Approved Method: Guide to Goniometer Measurements and Types, and Photometric Coordinate Systems

Guide to Goniometer Measurements and Types, and Photometric Coordinate Systems

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ANSI/IES LM-75-19
Document Type: Lighting Measurement and Testing (LM)

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SKU: ANSI/IES LM-75-19 Category: Tag:

Product Description

Approved American National StandardA 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
ISBN-13: 978-0-87995-010-1

Chapters:

  • 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
    6.0 Goniophotometers
    7.0 Calibration
    8.0 Integrated Measurements
    9.0 Stray Light Elimination and Correction

Citation Format:
Illuminating Engineering Society. ANSI/IES LM-75-19, Approved Method: Guide to Goniometer Measurements and Types, and Photometric Coordinate Systems. New York: IES; 2019.

CONTENTS

  • 1.0 Introduction and Scope
  • 1.1 Introduction
  • 1.2 Scope
  • 2.0 Normative References
  • 3.0 Definitions, including spherical coordinates
  • 3.1 apolar angle
  • 3.2 attitude, application
  • 3.3 attitude, design
  • 3.4 attitude, measurement
  • 3.5 azimuth angle
  • 3.6 CIE (A,α) Coordinate System
  • 3.7 CIE (B,β) Coordinate System
  • 3.8 CIE (C,γ) Coordinate System
  • 3.9 circumpolar angle (azimuth angle)
  • 3.10 coordinate system
  • 3.11 datum axis
  • 3.12 datum half-plane
  • 3.13 elevation angle
  • 3.14 first axis (of a light source)
  • 3.15 frame of reference
  • 3.16 frame of reference, application
  • 3.17 frame of reference, goniometer
  • 3.18 frame of reference, laboratory
  • 3.19 frame of reference, source
  • 3.20 half-plane of data
  • 3.21 half-plane, goniometric
  • 3.22 handedness (of a coordinate system)
  • 3.23 IES Coordinate System A (Y, X)
  • 3.24 IES Coordinate System B (H, V)
  • 3.25 IES Coordinate System C (V, L)
  • 3.26 left-handed coordinate system
  • 3.27 light source
  • 3.28 photometric center (of a light source)
  • 3.29 planar angle (angle in plane)
  • 3.30 right-handed coordinate system
  • 3.31 second axis (of a light source)
  • 3.32 spherical coordinates
  • 3.33 test axis (of a source)
  • 3.34 third axis (of a light source)
  • 3.35 tilt, measurement (of a source)
  • 3.36 zenith angle
  • 4.0 Laboratory, Goniometer, and Source frames of reference
  • 4.1 Frames of Reference Applicable to Goniophotometry
    4.1.1 Source Frame of Reference
    4.1.2 Goniometer Frame of Reference
    4.1.3 Laboratory Frame of Reference
    4.1.4 Application Frame of Reference
  • 4.2 Orientation with Respect to Gravity
  • 5.0 Coordinate Systems
  • 5.1 Spherical Coordinate Systems
  • 5.2 Defining a Spherical Coordinate System
  • 5.3 Example: The Geographic Coordinate System
  • 5.4 Standard Goniophotometric Coordinate Systems
    5.4.1 IES Coordinate System A (IES-A)
    5.4.2 IES Coordinate System B (IES-B)
    5.4.3 IES Coordinate System C (IES-C)
  • 6.0 Goniophotometers
  • 6.1 Type A Goniophotometer
    6.1.1 Instrument Design and Setup
    6.1.2 Instrument Operation
    6.1.3 Applications
  • 6.2 Type B Goniophotometer
    6.2.1 Instrument Design and Setup
    6.2.2 Instrument Operation
    6.2.3 Applications
  • 6.3 Type C Goniophotometer
    6.3.1 Instrument Design and Setup
    6.3.2 Instrument Operation
    6.3.3 Applications
    6.3.4 Design Variations
  • 6.4 Type D Goniophotometer
    6.4.1 Instrument Design and Setup
    6.4.2 Instrument Operation
    6.4.3 Applications
  • 7.0 Calibration
  • 7.1 Relative Photometry Method
  • 7.2 Absolute Photometry Method
    7.2.1 Luminous Intensity Calibration
    7.2.2 Illuminance Calibration
    7.2.3 Total Luminous Flux Calibration
  • 8.0 Integrated Measurements
  • 8.1 Method of Calculation
  • 8.2 Angular Frequency of Data Points
  • 9.0 Stray Light Elimination and Correction
  • 9.1 Stray Light and Its Sources
  • 9.2 Stray Light Elimination Techniques
    9.2.1 Limiting Field of View
    9.2.2 Reducing Reflected Light
    9.2.3 Use of a Light Trap
  • 9.3 Stray Light Correction Methodologies
    9.3.1 Using a Mask
    9.3.2 Handling of Negative Luminous Intensity Values
  • 9.4 Stray Light and Uplight Measurement
    9.4.1 Uplight Detection Threshold
    9.4.2 Criteria for Zeroing Uplight Readings
    9.4.3 Stray Uplight Test Setup
    9.4.4 Stray Uplight Test Procedure
  • 9.5 Reporting Zeroed Stray Uplight
  • Annex A – Coordinate System Conversion
  • Annex B – Zonal Constant Calculations
  • Annex C – Informative References