AATCC TM148-1989, Light Blocking Effect of Curtain Materials, was discontinued in 1994. During the time of its discontinuance, it was found that a standard laboratory sphere spectrophotometer used in transmission mode could be used to measure the light blocking effect of textiles used in end uses such as partial and full blackout curtains in both residential and contract applications. This method uses spectrophotometric measuring equipment that provides precise, reproducible and traceable light measurements. These instruments are currently in wide industrial use. This test method is intended to spectrophotometrically measure the light blocking properties of window covering textiles against light passing through them and being seen by a standard observer on the darkened side of the textile (typically a curtain or drape). This method is applicable to all types of fabrics, including knits, wovens, and non-wovens, as well as to fabrics taken from end product items. However, it is not recommended for mesh structures with mesh holes greater than 3 mm across.