Principles - Whiteness is property of Luminous Objects. Whiteness is measured in terms of diffuse Reflectance, which is the ratio of reflected light measured at 90° after passing through a suitable filter and the incident light that is generally at 45° to the surface of the sample. With 45° Diffuse Reflectance head with Tristimulus green filter for whiteness of sample OR with head for brightness measurement OR for opacity measurement. Detailed specification as follows: Unless otherwise specified the Instrument is supplied with Green filter for whiteness measurement. Blue and amber filters are available at extra cost. The filters are interchangeable by the user as per the application.