National Physical Laboratory

Spectral Irradiance and Radiance

Tungsten filament or halogen lamps can be calibrated, with UKAS accreditation, for spectral irradiance.


This includes the calculation of chromaticity coordinates and correlated colour temperature from the spectral data. Specifications as follows:

  • Nominal power rating: 50 W to 1000 W
  • Correlated colour temperatures (CCT): 2600 K to 3250 K
  • Wavelength range: 250 nm to 2500 nm

For customers requiring the lowest possible uncertainties a UKAS accredited service is now available for the calibration of irradiance standard lamps against the NPL ultra high temperature blackbody. This is the reference source used to calibrate NPL's own irradiance standard lamps.

A UKAS service is also available for the measurement of relative and absolute spectral radiance of tungsten based sources. Specifications as follows:

  • Lamp or integrating sphere
  • Broadband or filtered
  • Wavelength range: 300 nm to 2500 nm

Measurements are carried out on our Spectral Irradiance and Radiance Primary Scale facility, which utilises a double monochromator system with a suite of detectors, mounted on a moving stage. Calibrations are carried out against a series of NPL standards traceable to the NPL2010 absolute irradiance/radiance scale or against the reference blackbody. Up to 4 lamps or 2 radiance sources can be calibrated at a time on our automated system.

Calibrations of either relative or absolute irradiance/radiance can be made at fixed intervals of 10 nm from 250 nm to 1000 nm and 50 nm from 1000 nm to 2500 nm. Results can be interpolated to provide data at other intervals.

Facility Details


250 nm to 2500 nm for irradiance, 300 nm to 2500 nm for radiance


Tungsten and tungsten halogen sources, integrating sphere based radiance sources


PMT, Silicon, InGaAs and InSb

Calibration Sources

Ultra High Temperature Blackbody, Polaron and FEL sources

Contact us for further information

Call the Customer Service team on: 020 8943 6151

Last Updated: 28 Apr 2017
Created: 10 Aug 2009


Please note that the information will not be divulged to third parties, or used without your permission