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Technical environment
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Contrast vision: what is contrast perception?

Contrast vision: brightly lit artworks in dark surroundings are seen more easily.

Contrast vision is the visual process of perceiving the difference in brightness (luminance) or colour between two objects, or between an object and its surroundings. To be able to see an object, it needs a sufficiently high contrast to its surroundings. This should ideally be at least 2:1. The lower the contrast, the more difficult it is to distinguish between two shapes.

Interesting facts about contrast vision:

Contrast vision is a function of vision closely related to visual acuity. Both functions, however, are not identical: contrast vision allows us to distinguish objects from each other to perceive them. Visual acuity on the other hand refers to how well we can recognize contours and details.

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Overview of the topic contrast vision:

What is meant by brightness contrast?

Whether an object is judged as bright or dark depends less on its absolute brightness (luminance), and more on its brightness in contrast to its surroundings. For example, a dimly lit object can seem bright in a dark room. The contrast in brightness is high. On the other hand, the object in bright surroundings but illuminated in the same way is hardly noticeable. The strongest light to dark difference in contrast vision is between a white and black surface.

Constructing hierarchies via brightness contrasts:

Contrast vision Contrast vision Contrast vision Contrast vision

Brightness contrast

 

The objects and the wall are given general lighting by wallwashers. Beams from individual spotlights add emphasis to the objects. A higher brightness contrast increases the level of accentuation.
When the brightness contrast of the ambient surroundings to the object is 1:2, a contrast can hardly be noticed. When the ratio is 1:5, a minimum brightness contrast is established between primary and secondary points of interest. A contrast of 1:10 brings out the difference very well. A brightness contrast of 1:100 detaches the object very strongly from its ambient surroundings but an unintentional dissection of the wall can arise.

Highlighting of objects on walls is a practice used in:

  • museums

  • exhibitions

  • trade-fair stands

  • sales rooms

What is contrast rendering?

Contrast rendering is a criterion for limiting reflected glare, and is thus a criterion of quality in lighting design, e.g. for the legibility of text. Contrast rendering is defined by the contrast rendering factor (CRF). This is the relationship between contrast of the visual task at a given illumination to the luminance contrast at a reference illumination.
Type of visual task Contrast rendering CRF level CRF mean value CRF minimum
mainly glossy materials, e.g. with graphic works high 1 1.0 < CRF > 0.95
Satin matt materials,
e.g. in offices and schools
medium 2 0.85 < CRF < 1.0 > 0.7
Work with matt material low 2 0.7 < CRF < 0.85 > 0.5

Is it possible to have no contrast?

We talk about loss of contrast when differences in luminance no longer exist. A distinction is made between two types of contrast loss:
  • Blackout: black objects in very dark to black surroundings can no longer be recognized.
  • Whiteout: white objects in white or very bright surroundings can no longer be seen in a differentiated way.

Winter sports people, especially skiers, are familiar with whiteout and they colloquially call it 'snow blindness'. Ground covered in snow, a bright horizon or snowfall can make it difficult or impossible to see your own surroundings. This is where contrast vision no longer functions.

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Further topics on seeing and perceiving

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