Zbornik - SDR

“Colour rendering index of LED light sources” R-4
Table 1: Light source characteristics used in the present experiment
Description of
light source
Correlated
colour
temperature, K
Ra
CIE A 2856 100
CIE D65 6505 100
FL 3.5 4086 96
FL 3.12 2984 93
FlLamp 7226 87
CIE FL 7 6497 86
CIE FL 11 3999 83
p-LED (cool) 9310 80
p-LED (warm) 2976 77
CIE FL 2 4225 64
CIE FL 4 2938 51
RGB-LED1 2788 44
RGB-LED2 2788 27
RGB-LED3 2788 -17
In this new experimental paradigm the image of a scene was selected, where the spectral
reflectance was known for every pixel. In the present experiment we used an image kindly supplied
by Nascimento and co-workers 40 . Figure 8 shows the image rendered as it would look under D65
illumination. The test images were calculated from this hyperspectral image, using the SPDs of the
sources enumerated in Table 1.
Figure 8: Image used in the present experiment.
The white point of the generated test image is the white
point of the test illuminant it was calculated under. The main
concept of the simulation is that all images are shown in the
same chromatic adaptation environment (CRT display) to
eliminate factors such as colour memory effects that can
affect the result of the experiments negatively. The
CIECAM02 colour appearance model was used to transform
both images (illuminated by the test and the reference
illuminant) to D65, the white point of the monitor. This way
the differences between the colour appearances produced by
the test illuminants, independently of the CCT of the source
could be observed and judged.
7.1 Experiment
In the experiment to be discussed here three images were shown simultaneously on the screen at
one time in two rows. There were two images in the upper row and there was one in the middle of the
lower row. The lower image was fixed and showed the reference image. The observers’ task was to
“Lighting engineering 2006” stran 33