National Physical Laboratory

Spectral Radiance and Irradiance Primary Standard

The facility is used to calibrate both radiance and irradiance sources such as integrating spheres, strip lamps, and FEL and Polaron irradiance lamps. Its ultra high black body can be used for space and air borne remote sensing instrumentation.

SRIPS Facility Layout
Schematic layout of SRIPS

NPL's Spectral radiance and irradiance primary scales are directly linked to NPL's cryogenic radiometer through the use of calibrated filter radiometers. The filter radiometers (FR) are used to determine the temperature of a state-of-the-art high temperature black body (UHTBB), which is then used as a primary standard source whose spectral radiance can be determined from Planck's black body equation. The spectral radiance and irradiance scales are transferred to transfer standard sources using the SRIPS facility, as below. This facility is not limited to the calibration of special source lamps, but can be adapted for fast scans of customer lamps.

The light source being calibrated is measured relative to the UHTBB. Given the temperature of the black body, the radiance of the black body is known at any wavelength.

A filter radiometer measures a specific spectral band from a broad band electromagnetic source. The basic components of any FR are a light detector such as a photodiode, an optical filter for example coloured glass and an aperture. The filter radiometers have been previously calibrated. All measurement instrumentation is mounted on a fully automated, computer controlled stage.

The facility can calibrate, at any one time, up to four lamps that are held at constant current under or up to six lamps with their own power supplies. Lamps are usually calibrated directly against the UHTBB but can be calibrated against another standard lamp or source, if required.


The spectral radiance and irradiance primary scales facility is a dual-purpose system. All modes are fully automated and the system is supplied with the appropriate software and support electronics. A comprehensive manual compliments the system.

Operating Details

250 to 2500


Integrating spheres, strip lamps, and FEL and Polaron irradiance lamps

Black body temperature

Up to 3500K

Black body details

Made of pyroelectric graphite to achieve the best uniformity with reasonable emissivity, argon purged


PMT, Silicon, InGaAs and InSb

Filter radiometers

Calibrated on NPL's filter radiometer calibration facility


Double monochromator, chopper for infrared measurements, UV filter wheels, integrating spheres alignment aids

NPL calibrated filter radiometers
Filter radiometer calibration facility

NPL's support includes the installation of the facility and training in its use.

Contact us for further information

Call the Instruments team on: 020 8943 6539

Last Updated: 10 Apr 2017
Created: 31 Jul 2007


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