This guide provides the IES required uniform method for determining and reporting the photometric characteristics of skylights and tubular daylighting devices. 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 (not recommended for devices with clear glazing). This guide 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.