Spectral reflectance measurements
Standard measurements are made on a high quality commercial scanning spectrophotometer whose instrument scales are traceable to national standards. NPL can measure the regular (specular) reflectance of front surfaced mirrors using a VW specular reflectance accessory. This accessory has an angle of incidence on the sample of 7°.
Measurements can be made over the wavelength range 200 nm to 2500 nm. The bandwidth is typically 1 nm. Reflectance data are usually reported at 10 nm intervals. NPL can supply reference front surface mirrors or can measure mirrors supplied by the client. The minimum sample size is 20 mm x 30 mm and the maximum size is 150 mm x 130 mm.
The calibration of back-surface mirrors using the UW accessory may be possible, but it depends on the thickness of the cover glass. Thicker back-surface mirrors can be measured using a spectrophotometer with an integrating sphere accessory.
Measurements at other angles of incidence and collection are possible using one of NPL’s reference goniometric instruments. Other reflectance properties, such as gloss, can also be measured.
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