Design Considerations
Last Update: October 30, 2010
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Task Visibility

A visual task is any object or area where the details need to be seen for the performance of an activity, such as identification and comprehension in the case of reading text or navigation in the case of walking through a corridor.

The following subsections discuss various factors of task visibility and how they play out in common interactions between people, architecture and light. Topics reviewed are various types of glare, reflections and shadows and the effects that contrast variability and surface changes can have on visibility.

Details of Task Visibility
Facial recognition is another example of a visual task. Task visibility is dealing with center focus clarity (foveal vision) or visual acuity at photopic vision conditions. For more information on task visibility see the Visual Performance section in Health & Performance.
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Disability Glare
Disability glare is glare that interferes with seeing the visual task due to light scatter within the eye creating a luminous veil (a haze of light) in the field of view, or in the case of night-time driving it may exhibit as starbursts, comets or halos.
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Reflected Glare
Just as disability glare creates an obscuring luminous veil in the eye, light striking a reflective surface, particularly a specular or semi-specular one, can created an obscuring luminous patch, called a veiling reflection, on that surface as viewed by the observer.
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Source/Task/Eye Geometry
Source / Task / Eye Geometry is the vector path of the light from the source to the eye in relation to the task. This relationship can either enhance or reduce the viewer’s ability to see the visual task.
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Intrinsic Material Considerations
Intrinsic material characteristics of the task material will impact the visibility and comfort of performing the task.
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Shadows affect visibility by impacting contrast. Body shadows are created when a part of the viewer’s own body is located between the light source and the visual task so that a shadow is thrown onto the task area, obscuring the task.
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Peripheral Detection
Peripheral detection refers to the eye’s ability to sense and recognize objects outside the center of view.  Lighting which enhances peripheral detection can provide a sense of security. Both light distribution and color appearance influence a person’s ability to detect objects and people in the periphery.
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