IES LM-81 PDF

IES LM-81 – Approved Method: Photometric Testing of Skylights and Tubular Daylighting Devices under Hemispherical Sky Conditions

Unlike electric luminaires, which require only one photometric test, skylights require a separate test to characterize their performance at different sun angles as well as a separate measurement to determine the sky conditions. This document provides 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. It 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. This document identifies 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.