Light can play tricks on the mind. Two people can perceive the colour of an object very differently, depending on how they are viewing it. For instance, if you go into a room that is illuminated blue, the cone receptors on your retina compensate within 10 to 15 seconds, making the blue appear less intense. If a second person enters the blue room, it takes time for their retina to adjust so they will, at least for a short time, have a different colour experience from you. Alternatively, if the lighting is suddenly changed from blue to white, everything in the room takes on an orange hue until your eyes readjust.
How an individual sees colour is impossible to measure directly. The closest psychophysicists have managed to get is by asking people to compare light of different wavelengths and intensities, and then seeing how the subjective experience they report correlates with the physical properties of the light.
Danish-born artist Olafur Eliasson is fascinated by how we perceive colour, and brings such experiments to a wider audience by building installations in galleries. The picture here shows one of these. Rings of coloured filters turn in front of a light source, causing coloured light to whirl around a darkened room. It is a bit like the light bouncing around the dance floor from a rotating mirrorball, but it addresses a fundamental question about the nature of perception. We only see objects by virtue of the light that bounces off them. Yet we are able to recognise these objects for what they are even when the wavelength or intensity of the light that illuminates them varies wildly. The brain compensates for this variation to provide us with a coherent, meaningful notion of the world.
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鈥淐olour doesn鈥檛 exist in itself but only when looked at,鈥� says Eliasson, whose Your Uncertainty of Colour Matching Experiment runs at the Ikon Gallery in Birmingham, UK, from 26 July to 17 September 2006.