Perceiving coloured objects and lights

It’s often assumed that we perceive the colour of an object based solely on the response of our eyes/cone cells to light from the object itself. In fact, the colour we perceive an object as having also depends very much on its context.

In the images above, we perceive similarly bright and colourful orange light to be reaching our eyes from both area C on the cube on the left, and area D on the cube on the right. The light from these two areas is physically identical, but we perceive the scene on the left to be brightly illuminated and area C to be reflecting this bright illumination, while we perceive the scene on the right to be dimly illuminated, and in this context area D is too bright to be merely reflecting light and is perceived to be emitting light. These perceptions do not arise from or require conscious thought: our visual system evidently arrives at them by some form of rapid, automatic, and unconscious comparison of responses to light throughout the scene.

Looking at the cube on the left, we perceive the light from areas A to B and to C to be increasingly bright and colourful, but we perceive this varying brightness and colourfulness to be imposed by (or resulting from) the illumination, rather than the cube itself having a different colour on each side. We perceive the cube as having the same vivid orange colour belonging to it, as if it were painted all over with the same paint. In the same way we perceive all of the lighter coloured tiles as being white in colour, even though the light they send to the eye is perceived to vary in brightness and (on the right) colour.

A colour perceived as belonging to an object is called an object colour. Objects perceived to be reflecting light, like the cube on the left, are said to have a non-luminous object colour, while objects perceived to be emitting light, like area D on the cube on the right, are said to have a luminous object colour.

Object colour reference: David Briggs, The Elements of Colour