Lightness and Brightness and Other Confusions

Harald Arnkil
Lightness and Brightness
and Other Confusions
Introduction
Literature and speech concerning colour and light is full of confusing, conflicting
and contradictory usage. Take the very word colour. Sometimes it is
used to refer to the percept, the sensation of for example redness, at others to
the physical material, the paint, ink, dye or pigment acting as a stimulus for
the sensation of redness. It is quite natural for words to have different meanings
and usages in different environments, and the purpose of this article is
not so much to provide definitive meanings to them, but to draw attention to
the fact that different interpretations and meanings exist. The differences are
of no great concern in everyday speech, but in professional, educational or
research usage they can cause problems. Furthermore, there is hopefully
something to be learned about the very nature of human interaction with
light, colour and space from examining some of the different usages side by
side.
There are several types of confusions between terms and concepts dealing
with colour and light. One type of confusion arises from mixing concepts
belonging to different academic or professional traditions. An example of this
is confusing the photometrically defined measure luminance with the perceptually
defined attribute brightness.
Another type of confusion is exemplified by lightness and brightness. Both
terms have a specific and differentiated definition in perceptual science, but
at the same time they are a very familiar part of everyday language, where
their usages overlap without clear distinction as to their different meanings.
A third type of confusion often arises when general experiences or categories
have to be further defined for scientific purposes. These definitions can be
similar, but not exactly the same, in different conceptual systems. For example,
in everyday language we can talk about such as the vividness of a colour
and be rather certain that we can make ourselves understood; but in scientific
usage there are many terms and concepts, such as chroma, chromaticity and
chromaticness, having either the same or almost the same meaning.
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