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NPL has two measurement methods available for gloss measurements according to ISO 2813 and ASTM D523, both using a tungsten source filtered to provide a close match to CIE Standard Illuminant C and a detector which provides a good match to the CIE photometric standard spectral efficiency function, V(λ):

Method 1: uses a commercial bench gloss meter to compare samples at 20°, 60° and 85° against in-house reference standards traceable to the NPL National Reference Reflectometer. The best measurement capability yields an uncertainty of 1 GU, though only for a very limited set of samples and measurement conditions.

Method 2: measures samples directly on the NPL National Reference Reflectometer that is used to realise the NPL gloss scale. This method generates results for any measurement geometry. The best measurement capability yields an uncertainty of 1 GU over a far wider range of samples and measurement conditions than possible by method 1. Experiments conducted with a wide range of commercial glossmeters and gloss transfer standards have shown that the range in values reported by different gloss meters increases significantly as the gloss of samples differs from the calibration points of (nominally) 100 and 0 GU. Readings for semi-gloss standards (nominally <60 GU) show particularly large variations from one instrument to another. For these reasons, method 1 results for samples differing significantly from the NPL in-house standards will carry a high measurement uncertainty. Some customers require proof that sample gloss is below a certain value. Such samples are often considerably less than the specified value so method 1 would suffice. If better measurement uncertainty is required, or values are needed for any geometry other than at 20°, 60° and 85°, method 2 will be necessary.

Contact

Customer Service tel: +44 20 8943 6151
E-mail: optical_enquiries@npl.co.uk