28.2 Alternatively, the L2 AATCC Blue Wool Lightfastness Standard may be exposed at the specified temperature,humidity and selected conditions for 20士2 continuous light-on operating hours. After exposure, assess the exposed stanlord specimen, either instrumentally or compare to a L2 Standard of Fade for 20 AFU. When required, increase or decrease the wattage of the lamps, or the time of exposure, or both, and expose additional standard specimens until the change in color of the exposed standard meets one of the following criteria.