A goniophotometer is a photometer for measuring the directional light distribution characteristics of sources, luminaires, media and surfaces. A goniophotometer records photometric readings at a series of spherical coordinates to define a web of photometric data surrounding the item under test. Goniophotometric data are presented using various angular coordinate systems, and acquired using instruments of various constructions. Many current IES documents mention goniophotometers and coordinate systems. This document offers a complete explanation and provides harmonious definitions. This document provides definitions of spherical coordinate systems and goniophotometer types used to measure light sources. It does not address the use of goniophotometers to measure media or surfaces. The operating principles behind each type of goniophotometer are addressed, and a general guide to goniophotometer calibration, stray light elimination, and stray light correction is presented. A methodology for zeroing data when measuring upward light is also provided. In addition, the correspondences between relevant IES and CIE definitions are described.
Page count: 28 pages
Publisher: Illuminating Engineering Society (2019)
SKU: ANSI/IES LM-75-19
- 1.0 Introduction and Scope
2.0 Normative References
3.0 Definitions, including spherical coordinates
4.0 Laboratory, Goniometer, and Source frames of reference
5.0 Coordinate Systems
8.0 Integrated Measurements
9.0 Stray Light Elimination and Correction
Illuminating Engineering Society. ANSI/IES LM-75-19, Approved Method: Guide to Goniometer Measurements and Types, and Photometric Coordinate Systems. New York: IES; 2019.