das heißt das Spektrum der Lichtquelle wird sequenziell abgetastet, man spricht hierbei von der Zerlegung des Spektrums in sogenannte Kanäle. Die Kanäle der Hyperspektralkamera besitzen Bandpasscharakter und sind quasi kontinuierlich (große Kanalanzahl) über den spektralen Arbeitsbereich des Systems verteilt. Die Bestimmung von farbmetrischen Größen erfolgt über das Spektralverfahren. Wesentliche Einflussgrößen beim Betrieb einer Hyperspektralkamera sind die endliche Bandbreite der Kanäle, der eingeschränkte Arbeitsbereich (400 nm – 720 nm) und das winkel- und temperaturabhängige Transmissionsverhalten der verwendeten Filtertechnologie. Der Einfluss sowie mögliche Korrekturen dieser Einflussgrößen werden in der vorliegenden Arbeit, anhand der Bestimmung von farbmetrischen Kennwerten von LEDs, untersucht.
Authors: B. Ruggaber; U. Krüger; F. Schmidt

Optics Express

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.
Authors: I. Rotscholl; K. Trampert; U. Krüger; C. Neumann

Lighting Research and Technology, November 4, 2015 | 62-83

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.
Authors: F. Gassmann; U. Krüger; T. Bergen; F. Schmidt

Tagungsbeitrag Lux junior 2015

Die vorliegende Arbeit beschäftigt sich mit Einflussgrößen welche beim Einsatz einer Hyperspektral-kamera berücksichtigt werden müssen. Diese Einflussgrößen können direkt von den Eigenschaften der verwendeten Filtertechnologie abgeleitet werden. Alle Betrachtungen beziehen sich auf die Zielsetzung, farbmetrische Kennwerte von LEDs, unter Verwendung einer Hyperspektralkamera, zu bestimmen.
Authors: B. Ruggaber; U. Krüger; F. Schmidt

LICHT 7/8 2015, p. 70-74

Die visuelle Erfassung von Information durch das menschliche Auge kann durch helle Lichtquellen gestört werden. Diese Effekte werden unter dem Sammelbegriff der Blendung zusammengefasst. In diesem Beitrag wird diskutiert, ob zum einen die Simulation und Vorhersage eines belastbaren Blendungsurteils und zum anderen die messtechnische Überprüfung einer realen Beleuchtungssituation anhand der vorhandenen Messdaten, Messmittel und Messmethoden überhaupt möglich sind. Dabei wird auf aktuelle Arbeiten zur messtechnischen Bewertung von subjektiven Blendungsurteilen in Innenräumen Bezug genommen.
Authors: T. Porsch, C. Funke; C. Schierz; F. Schmidt

Proceedings of the 28th Session of the CIE, Manchester; Vol. 1

Imaging luminance measuring devices (ILMD) are widely used in different fields of application. The assessment of glare caused by sun light and technical lighting installations for outdoor and indoor applications has meanwhile become reality. Measuring the discomfort glare for artificial indoor lighting installation is a fixed requirement of current standards. The aim of this study is to develop a simple and very well suitable software algorithm to fulfil those requirements by using the ILMD measuring technique comfortably. This paper also includes a comparison of currently existing equations for the discomfort glare regarding their technical requirements to be met by the ILMD and also the validation of new ideas and methods for analysis and evaluation. Keywords: Unified Glare Rating (UGR), Imaging Luminance Measuring Device (ILMD), discomfort glare
Authors: T. Porsch, C. Funke; C. Schierz; F. Schmidt

Proceedings of the 28th Session of the CIE, Manchester; Vol. 1

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.
Authors: V. A. Jacobs; P. Blattner; Y. Ohno; U. Krüger; P. Hanselaer; P. Rombauts; F. Schmidt

International Journal of Thermophysics 36(8) · June 2015

A CCD camera, which has been specially equipped with narrow-band interference filters in the visible spectral range for temperature measurements above 1200 K, was characterized with respect to its temperature response traceable to ITS-90 and with respect to absolute spectral radiance responsivity. The calibration traceable to ITS-90 was performed at a high-temperature blackbody source using a radiation thermometer as a transfer standard. Use of Planck’s law and the absolute spectral radiance responsivity of the camera system allows the determination of the thermodynamic temperature. For the determination of the absolute spectral radiance responsivity, a monochromator-based setup with a supercontinuum white-light laser source was developed. The CCD-camera system was characterized with respect to the dark-signal-non-uniformity, the photo-response-non-uniformity, the non-linearity, and the size-of-source effect. The influence of these parameters on the calibration and measurement was evaluated and is considered for the uncertainty budget. The results of the two different calibration schemes for the investigated temperature range from 1200 K to 1800 K are in good agreement considering the expanded uncertainty (k=2). The uncertainty for the absolute spectral responsivity of the camera is 0.56 % (k=2).
Authors: L. Bünger; K. Anhalt; R. D. Taubert; F. Schmidt

Eletricidade Moderna, Brasilien, März 2015, S. 114–121

A medição do incremento limiar, ou seja, da perda de visibilidade causda pelo ofuscamento, será uma exigência das normas futuras. Atualmente, o ofuscamento causado por instalaçoes de iluminação artificial ou plea luz natural já tem sido avaliado tanto em aplicaçoes internas quanto externas. Exte artigo descreve uma ferramente de software que utiliza dispositivos de medição de luminância por meio de iamgens para medir o incremento limiar.
Authors: T. Porsch; A. Walkling; A. Überschär; C. Schierz; F. Schmidt