ANSI/IES LM-75 Approved method: guide to goniometer measurements and types, and photometric coordinate systems

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 undertest. Goniophotometric data are presented using various angular coordinate systems, and acquired using instruments of various constructions.
In addition to goniophotometers, goniocolorimeters exist,which use three-or four-channel colorimeters to measure color properties at a series of spherical coordinates, and goniospectroradiometers exist, which use array spectrometers to measure spectral properties at a series of spherical coordinates. Historically, each type of goniophotometer was developed to measure a light
source used in a specific application. Conventionally, measurement results for each type of light source were presented using a coordinate system that matched the specific application. Many current IES documents mention goniophotometers and coordinate systems. This document offers a complete explanation and provides harmonious definitions.

For luminaires, goniophotometers are used to
measure luminous intensity distributions using either the relative or absolute photometry method. Using relative photometry, the luminous intensity in each direction is derived by normalizing the indicated luminous intensity of the luminaire and then scaling it to the rated initial lumens of the bare lamp(s) used in the luminaire; thus, absolute photometric calibration of the goniophotometer is not necessary using this method. However, relative photometry does not work for certain solid-state lighting (SSL) products, where the source(s) cannot be separated from the luminaire. For
such products, absolute photometry, which requires a calibrated goniophotometer, shall be used.

This document provides definitions of goniophotometer types, spherical coordinate systems, and a general guide to goniophotometer calibration. Definitions presented herein are generally consistent with those in corresponding CIE publications [CIE 102′ and CIE 1212 ]. Differences or inconsistencies are noted.

LISUN following instruments fully meet ANSI/IES LM-75 Approved method: guide to goniometer measurements and types, and photometric coordinate systems:

LMS-6000 Portable CCD Spectroradiometer

LSG-2000 Goniophotometer with Rotating Mirror

LSG-1950 Goniophotometer for Automotive and Signal Lamps

LSG-1890B High Precision Rotation Luminaire Goniophotometer

LSG-1700 Rotation Luminaire Goniophotometer

LSG-1200A Compact Goniophotometer

LSG-1900B Near Field Moving Detector Goniophotometer