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1328 Chapter 15: Lights and Cameras
In this example, the points in the n egative Z
direction are the same distance from the origin
as the corresponding p oints in the positive Z
direction,sothesameamountoflightshines
upward and downward. No point has a very large
X or Y component, either positive or negative, s o
less light is cast laterally from the light source.
IES Standard File Format
You can create a photometric data file in the IES
format using the IES LM-63-1991 standard file
format for photometric data. (IES stands for
Illuminating Engineering Society.) However,
only the information relevant to 3ds Max is
described here. For a complete description of the
IESstandardfileformat,seeIESStandardFile
Format for Electronic Transfer of Photometric
Data and Related Information, prepared by the IES
Computer Committee (h
ttp://www.iesna.org).
The l uminous intensity distribution (LID)
of a luminaire is measured at the nodes of a
photometric web for a fixed set of horizontal and
vertical angles. T he poles of the web lie along the
vertical axis, with the nadir corresponding to a
vertical ang le of zero degrees. The horizontal
axis corresponds to a horizontal angle of zero
degrees and is oriented par allel to the length of
theluminaire. Thistypeofphotometricwebis
generated by a Type C goniometer and is the
mostpopularinNorthAmerica;othertypesof
goniometr y are supported by the IES standard file
format but are not d iscussed here.
The photometric data is stored in an ASCII
file. Each line in the file must be less than 132
characters long and must be terminated by a
carri age return/line-feed character sequence.
Longer lines can be continued by inserting a
carri age return/line-feed character sequence. Each
fieldinthefilemustbeginonanewlineandmust
appear exactly in the follow ing sequence:
1. IESNA91
2. [TEST]thetestreportnumberofyourdata
3. [MANUFAC] the manufacturer of the
luminaire
4. TILT=NON E
5. 1
6. Theinitialratedlumensforthelampusedin
thetestor-1ifabsolutephotometryisusedand
the intensity values do not depend on different
lamp ratings.
7. A multiplying factor for all the candela values
in the file. This makes it possible to easily
scaleallthecandelavaluesinthefilewhen
the measuri ng device operates in unusual
units—for example, when you obtain the
photometricvaluesfromacatalogusinga
ruler on a goniometric diagram. Normally the
multiplyingfactoris1.
8. The number of vertical angles in the
photometric web.
9. The number of horizontal angles in the
photometric web.
10.1
11.The type of unit used to measure the
dimensions of the luminous opening. Use 1 for
feet or 2 for meters.
12.The width, length, and height of the luminous
opening. Currently , Lightscape ignores these
dimensions because you can associate a given
luminous intensity distribution with any of
the luminaire geometric entities supported by
Lightscape.Itisnormallygivenas000.
13.1.0 1.0 0.0
14.The set of vertical angles, listed in increasing
order. If the distribution lies completely in
the bottom hemisphere, the first and last
angles must be 0° and 90°, respectively. If
the distribution lies completely in the top
hemisphere, the first and last angles must be 90°