Viewing cone

When a visual display with non-vanishing size is seen by an observer, every point of the display area is seen from a different direction as illustrated in fig. 1. No two spots on the display are seen from the same direction. The larger the display is and the closer the observer is to the display the more the viewing direction varies over the surface area of the display.

Colloquially, the viewing direction is often called "viewing angle". This is an ill-chosen expression which should be avoided, because the viewing direction is specified by two polar angles: the angle of inclination, θ (measured from the surface normal of the display) and the azimuth angle, Φ, measured in the plane of the display as shown in figure 3.

In fig. 2, the eyeball represents the observer that is looking at a specific spot on the display which is identical to the origin of the polar coordinate system. The green arrow is the viewing direction (i.e. direction of observation). The viewing direction is specified by the angle of inclination, θ, measured from the surface normal of the display (blue vertical arrow) while the azimuth angle, Φ, is the angle that the projection of the viewing direction onto the surface of the display makes with the x-axis (red arrow). The projection of the viewing direction is shown here as the shadow of the green arrow. The azimuth angle Φ increases counterclockwise as illustrated in figure 3.

The multitude of directions, from which a display can be seen without artifacts and distortions that would render its intended use impossible (e.g. computerized office work, television, entertainment) is called the viewing cone (even though its shape might be that of a generalized cone).

The concept of the viewing cone has been introduced for the first time in the international standard ISO 13406-2:2001 "Ergonomic requirements for work with visual displays based on flat panels – Part 2: Ergonomic requirements for flat panel displays". This standard provides a classification for computer monitors with LCDs according to the range of viewing directions that can safely be used for the intended task (here: office work) without "reduced visual performance". The classification is according to "Viewing Direction Range Classes" with the "range of viewing directions" being equivalent to the viewing cone.

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