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NORDIC LIGHT & COLOUR
41
tion). If focusing on colour in spatial context, colour and light
theory is given theoretical connection to our intuitive under-
standing of the world around and can be part of a wider field of
aesthetic research and education.
Colour, light and physics
In the field of colour and light, visual/perceptual phenomena
too often are described and analysed with the use of physically
based concepts. This can give the impression that physical
measurements also measure what we see. But this impres-
sion is false and it is not only a question of simplification. Using
physically based concepts to describe perception of colour
and light may be both misleading and incorrect. This does not,
however, mean that concepts referring to abstract but mea-
surable structures of the physical world are not useful. But
they are useful only as long as they are used to describe the
material world. It is, for example, necessary for paint industries
and light source industries to have instruments to control and
maintain physical standards of their products.
We experience colours intuitively as properties belonging to
the outer world. In the physical world – beyond the reach of the
senses – the existence of colour and light can only be dem-
onstrated indirectly by measuring spectral electromagnetic
radiation with wavelengths between approximately 380 nm and
760 nm. The human eye responds to this radiation, but the rays
themselves are not visible. Isaac Newton remarks that “the
rays, to speak properly, are not coloured”. In them there is
nothing else than a certain power and disposition to stir up a
sensation of this or that colour” (Newton 1704).
It is true that experience of colour and light is dependent on
electromagnetic radiation but the colour of an object are only to
a certain degree dependent on spectral distribution of the ra-
diation that it reflects. The Norwegian neurophysiologist Arne
Valberg states: “The reflection properties of surfaces relative
to their surround are more important for colour vision than
the actual spectral distribution reaching the eyes.” (Valberg
2005: 266). The American philosopher C.L. Hardin concludes
that there is no “reason to think that there is a set of external
physical properties that is the analogue of the (colours) that we
experience” (Hardin 1993: xii).
Colour, light and adaptation
The relationship between the physically measurable and vi-
sion is complicated. Our perceptual systems counterbalance
physical changes in the world around. Our vision is based on a
continuous adaptation, which strives to keep the colours of the
surrounding world.
When perceiving colours, our vision does not register the abso-
lute intensity or the absolute spectral distribution of radiation
that reaches our retina. Instead
distinctions
and
relations
are
registered. Hence our visual system is developed for a continu-
ous spectrum of light and gradual changes between different
illuminations. Under these circumstances we perceive colours
as more or less constant if our visual system has had time to
adapt to the specific light situation.
The mechanisms that make us perceive and determine the
lightness of surfaces observed in different situations have been
thoroughly considered by Alan Gilchrist et.al (1999). Gilchrist
et al. state that it is not the luminance that determines the
perceived lightness of a surface. Any luminance level can be
perceived light or dark depending on context, and the surface
that we perceive as white functions as an “anchor” for per-
ceived lightness of all other surfaces seen simultaneously.
Most often our anchor for ”white” is defined as the surface that
has the highest luminance in the visual field –
Highest Lumi-
nance Rule.
This is, however, not true in all situations, since we
also have a tendency to perceive the largest area in the field of
vision as anchor for ”white” –
Area rule
. As long as the lightest
area also is the largest, the two rules coincide, but they come
into conflict if the darker one also is the largest. Then we tend
to perceive the largest area as white at the same time as the
smaller and lighter area also is perceived as white - a paradox
that is solved by perceiving the smaller area as luminous.
But even if we experience that an object has the same colour
in different light we can at the same time perceive a slight tone
of colour that reveals the character of
light
. All colours have
at least a slight chromaticness and a hue. We never experi-
ence absolutely neutral – achromatic – colours (Fridell Anter &
Klarén 2009). For nominally white surfaces this effect is more
obvious than for nominally chromatic surfaces. We experience
the surface as white but we understand at the same time that it
is illuminated with a light of a special quality and intensity. This
involves not only light coming directly from the light source,
but also reflected light from surrounding surfaces. Reflection
from chromatic surfaces in a room can give a hue to a nomi-
nally neutral or slightly chromatic surface, which is especially
evident in nominally neutral light surfaces (Billger 1999).
Klarén & Fridell Anter (2011) have shown that the “lightness
anchor” also functions as a perceptual anchor for experience
of hue. With an analogy from music theory white anchoring
could be regarded as a ”transposition” where the surface that
is perceived as white is the ”keynote” – or ”keycolour” – for
perception of both lightness and hue in a given light situation;
the ”keycolour” decides all relations between the colours in the
field of vision.
The French philosopher Merleau-Ponty (2002: 355) discusses
how we experience the surrounding world in different ways
depending on situation. He makes a distinction between two
modes of attention: he talks about
the reflective attitude
and