CIE 135-1999

This volume contains short Technical Reports and Research Notes prepared by various Technical Committees and Reporters within CIE Division 1 and 2.

135/1 Disability glare>

On the basis of a preceding theoretical analysis of experimental data on disability glare published in CIE Collection (Vos and Van den Berg, 1997), resulting in a complete glare equation covering the full 0° to 100° glare angle range, three simplified glare equations are presented, each of them defined for a more restricted glare angle domain. This ensemble of three equations together is recommended to define a CIE Standard Glare Observer; the most simple one, the Age Adapted Stiles-Holladay Equation, will suffice for most circumstances of daily practice.

This report was prepared by J.J. Vos, The Netherlands (TC 1-18 Chairman)

135/2 Colour rendering, closing remarks

The CIE "Test method to calculate a colour rendering index" has a long and complicated history. After first publishing a method in 1965 and updating it in 1974, it was soon realised that further amendments would be necessary. A TC worked on the subject in the 1980s, but had to be closed without any definite recommendation due to disagreements among the TC Members. A second trial was started after the 1991 Quadrennial Meeting. This TC worked - under various chairmen - for about six years, but again it had to be closed without producing a definite recommendation, although this time TC Members agreed in a number of questions. This report summarizes those items where TC Members could agree and highlights also those questions where no consensus could be reached. To the latter category two groups of questions belong: items where it is hoped that CIE will come up very soon with further recommendations that should be incorporated in a colour rendering calculation (e.g. new chromatic adaptation transformation) and items where a political decision of the lamp manufacturers is needed, as a change in the calculation method necessarily will favour one lamp spectrum compared to that of an other. The present closing remarks document summarizes the items discussed by the TC during the past decade, states those items where a consensus could be formed and pinpoints questions where further research is needed to reach consensus.

This research note was prepared by J. Schanda, Hungary (TC 1-33 Chairman)

135/3 Virtual metamers for assessing the quality of simulators of CIE illuminant D50 (Supplement 1-1999 to CIE 51-1981)

CIE 51-1981 describes a method of assessing the quality of simulators of CIE illuminants D55, D65, and D75 (various phases of daylight), for colour measuring instruments, visual appraisal and matching of colours. The spectral power distribution of the simulator is measured and the departure from the ideal distribution is computed, in terms of chromaticity differences between virtual metameric pairs that match under the ideal CIE illuminant. CIE illuminant D50 is simulated for use in photography and colour printing. This supplement provides the virtual metamers needed to apply the method of assessment to D50 simulators.

135/4 Some recent developments in colour-difference evaluation

A compressed overview is given of developments in colour-difference evaluation that trace back to the early beginnings by MacAdam. The correlation of colorimetric measures of coloured samples with judgements on small colour differences follows normal statistics, but in a three-dimensional space. A wide diversity of experimental conditions in investigations of the colour-difference effect made comparisons of different studies troublesome. Some external influential factors could be identified. Recently developed data sets resulted from much better control of experimental conditions. They form a new basis for deriving colour difference formulae. The CIE is the international body to encourage field research for optimising new colour-difference formulae. The various stages for recommending formulae and exchanging extensive investigation documents make a close link between practitioners and theorists, however, in general industrialists have a faster response. Nonetheless, the CIE still remains the mother-body for international discussion and agreement. Recent developments in colour-difference evaluation show an acceleration of the work of CIE TCs. Their studies first improved the CIELAB-formula, and second now try to fill the gap between the CIE94 and the older CMC(l:c) solutions. A new idea is introduced to optimise the formalism of a formula not at the components of differential terms, but at the co-ordinates which keeps the vector definition of colour-difference as in the CIELAB-formula. An international discussion is proposed on this aspect as a forthcoming step to further improvement of colour-difference evaluation.

This report was prepared by K. Witt, Germany

135/5 Visual adaptation to complex luminance distribution

One of the most important and difficult tasks in evaluation of perceived brightness in everyday circumstances is to assess what level the visual system adapts to. Especially, this is an inevitable process when putting the new photometric system into practice. In the present report, several studies are reviewed, and tasks and problems of the prospective TC are discussed. Although many studies of brightness perception are potentially related to the matter of adaptation level, we can find no literature in which the issue is discussed explicitly. All what we can do now is to encourage investigators to carry out research concerning the level of visual adaptation not only in experimental conditions but also in natural and complex environments.

This research note was prepared by H. Shinoda, Japan

135/6 45°/0° Spectral reflectance factors of pressed polytetrafluoroethylene (PTFE) powder (Reprint of NIST Technical Note 1413)

Pressed polytetrafluoroethylene (PTFE) powder is used for 45°/0° reflectance factor standards. The radiometric and spectrophotometric measurement community such as the Council for Optical Radiation Measurements (CORM) has demonstrated the need for such a standard and its application to quality control and quality assessment. This publication briefly describes the instrumentation used for the 45°/0° spectral reflectance factor measurements of pressed PTFE powder from 380 nm to 770 nm. Also, the variations of 45°/0° reflectance factor with sample preparation and materials are discussed. The expanded uncertainty at a coverage factor of two for the 45°/0° reflectance factors of pressed PTFE powder ranges from 0,009 to 0,017.

This report was prepared by P.Y. Barnes, USA and J.J. Hsia, USA (Reprint of NIST Technical Note 1413 July 1995)

The publication contains also abridged abstracts of CIE Publications prepared within Division 1 and 2.

These reports are written in English, with short summaries in French and German. The publication contains 78 pages.