Lightness and Brightness and Other Confusions

ecause the lower reflectance of p is counterbalanced by its higher illuminance.
Faces p and q appear to be painted with the same grey, and thus they have
the same lightness. However, it is clear that p has more luminance than q in
the image, and so the patches differ in brightness. Patches p and r differ in
both lightness and brightness, despite having the same luminances.
(Adelson 2000)
Why is it important to make a distinction between lightness from brightness?
The answer is that light and its effects on the visual quality of the environment,
in urban and road planning, work environments, etc., are now described
in the physically quantitative terms of radiant flux, illuminance and
luminance, and lightness and brightness are none of these. Neither are they
the same thing – and of the two, brightness is often confused with luminance.
It would be very useful to develop methods and tools for assessing and separating
these basic qualities of human visual experience. 73
Attempts to systemize colour
The International Commission on Illumination (CIE) has ever since its foundation
in 1913 played a central role in defining colour from physical and
psychophysical premises. The advent of computerized colour management in
the printed and electronic media has further reinforced the physical/psychophysical
view of colour and light. Both colorimetry and computer
colour management treat the mixing, augmenting and precise definition of
colour as a matter of measuring amounts of light energy in so-called RGBchannels
or as so-called tristimulus values. This of course makes huge sense
for controlling colour on computer and TV-screens, where the colours really
are produced with three types of phosphors. Problems start arising when the
software tries to simulate such psychological percepts as relationships of hue,
lightness, brightness and vividness. The first and biggest problem is that
(contrary to common belief) there are no RGB-channels in the human brain
on which to base the colour mechanisms of computers and colour measuring
instruments.
The difficulties of mapping human colour vision into a Cartesian space have
become more and more evident as neuroscience and psychology have revealed
new facts about the non-linear aspects of the visual processes. As
much as creators of colour systems would like it to be so, the variables of
Professor Anders Liljefors has suggested a method and a terminology for visual
analysis of light in spaces. (Liljefors 2005). A further development of the method is
under way and has been tested within the SYN-TES project in 2010–11. See Arnkil et al.
2011 and Matusiak et al. 2011.
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