The National Physical Laboratory (NPL) realises and maintains the primary standards of measurement for the United Kingdom. In colorimetry and spectrophotometry these are realised through reference instruments for the measurement of regular and diffuse transmittance, regular and diffuse reflectance, surface colour including fluorescent materials, gloss and haze. Recent developments include a novel method of measuring the uniformity of integrating spheres and a high speed spectrofluorimeter using a diode array spectrometer.Traceability of measurements to industry is provided through a calibration service for customers materials and the issuing of NPL calibrated transfer standards. These include neutral density filter transmittance standards, ceramic colour standards and crystal wavelength standards. The programme includes studies of thermochromism, translucency and temperature coefficients of transfer standards. Research into visual scales is carried out using computer controlled displays and the NPL Visual Research Colorimeter. This includes studies of photometric scales in the scotopic, mesopic and photopic regions using brightness matching and flicker photometry. A calibration service for visual displays has also been developed.

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