When used with industrial and commercial products, there is more than one definition of “opacity” as an optical property.
Contrast Ratio Opacity (OP) measurements quantify how close to opaque a near-opaque material is.
The measurement is a two-part program metric where the CIE Y (luminance or brightness) value is first measured the sample backed by a black background, followed by a second measurement of the Y value of the sample backed by a white background. The resulting fraction is expressed as Y%, calculated as follows:.
As Y Brightness is a colorimetric value calculated based on a CIE illuminant/’observer condition, this must be specified and reported. The illuminant/observer choice will vary depending on the industry – A/2 (automotive), C/2 (historical and default choice), D65/2 (printing) and D65/10 (often used in current color measurements). As Opacity is a ratio, the results will be nearly identical for any of these illuminant/observer conditions.
Typical applications where contrast opacity is an important appearance characteristic are coating drawdowns and single sheets or layers of paper, plastic and textiles.
The primary appearance concern is lot-to-lot consistency in a material that is inherently not quite opaque.
Industrial References for Contrast Ratio Opacity
Visual Methods for coatings and also applied to plastic sheets
ASTM D344 Test Method for Relative Hiding Power of Paints by the Visual Evaluation of Brushouts
Instrumental methods for coatings and also applied to plastic sheets and plaques:
ASTM D2805 Standard Test Method for Color for Hiding Power of Paints by Reflectometry
Instrumental methods for paper sheets:
ASTM D589 Test Method for Opacity of Paper is similar to TAPPI T425
DIN 53146: Publication date:2000 Testing of paper and board – Determination of opacity
ISO 2471 Paper and board – Determination of opacity (paper backing) — Diffuse reflectance method is similar to TAPPI T519
PAPTAC E.2U Opacity of Paper – Contrast Ratio
TAPPI T425 om-01 Opacity of Paper (15/d Geometry, Illuminant A/2 Degrees, 89% Reflectance Backing and Paper Backing)
TAPPI T519 om-02 Diffuse Opacity of Paper (d/0 Degrees Paper Backing)
FAQ: I see Opacity Y in your program but not Opacity Spectral that we have in a competitive software. We use Opacity Spectral, is there anyway to get it?
ANS: The typical opacity is contrast ratio Opacity Y. I am aware of Spectral Opacity but there is more than one type. Do you have a definition that you are looking for?
FAQ: This is all I could find in any reference documents.
Percent Opacity = (Black “L” Value/White “L” Value) x 100 (OPAC).
ANS: What you are calling Spectral Opacity is really a non-standard version of colorimetric contrast ratio opacity.
The Hunter L (lightness) value comes directly from Y Brightness, so you should get the same Opacity % contrast ratio from either using Hunter L Lightness or CIE Y Brightness.
My recommendation would be use the standard Contrast Ratio Opacity (Y) per ASTM D2805.