National Standard of Spectral Transmittance

National Standard of Spectral Transmittance

The National Standard of Spectral Transmittance ensures traceability and accuracy in measuring the transmittance of optically transparent materials. Since spectral transmittance is a dimensionless ratio (defined as the ratio of transmitted to incident radiant flux), it is not fundamentally linked to any of the seven SI base units.

Applications

Spectral transmittance measurement is widely used in:

• Chemical and pharmaceutical industries (quality control of transparent substances),
• Food industry and agriculture (analysis of liquid samples),
• Healthcare and medical research,
• Optical metrology (calibration of spectrometers and optical filters).

Measurement and Traceability

• Primary realization is based on the double aperture method, which ensures the accuracy of transmittance values through the controlled attenuation of radiation.
• The scale of spectral transmittance is transferred to Certified Reference Materials (CRM) for UV-VIS spectrometry.
• Other optical filters and cuvettes are calibrated using direct comparison with the NIST SRM 932 primary cuvette.
• The wavelength scale is referenced using well-defined emission lines from mercury, neon, and argon discharge lamps.

Equipment and Technical Implementation

The National Standard consists of:

• A UV-VIS molecular absorption spectrometer (Varian Cary 4E) with an operational wavelength range of 185–190 nm.
• A standard reference cuvette (NIST SRM 932) with a path length of 1 cm.
• The system operates based on Lambert-Beer’s Law, describing the relationship between spectral transmittance, concentration, and thickness of an absorbing substance.

The National Standard of Spectral Transmittance aligns with international metrology standards and undergoes regular validation through interlaboratory comparisons within COOMET, EUROMET, and CCPR, ensuring global comparability and reliability.

 

Documents for download

• Osvedčenie (certifikát) (pdf, 1.3 MB)