Lightness and Brightness and Other Confusions

of the sky). This is denoted by visual concepts such as surface colour, volume
colour and film colour. (Katz 1935).
A surface colour is perceived as being part of the surface only. One example is
an opaque paint surface. A volume colour is perceived as permeating the
whole volume of an object or substance. Examples of this are coloured glass,
gas, mist and water. A luminous colour is perceived as belonging to a shining
object, such as a light source. Here it is important to remember that these
concepts are visual and phenomenological, they describe what we see and not
the underlying physical cause. For example, in pictorial art, the painter can
create the experience of light by skilful use of contrast – and those spots on
the canvas are, as perceived, luminous colours. 53 (Fig. 9)
Figure 9. This colour combination is an expressive symbol for the contrast
situation perceived in shining and self-luminous objects, such as a lamp in
darkness or light through an opening. (See Natural Experience, pp. 26, 30).
The middle part of the figure is a luminous colour in Katz's sense.
(Illustration: Ulf Klarén)
The visual properties of a colour can be described with words such as hue,
value, nuance, etc. Several of these terms are ambiguous and thus not scientifically
usable unless they are further defined. 54 NCS (Natural Colour System)
is a coherent system for colour description, based purely on visual assessment.
It categorises the perceived colour in comparison to perceptual
standards that are understood as inherent to the human visual system. The
elementary colours yellow, red, blue, green, white and black are defined as
having no similarity to any other colour than themselves. Hue is, according to
the NCS, the specific colour’s relative similarity to the chromatic elementary
Gilchrist et al. 2007 ; Fluorent or luminous colours are discussed in da Pos 2005. For
a further discussion about visual categories such as transparency, depth, translucence,
etc. see Fridell Anter 2006, p 142.
The confused use of some of there terms is discussed in the article Lightness and
brightness in this volume.
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