What is Hunter Whiteness Index?

Hunter Whiteness Index [WIH]

There are at least half a dozen whiteness indices in use today, and a similar number of legacy whiteness indices no longer in use. There are subtleties among them and it is important to know the forms of these whiteness metrics and conditions for which they are derived for. In general, a material will exhibit high whiteness if the material reflectance has high and even reflectance, near 100%, across the visible spectrum.

There is a 1942 version and a 1960 version of the Hunter Whiteness Index. The more commonly known Hunter Whiteness Index was defined in 1960 based on the Hunter L, a, b scale for C/2 conditions.

Hunter Whiteness Index (1942)

WIH = 100 – {[220 (G – B) / (G + 0.242 B)]2 + [(100 – G)/2] 2 }1/2   (C/2)

Hunter Whiteness Index (1960)

WIH = L – 3b (Hunter L, a, b C/2) = 10 (Y – 21)1/2 (Y – 0.847 Z)Y1/2 (C/2)

For a PRD Perfect White of 100% reflectance across the visible spectrum, WIH will have a value of 100, falling off sharply as the sample color gets darker or more yellow.

A couple of notes…

• The Hunter WI 1960 metric has been seen in documentation as “Hunter 60”.
• Stensby Whiteness Index is derived from the Hunter Whiteness Index and shows a preference for redder whites (European preference).

WIStensby = L – 3b + 3a (Hunter L, a, b C/2)

FAQ – Why we don’t include the Hunter Whiteness Index in current HunterLab software?

Working with multiple whiteness indices all of which quantify the degree of whiteness just adds confusion to customers in reporting and communication.

While the Hunter Whiteness Index works well enough, there are more modern whiteness indices supported by industrial test methods that work just as well or better in quantifying whiteness.

We would recommend Whiteness Index E313 per ASTM E313 Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates www.astm.org typically calculated for C/2 or D65/10 conditions. The ASTM E313 test method mentions Hunter WI as one of the progenitors of ASTM E313. WI E313 C/2 or D65/10 is currently the most commonly used and reported whiteness index in industry.