National Physical Laboratory

Detector responsivity

This facility establishes the response of a detector across a range of wavelengths, whether that be in the Ultraviolet, Visible or Infrared.

Spectral Responsivity Facility
Spectral Responsivity Facility

NPL's spectral responsivity facility disseminates the response of a working standard from the known behaviour of a transfer detector. The accuracy of the measurement depends on the waveband of interest, and therefore the working standard used. Carefully chosen working standards can be characterised to provide the best possible response at the required wavelength.

The spectral responsivity facility uses a monochromator to select a narrow waveband of several nanometres, from the continuum between 200 nm and 20 µm. The facility is accredited under UKAS over the range of 200 nm – 1800 nm.

Special modifications are required for use at infrared wavelengths. Gold-coated optics are preferable as good reflectors at this range, with similar adjustments occurring to the gratings of the monochromator. Alternatively, a separate specially designed monochromator can be used, optimised for performance in the infrared.

NPL has years of experience in selecting the appropriate detector for the spectral region. Thermal detectors, which have a flat response, are used to provide a relative spectral response scale from the ultraviolet to the far infrared. Trap detectors provide the absolute link to the primary standard. Detectors are increasingly used to improve industrial processes and further the development of new products.


The spectral responsivity facility uses a double subtractive monochromator, with supporting optics and electronics contained in a light tight box. An automated stage allows four detectors to be measured simultaneously.

Detectors relevant to the required range of use can be provided, along with recommendations and advice for detector use.

Operating details



Tungsten lamps, Glow bar sources, Argon and Xenon arc lamps

Spectral range

200 nm to 20 µm


Adaptable detector optics to provide f/4 to > f/8 configurations
depending on the detector being measured

Contact us for further information

Call the Customer Service team on: 020 8943 6151

Last Updated: 30 Jul 2018
Created: 19 Jun 2007


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