Ingineria Iluminatului - Journal of Lighting Engineering - Prof. Florin ...

PREDICTION OF COLOUR APPEARANCES
IN NAYATANI, HUNT, CIECAM AND NC-IIIC SPACES FOR COMPARISON WITH
PERCEIVED ATTRIBUTES OF MUNSELL COLOURS
1. Introduction
12
Koichi IKEDA, Shinichiro NODA
Department of Electrical Engineering,
Faculty of Science & Technology TOKYO RIKA DAIGAKU
High Intensity Discharge (HID) lamps have been commonly used in the field of stadium and open
space. However, recently, HID lamps come into general use for indoor lighting. Accordingly,
specification of colour rendering properties of HID lamps becomes necessary for practical lighting
design. In this study, in order to investigate perceived colour appearances under various High
Intensity Discharge (HID) lamps, perceived appearances of 40 Munsell colours with value of 6 and
chroma of 8 have been subjectively evaluated under Xenon lamp (Standard illuminant D65),
incandescent lamp (Standard illuminant A), metal halide lamp MT400DL, fluorescent mercury lamp
HF400X and high pressure sodium lamp NH360. These psychological attributes have been
compared with predicted metric quantities in Nayatani, Hunt, CIECAM and NC-IIIC spaces. Then, it
is found that metric quantities of test colours in the new uniform colour space NC-IIIC correspond
more properly with perceived attributes under the illuminations of HID lamps than those in
traditional colour spaces. Therefore, in the specification of colour rendering properties of light
sources, the NC-IIIC space is superior to other colour spaces.
It is generally known that colour appearances vary
according to the change of the illuminant in spite of the
chromatic adaptation of the visual system. These
characteristics of illuminant on colour perception are
called colour rendering properties of light source.
For the specification of colour rendering properties
of light source, the uniform colour space U*V*W* was
recommended by the CIE in 1974 to calculate
colorimetric quantities of test colours under test and
reference illuminants.
This colour space, however, has been used only for the
calculation of colour rendering indices and not for other
colorimetric purposes. Also this space is inadequate to
specify coordinates of colours because of enormous spatial
distortions in the regions of red and green colours.
Then a new method for the assessment of colour
INGINERIA ILUMINATULUI 15-2005
rendering using CIE chromatic adaptation formulae
and the uniform colour space L*a*b* was proposed by
the Technical Committee 1-33 of the CIE in 1996. In
L*a*b* space, however, chroma is estimated larger in
the yellow region, and conversely smaller in the blue
region. For the reason of these spatial distortions in the
U*V*W* space and the L*a*b* space, three
components of colour shift, i.e., differences of hue,
lightness and chroma, cannot be represented
orthogonally and independently.
Further more, Nayatani model, Hunt model,
CIECAM model and NCIIIC space have been
developed for the prediction of colour appearances
under various illuminants.
Practical evaluations of these models, however,
have not been sufficiently completed enough, because
quantitative data for comparison between predicted
appearances in these spaces and subjectively estimated
perceived appearances are not plentiful enough.