# e-ILV

The e-ILV provides free access to all the terms and definitions contained in the international standard CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition.

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# 17-25-085

angular subtense

α

angle subtended by a real or apparent source at a given point in space

Note 1 to entry: The point in space could be the eye of an observer or a point of measurement or any other defined point.

Note 2 to entry: Subtended angles are denoted by the full included angle, not the half angle.

Note 3 to entry: The light output of a source will often be modified by the incorporation of lenses and mirrors as projection optics, in which case the angular subtense of the apparent source can differ from the angular subtense of the physical source.

Note 4 to entry: The angular subtense of a non-symmetrically-shaped source is determined by the arithmetic mean of the maximum and minimum angular dimension of the source.

Note 5 to entry: The angular subtense is expressed in radian (rad) or degree (°).

Note 6 to entry: This entry was numbered 17-42 in CIE S 017:2011.

Publication date: 2020-12