Vision: Seeing

Topics: ParthenonVision

Whilst perception is more widely defined as ‘to take in with the mind and senses . . . to apprehend . . . to become aware of by sight, hearing or other senses’.  We may see the space we are in through the light which falls upon its surfaces, but the way in which we perceive it calls upon a much more developed experience where sight is an important first step, but to which must be added hearing, smell and touch at the sensory level, as well as our emotional and intellectual reactions as formed by our age and experience.

  Visual Acuity  It is clear that the more difficult the task to be done, the more light is necessary. Although it is possible to perform at very low levels of light because of the human eye’s ability to adapt, if complex work is to be accomplished efficiently such levels would be inadequate – so higher light levels equate with more difficult tasks.

Glare Glare is the enemy of good lighting.

Buildings still suffer from the bad effects of glare – glare from natural light where the windows have been ill-conceived allowing too great a contrast between the view of the sky outside and the interior surfaces of the building; and glare from the artificial sources within. There are two basic types of glare: discomfort and disability and whilst the latter is the more important in terms of visual performance, the former may have a greater impression on the perception of a space. It is possible that both forms of glare may be experienced at the same time, and from the same light source, and it is necessary to understand the nature of the glare problem if it is to be remedied.

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The reflections of bright light sources on such tasks as glossy printed pages are known as veiling reflections because they reduce the contrast necessary for good visual performance. Glitter, or sparkle, is also a form of glare, but one that when associated with light sources, for example in a decorative pendant chandelier, can be acceptable. Ideally one would not place such a chandelier in a work situation.  The ancient Greeks realized that we do not perceive the world as it actually is. They found that when they built their early temples with straight lines, right angles, and uniform spacing of columns, the results were perceived not as they built them but distorted.

Consequently, the Greeks built later temples, like the Parthenon, in a very cleverly distorted manner so that they would be perceived as correct. In the Parthenon, the columns are all inclined inward to prevent the illusion that they are falling outward. The columns have a slight bulge (entasis) to counteract the illusion of concavity that characterizes columns with straight sides. Some columns appear bright because of the shaded wall behind them. Corner columns seen against the bright sky seem dark in comparison. Because the darker corner columns appear smaller and weaker than the brighter columns, the Greeks made the end columns stouter than the central columns. Relativity of brightness The absolute value of brightness, as measured by a photometer (light meter) is called luminance. A human being, however, judges the brightness of an object relative to the brightness of the surroundings. Since the Renaissance, painters have used this principle to create the illusion of bright sunshine.

The painter was able to highlight objects by creating a dark setting rather than by high illumination levels. The two isosceles triangles are exactly the same, yet they appear to have different reflectance factors because of the phenomenon of the relativity of brightness. To see the triangles as equal, cover the dark areas around the left triangle with two pieces of white paper  The abstract diagram shows this same principle. The middle gray tri-angles are identical in every way, including their reflectance factor. Their luminance, as measured by a photometer, will be the same, but their perceived brightness will depend on the brightness of the sur-rounding area. Another example, Car headlamps seem very bright at night but are just noticeable during the day. Although a meter would show the luminance to be the same, the brightness we perceive depends on the brightness of the headlamps relative to the overall lighting condition.

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Vision: Seeing. (2021, Dec 16). Retrieved from

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