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Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. While relatively simple in concept, determining the reflectance or transmittance involves careful consideration of the geometrical and spectral conditions of the measurement. We maintain the national scales for reflectance and transmittance in the ultraviolet, visible, and near-infrared spectral regions (250 nm to 2500 nm).


Our primary objective is the dissemination of the national scales for reflectance and transmittance from 250 nm to 2500 nm. NIST serves as the nation's primary source for these measurements. Our reflectance and transmittance measurements support the measurement infrastructure of communities involved in optics, photonics, color technology, instrument manufacturing, pharmaceutical, healthcare, coatings manufacturing, and remote sensing. NIST also supports the measurement services of our nation's military standards laboratories and interacts with its peers at nation metrology institutes through international intercomparisons.

NIST continually strives to improve its capabilities for providing these measurements and add to the general knowledge by performing research on related topics. For reflectance, we have been working in recent years to improve our measurement capabilities for bidirectional reflectance in the shortwave infrared. Our research has focused primarily on characterizing reflective materials. NIST is also developing the next-generation reflectance facility. For transmittance, we are working to improve our uncertainties in the ultraviolet.


Calibrations for reflectance and transmittance are offered through NIST Calibration Services. The measurement parameters for these calibrations are customizable, within the limits of our capabilities. Pricing is based on actual costs, labor and time, the number of test items, and the number of data points. Following the calibration, a calibration report is issued, which includes the calibration values and uncertainties for the customer-supplied test item(s). For information can be found at Optical Properties of Materials Measurements or contact Catherine Cooksey for a nist-quote.

Wavelength Standards

NIST previously offered calibration of holmium oxide glass under the Service IDs 38050C and 38051C. However, based on NIST's extensive experience with holmium oxide glass and its long-term stability, NIST no longer sells or recertifies this standard. These standards have shown insignificant spectral variation from batch to batch and from one manufacturer to another. More information can be found in the paper, Holmium Oxide Glass Wavelength Standards. Transmittance and absorbance data from this paper can be download as an Excel file (404 kB).

Major Accomplishments

Created November 13, 2009, Updated April 23, 2019