Use Blue Wool Lightfastness Standard specimens to calibrate and verify lightfastness testing as specified in applicable AATCC Test Methods. Measure 20 AATCC Fading Units (AFU) (85 kJ/m2nm @ 420 nm) or 5 AFU (21 kJ/m2nm @ 420 nm). L2 is approved for use in place of L4 for 20 AFU tests. AATCC L2 Blue Wool Lightfastness Standard is called out as a weathering reference material in SAE J2412-2004. SAE is an independent organization, and questions related to SAE standards must be directed to SAE.