Fluorescent Brightener Whiteness Index Saturation Limit

Both the saturation constant and the greening penalty are fitted to a specific brightener on a specific substrate and must be recovered by running a dose ladder and measuring CIE whiteness and tint on your own goods — they are not transferable between brightener classes or between cotton and polyester. The single whiteness number also hides the tint deviation, which is what an observer actually objects to; a fabric can hold its whiteness index and still look visibly green, so judge a ladder on tint as well. Whiteness measurement is itself illuminant-dependent, since the fluorescence needs UV in the source, and a result read under one instrument condition will not reproduce under another.