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Photometric Webs 1171
Ph otometr ic Webs
Lightthatusesaphotometricweb
Aphotometricwebisa3Drepresentationof
the light intensity distribution of a light source.
This directional light distribution information is
stored in a photometric data file in the IES format
using the
IES LM-63-1991 standard fi le format
(page 2–1172)
, or in the LTLI or CIBSE formats
for photometric data. You can load photometric
data files provided by var ious manufacturers as
web parameters (page 2–1199) .Thelighticon
represents the photometric web you select.
To describe the directional distr ibution of the light
emitted by a source, 3ds Max appro ximates the
source by a point light placed at its photometric
center. With this approximation, the distribution
is characterized as a func tion of the outgoing
direction only. The luminous intensity of the
source for a predetermined set of horizontal and
vertical angles is provided, and the system can
compute the luminous intensity along an arbitrary
direction by interpolation.
Goniometric Diagrams
Photometric data is of ten depicted using a
goniometric diagram.
Goniometric diagram of a web d istribut ion
This type of diagram visually represents how
the luminous intensity of a source varies with
the vertica l angle. However, the horizontal
angle is f ixed and, unless the distribution is
axially symmetric, more than one goniometric
diagram may be needed to describe the complete
distr ibution.
Photometr i c Web
The photometric web is a three-dimensional
representation of the light 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 examined simultaneously. The center of the
photometric web represents the center of the light
object.
The luminous intensity in any given direction is
proportional to the distance between this web and