Lightness and Brightness and Other Confusions
Lightness and Brightness and Other Confusions
Lightness and Brightness and Other Confusions
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Adelson is talking here about light coming from images <strong>and</strong> scenes, because<br />
his article discusses mainly two-dimensional lightness illusions. But let us not<br />
be confused by that; his definitions apply just as well to spatial contexts.<br />
The term brightness refers to the human experience of the intensity of light<br />
reflected or emitted by objects <strong>and</strong> surfaces. The sky, the moon or a c<strong>and</strong>le<br />
flame has brightness, rather than lightness. But – as Adelson points out –<br />
also surfaces have brightness in addition to lightness, <strong>and</strong> their brightness<br />
depends on how much light they are perceived to reflect at a given moment.<br />
In a spatial or natural context, then, lightness refers to an object’s particular<br />
perceived surface quality, to the surface’s or object’s overall ability to absorb<br />
<strong>and</strong> reflect light. <strong>Brightness</strong> refers to the experience of the amount of reflected<br />
or radiated light in relation to the overall, or global, scene.<br />
Whiteness<br />
A distinction must be made also between lightness <strong>and</strong> whiteness. Whiteness<br />
<strong>and</strong> blackness are parameters of colour in the NCS system <strong>and</strong> they are sometimes<br />
confused with the concepts of lightness <strong>and</strong> darkness. Unlike lightness<br />
<strong>and</strong> darkness, whiteness <strong>and</strong> blackness are discreet concepts, rather than<br />
expressions of the presence <strong>and</strong> lack of something. They are defined as relative<br />
visual similarity to the elementary colours black <strong>and</strong> white. The geometric<br />
model of the NCS colour space also includes the variables hue <strong>and</strong> chromaticness.<br />
Unlike all other systems (save the now obsolete Ostwald system)<br />
the NCS does not directly include lightness or brightness as one of its variables.<br />
Whiteness <strong>and</strong> blackness do contribute to the lightness <strong>and</strong> darkness<br />
(as well as to the chromaticness) of colours in the NCS system, but they have<br />
an indirect relation to lightness: in order to derive lightness from NCS whiteness<br />
<strong>and</strong> NCS blackness also hue must be taken into account: a yellow with<br />
five percent of whiteness is far lighter than a blue with the same percentage of<br />
whiteness. The reason is that yellow <strong>and</strong> blue are of different lightness to start<br />
with. The same goes for blackness in relation to the different hues. So what<br />
are whiteness <strong>and</strong> blackness, if not lightness <strong>and</strong> darkness? They are the<br />
visual constituents of a colour’s impurity, its lack of vividness or distance<br />
from the ideal pure chromatic hue. As perceived phenomena they could be<br />
described as either mistiness or milkiness or fogginess in the case of whiteness,<br />
<strong>and</strong> shadiness in blackness or greyishness when both whiteness <strong>and</strong><br />
blackness are present.<br />
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