The most widely accepted whiteness calculation in the Paper Industry is the following formula which is defined in TAPPI, ISO, ASTM among others.
Keep in mind that these equations should be used only for specimens with
40 < WI < (5Y-280) and -4 < T < +2
where, T is the tint value that complements the whiteness calculation.
Some companies use whiteness measurement as a production specification and others use it in marketing. How do you use whiteness measurement?