What is whiteness?

WHAT IS WHITENESS?

WHITE IS A COLOR TOO. ALTHOUGH IT IS ACHROMATIC, IT IS STILL A COLOR IN THE COLORIMETRIC SENSE. WITH AN IDEAL WHITE, ALL THE INCIDENT LIGHT IN THE 400-700 NM RANGE IS REFLECTED. THIS "IDEAL WHITE" IS, HOWEVER, PURELY A THEORETICAL QUANTITY. BARIUM SULPHATE, WHICH WAS ONCE WIDELY USED AS A WHITE STANDARD, "ONLY" GIVES AN AVERAGE REFLECTION OF 98% ACROSS THE VISIBLE SPECTRUM.

"WHITENESS THAT IS, HOW WHITE A MATERIAL IS IS A YARDSTICK FOR QUALITY FOR MANY TYPICALLY WHITE MATERIALS SUCH AS PAPER OR TEXTILES. THE "WHITENESS" OF A MATERIAL CAN ADMITTEDLY COME VERY CLOSE TO AN IDEAL WHITE IF THE MATERIAL IS BLEACHED, THUS DESTROYING THE COLOR PIGMENTS THAT ABSORB LIGHT. BUT IF A WHITE NEEDS TO BE "BRIGHT" THEN OPTICAL BRIGHTENERS ARE USED TO OBTAIN A "PERFECT" WHITE. THESE OPTICAL BRIGHTENERS, WHICH ARE ALSO FOUND IN EVERYDAY LIFE IN WASHING POWDERS AND TOOTHPASTES, FOR EXAMPLE, HAVE PROPERTIES THAT ENABLE THEM TO ABSORB RADIATION IN THE UV RANGE (<400> 400 NM). MATERIALS THAT HAVE BEEN TREATED WITH AN OPTICAL BRIGHTENER CAN THEREFORE HAVE A REFLECTION VALUE OF >100%. THESE MATERIALS APPEAR TO BE "BRIGHT" WHITE.