Evaluation of daylight simulators. Part 2; Assessment of the quality of daylight simulators using actual metameric pairs†

Abstract

This paper discusses two methods for evaluating the quality of daylight simulators, namely the band‐value method specified in British standard BS 950 and the CIE metamerism index method. Six daylight simulators of various types and manufacturers were used for the assessment and a psychophysical experiment was conducted to evaluate the two methods. A range of 70 metameric pairs was assessed by a panel of observers under each of the six simulators and the reliability of their visual results was examined in terms of observer accuracy and repeatability. The visual results were also compared for each pair of simulators to reveal how the results could be affected by using different simulators. The effectiveness of four colour difference formulae was tested using the visual results. Finally, four methods were developed using two statistical measures of performance factor, band‐value deviation and CIE metamerism index for evaluating the quality of daylight simulators.

Metamerism and shade sorting

“…The CIE special metamerism index, which is the average colour difference of the metamers, was defi ned for both visible and ultraviolet ranges (denoted as MI vis and MI uv , respectively). The daylight simulator is rated from A to E, based on metamerism index value of < 0.25, 0.25-0.5, 0.5-1.0, 1.0-2.0, > 2.0 CIELAB colour difference units, respectively (Xu et al , 2003).…”