The perceived atmosphere in a space is to a large extent determined by the illumination of the space, which usually is a
combination of artificial lighting and daylight naturally entering the room. In this study we investigated how the presence
of daylight affects the perceived atmosphere of a light ambience both in a real illuminated space and in a visualization of
the space. The perceptual accuracy of these visualizations has been demonstrated in previous studies for artificial
interior lighting, but not yet for the contribution of daylight to the interior lighting. Our results showed only a relatively
small effect of the contribution of daylight both on the perception of light and the perception of the atmosphere of an
interior light ambience. Possibly, adaptation plays an important role in this finding. Further, we demonstrated that the
perceptual accuracy of visualizations containing daylight was for the majority of the light and atmosphere perception
attributes similar to visualizations showing only artificial interior lighting.
It is well known that LEDs have problems with color consistency and color stability over time. Two perception
experiments were conducted in order to determine guidelines for the color and luminance deviations between LEDs that
are allowed. The first experiment determined the visibility threshold of hue, saturation, and luminance deviations of one
LED in an array of LEDs and the second experiment measured the visibility threshold of hue, saturation, and luminance
gratings for different spatial frequencies. The results of the first experiment show that people are most sensitive for color
deviations between LEDs when a white color is generated. The visibility threshold for white was 0.004 &Dgr;u'v' for a
deviation in the hue of the LED primaries, 0.007 &Dgr;u'v' for a deviation in the saturation of the LED primaries and 0.006 &Dgr;u'v' for a deviation in the luminance of the LED primaries. The second experiment showed that the visibility of hue
gratings is independent of spatial frequency in the range of 0.4 to 1.2 cycles/degree. However, for saturation and
luminance gratings there was a significant effect of spatial frequency on the visibility threshold. Both experiments show
that observers are more sensitive to hue than to saturation deviations.
This study investigated the effect of the chromaticity and intensity of the ambient illumination on the adapted white point of a homogeneous image (i.e. the chromaticity that is perceived as achromatic) and on the optimal white point of natural images (i.e. the white point with the most preferred color rendering). It was found that the adapted white point and the optimal white point shift towards the chromaticity of the ambient illumination. The effect of illuminant color was approximately 2.5 times larger for the adapted white point than for the optimal white point. The intensity of the ambient illumination had no effect on the adapted white point and the optimal white point, except for images with face content. In agreement with previous studies, the optimal white point was found to strongly depend on image content. The results indicate that the optimal color rendering of natural images is a complex relation of image content and ambient illumination.