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Approved Method: Photometric Testing of Skylights and Tubular Daylighting Devices Under Hemispheric Sky Conditions

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ANSI/IES LM-81-20(R2023)
Document Type: Lighting Measurement and Testing (LM)

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SKU: ANSI/IES LM-81-20(R2023) Category:

Product Description

Approved American National StandardLearn the IES recommended uniform method for determining and reporting the photometric characteristics of skylights and tubular daylighting devices that incorporate a means to diffuse the natural hemispherical daylight as the daylight passes through the daylighting system. LM-81 describes the procedures followed and the precautions observed in obtaining uniform and reproducible measurements of tubular daylighting devices and skylights with glass or plastic glazing; as well as identifying the components and the structure type needed to adequately measure daylighting devices. The procedures, calibration of the equipment, and determination of sun angles and sky conditions are also discussed.

Page count: 17 pages
Publisher: Illuminating Engineering Society (2023)
SKU: ANSI/IES LM-81-20(R2023)
ISBN-13: 978-0-87995-239-6

Chapters:

  • 1.0 Introduction and Scope
    2.0 Test Distance
    3.0 Goniophotometer Basic Construction
    4.0 Photometer Structure
    5.0 Calibration
    6.0 Sky Conditions
    7.0 Testing Procedures
    8.0 Testing Procedure
    9.0 Limitations of Skylight Photometry

Citation Format:
Illuminating Engineering Society. ANSI/IES LM-81-20(R2023), Approved Method: Photometric Testing of Skylights and Tubular Daylighting Devices Under Hemispheric Sky Conditions. New York: IES; 2023.

CONTENTS

  • 1.0 Introduction and Scope
    • 1.1 Introduction
    • 1.2 Scope
  • 2.0 Test Distance
  • 3.0 Goniophotometer Basic Construction
    • 3.1 Small Aperture (Tubular) Goniophotometer
    • 3.2 Skylight Goniophotometer
    • 3.3 Electrical/Electronic System
    • 3.4 Amplifier Box
    • 3.5 Electronic Interface Box
    • 3.6 Computer Interface Board
    • 3.7 Vertical Angular Planes (Step Motor)
    • 3.8 Data Collection Speed
    • 3.9 Automated Goniophotometer
  • 4.0 Photometer Structure
  • 5.0 Calibration
    • 5.1 Periodic Calibration and Accuracy
    • 5.2 Data Reduction
    • 5.3 Stray Light
  • 6.0 Sky Conditions
  • 7.0 Testing Procedures
    • 7.1 General Test Conditions
    • 7.2 Daylight Device Positioning
    • 7.3 Sun Angles
    • 7.4 Selection of Angles for Photometric Measurements
    • 7.5 Testing Start Time in Relation to Sun Angle Times
    • 7.6 Reporting
  • 8.0 Testing Procedure
  • 9.0 Limitations of Skylight Photometry