Analyses - Generate IES Output

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Generate IES Output

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Description

Description

This dialog generates IES output. The intensity is calculated at directions on a polar grid according to the specified photometry type and written to a file in ANSI/IESNA LM-63-2002 format.

Navigation

This command can be accessed by selecting Analysis > Generate IES Output from the menu.

Controls

Control	Inputs / Description	Defaults
IES File Name	Name of IES output file. Type the filename directly or press the '...' button to select a filename by browsing with the file dialog.	Blank
Photometry Type
Type	Specifies the IES photometry type: A, B or C	Type C
Vertical Angles	Specifies the angular range in the vertical direction.	0 - 180 deg
Horizontal Angles	Specifies the angular range in the horizontal direction.	0 - 360 deg
# of angles	Specifies the number of angles at which to calculate the intensity. Note that some programs that read IES data require a sample at (0H,0V). To satisfy this requirement, specify an odd number of angles when using an angular range that doesn't end at (0H,0V).	19 V, 37 H
Spatial Orientation
Polar Axis	Specifies direction vector of the axis to use as the pole. Depending on the photometry type, this can be either the vertical or horizontal axis (see application notes for details)	(0, 0, 1)
Other Axis	Specifies the 'Other Axis' used to define the polar coordinate system. The meaning of this axis varies with photometry type (see application notes for details). If the axis entered is not perpendicular to the polar axis it will be used to calculate one that is. An error message will be reported if the 'Other Axis' is parallel to the polar axis.	(1, 0, 0)
Coord Sys	The coordinate system in which the polar and other axis are specified.	Global Coordinate System
Acceptance Cone Size
Set cone half-angle automatically to ensure overlap	If checked, the cone half-angle will be automatically set to ensure overlap of cones for adjacent sample directions at the equator. This guarantees all rays in the requested angle range will be binned at least once.	Checked
Intensity Values
Write intensity values as integers	If checked, the calculated intensities are rounded to the nearest integer when written to the IES file. This should be checked if the IES file is destined for use with software that requires integer intensities.	Unchecked
Cone Half-Angle (deg)	Specifies the size of the acceptance cone used for calculating intensity at each sample direction. See the discussion above for more information on this quantity's meaning.	10 deg
Convert ray powers to Lumens even though some source units are unknown	Applies photometric scaling to rays.	Unavailable when source units are known. Available and unchecked when source units are unknown.
Ray Selection Criteria
Table	Defines the rays included in the output.	AND All rays

OK	Output IES file and close dialog box.
Cancel	Discard file output and close dialog box.
Help	Access this Help page.

Application Notes

Calculation Details

The intensity calculation at a given direction is performed by binning rays with propagation directions within the specified cone half-angle of that given direction. The total flux collected along a direction is then divided by the solid angle that the acceptance cone subtends to give the intensity in that direction. One advantage of this approach is that each direction bin subtends the same solid angle, potentially giving more even statistics than an approach where the bin size varies with direction (e.g., polar grid bins).

If the cone half-angle is large enough, acceptance cones for adjacent polar direction samples can overlap and result in rays being collected in more than one direction bin. The intensity calculation will still be correct, but the adjacent intensity values will not be fully independent. By default, the cone size is chosen to be just large enough to ensure overlap of adjacent polar directions at the equator. While such a cone size guarantees that all rays (within the specified angular range) will be binned, it also produces a substantial overlap for directions near the poles.

To help illustrate this, the figure below shows the direction sphere with corresponding acceptance cones for directions marked by red dots.

Note that for adjacent polar directions near the equator the overlap is much smaller than for the same size cones near the pole. The net effect is that adjacent intensities near the poles will vary less than those near the equator.

The cone half-angle can be set so that some adjacent directions do not overlap, as illustrated below.

The intensities calculated for non-overlapping directions will be entirely independent. Rays with directions outside of all acceptance cones will simply not contribute to the calculation, and consequently the total number of rays binned may be less than the total number of rays within the angular range being calculated.

Photometry Types

These figures illustrate how angles and the orientation of axes relative to lamp illumination direction are defined for the different photometry types.

IES Type A

IES Type B

IES Type C

(Note: for Type C, the direction vector is along illumination direction.)

The ANSI/IESNA LM-63-2002 format is defined in "IESNA Standard File Format for the Electronic Transfer of Photometric Data and Related Information", LM-63-02, ISBN # 0-87995-178-8 (distributed by http://www.techstreet.com/).

Information on the coordinate systems used for the various photometry types can be found in "Goniophotometer Types and Photometric Coordinates", LM-75-01, ISBN # 0-87995-180-X (distributed by http://www.techstreet.com/).