Photometrics

How to create and modify IES files

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and photometric webs.

You can use photometric webs to create custom luminous intensity distributions

(LIDs) . Use IES files to import manufacturer’s lighting specifications into your model.

Summary

In this chapter, you learn about:

•

Using photometric data

• Creating and editing photometric webs

•

The IES standard file format

• Using LID conversion utilities.

Using Photometric Data

You can interactively model any luminous intensity distribution (LID) for a luminaire using the Photometric Web editor. You can load and view photometric data files provided by various manufacturers into the photometric definition. You can also create your own using the Photometric Web editor.

About Photometric Webs

Photometric webs are used to represent general

LIDs. You can use LIDs in the definition of all three types of light sources: point, linear, and area sources.

To describe the directional distribution of the light emitted by a source, Lightscape approximates the source by a point light placed at its photometric center. With this approximation, the distribution is characterized as a function 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.

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9 Photometrics

This graphical representation of 3D lighting distribution is widely used in the lighting industry to describe the photometric characteristics of both lamps and luminaires. Lighting manufacturers often make this data available to design professionals for use in lighting analysis programs.

Goniometric Diagrams

Photometric data is often depicted using a goniometric diagram.

This type of diagram visually represents how the luminous intensity of a source varies with the vertical angle. However, the horizontal angle is fixed and, unless the distribution is axially symmetric, more than one goniometric diagram may be needed to describe the complete distribution. the photometric center, measured along a line leaving the center in the specified direction.

Goniometric diagram converted to a photometric web

Example 1: 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 light is emitted equally in all directions.

Goniometric diagram

Lightscape 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 luminaire.

The luminous intensity in any given direction is proportional to the distance between this web and

Isotropic distribution

Example 2: Ellipsoidal Distribution

In this example, the points in the negative Z direction are the same distance from the origin as the corresponding points in the positive Z direction, so the same amount of light shines upward and downward. No point has a very large X or Y component,

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