Measuring reflectance in the ultraviolet, visible and near-infrared (UV-vis-NIR) range
We can provide reflectance calibrations in the three CIE standard measurement geometries:
- Specular included (8°:di)
- Specular excluded (8°:de) using an integrating sphere accessory
- 0°:45°a geometry using a ring collector accessory
Calibrations can be made either on transfer standards supplied by NPL or on customers' own samples. Most calibrations are UKAS-accredited.
Measurements are routinely made over the wavelength range 380 nm to 2500 nm, with data reported at 5 nm intervals over the spectral range 380 nm to 1300 nm and at 100 nm intervals over the spectral range 1400 nm to 2500 nm. Colorimetric data for both the 2° and 10° degree CIE standard observers and for illuminants A, C and D65 are also reported for measurements over the spectral range 380 nm to 780 nm.
Near-infrared diffuse reflectance measurements can also be carried out to defence standards, including measurement of camouflage materials and enamelled samples.
We can measure the regular (specular) reflectance of front-surfaced mirrors using a VW specular reflectance accessory, which has an angle of incidence on the sample of 7°. Measurements are traceable to the NPL reflectance scale and can be made over the wavelength range 200 nm to 2500 nm. The bandwidth is typically 1 nm and data are usually reported at 10 nm intervals. We can supply reference front surface mirrors or can measure mirrors supplied by the client.
Other facilities at NPL can be used to make measurements that are not covered by routine calibration services. These could be measurements of transmittance, reflectance or radiance factor at higher accuracy than our normal calibration services, radiance factor or bidirectional reflectance distribution function (BRDF) at non-standard angles of incidence and collection.