Visual Performance

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Introduction

Testing visual performance 1.jpg
Testing visual performance 2.jpg

Lighting is an important influence on visual performance. A visual task describes any situation when people are interacting with objects in a space, e.g. reading, playing football or any other task. The importance of accuracy is depending on the task. Visual performance is influenced by illuminances, luminances, contrasts, color differences, size, movement and time. E.g. contrast and color difference between a task detail and the background are crucial for visibility of the object.

The size of the task and the distance from the viewer are influential, the time available to perform the task, as well as the question if the task involves movement and if yes in what speed. Additionally color temperature of light affects the accuracy of the visual performance as well as the visual experience.

Contrast.jpg
Size.jpg

Contrast is a parameter of visual performance defining the combination of light and dark areas, i.e. black letters on a white page or a shadowy spot of dirt on a colored floor. Contrast is affected by the source-task-eye geometry, glare, shadows and surface properties.

An increase in size of the visual task improves its visibility, influenced by the physical size of the task, the viewer’s distance, and the angle of view. E.g. a text written in a normal size font is can be read from close-by but not from a larger distance.

Movement affects visual performance as well. The accurate detection of a moving object depends on the predictability of the movement, the contrast, luminance and the size. The age of the observer is another influence on visual performance since the eyes of older people need higher illumination levels to achieve the same level of visual acuity than those of younger people. Additionally they have a higher risk to misread heights and distances. This influence can be balanced with glasses to some extent, but should be taken into account when designing for elderly people.

Generally daylight has a greater probability of maximizing visual performance than most electric lighting systems because of higher lighting levels and a spectrum that ensures excellent color rendering.



Section Key Resources
  • P. Boyce, C. Hunter, O. Howlett, (2003): The Benefits of Daylight Through Windows, Lighting Research Center, Rensselaer Polytechnic Institute, USA, http://www.lrc.rpi.edu/programs/daylightdividends/pdf/DaylightBenefits.pdf, accessed September 2010
  • Mahnke, F.H. (1996): Colour, Environment and Human Response, Van Nostrand Reinhold, New York, USA
  • Boubekri, M. (2008): Daylighting, Architecture and Health, Building design strategies, Elsevier Architectural Press, Oxford, UK
  • Illuminating Engineering Society of North America (xxxx): Light+Design, A Guide to Designing Quality Lighting for People and Buildings, IES DG-18-08
  • Fördergemeinschaft Gutes Licht, Lichtwissen 19, Impact of Light on Human Beings, Licht.de, Frankfurt, Germany
  • Phillips,D. (2000): Lighting modern buildings, Architectural Press, Oxford, UK
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Lead Author(s): Aris Tsangrassoulis

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