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Photometric Webs 1327
Goniometric Diagrams
Photometric d ata is often depicted using a
goniometric diagram.
Goniometric diagram of a web distribution
This ty pe of diagram visually represents how
the luminous intensity of a source varies with
the vertical a ngle. However, the horizontal
angle is fixed and, unless the distribution is
axially symmetric, more than one goniometr ic
diagram may b e needed to describe the complete
distribution.
Photometr i c Web
The photometric web is a three-dimensional
representation of the ligh t distribution. It extends
the goniometric diagram to three dimensions, so
that the dependencies of the luminous intensity
on both the vertical and horizontal angles can
be exam ined simultaneously. The center of the
photometric web represents the center of the light
object.
The luminous intensity in any g iven direction is
proportional to the distance between this web and
the photometr ic center, measured along a line
leaving the center in the specified direction.
Example 1: Isotropic Distribution
Example of isotropic distribution
A sphere centered around the origin is a
representation of an isotropic distribution. All the
points in the diagram are equidistant from the
center and therefore lig ht is emitted equally in a ll
directions.
Example 2: Ellipsoidal Dist ribut ion
Example of ellipsoidal distribution