In other applications, photometry refers to the technology of measuring radiation quantities that are spectrally weighted with the spectral distribution response of a standardized human eye. Certain colour quantities are also included in SP's work as National Measurement Laboratory. These measurements are often referred to as colorimetry. Radiometry and photometry - Primary standard Many of the radiometric and photometric measurements made at SP are traceable to a cryogenic radiometer, based on substitution by electrical power. Radiant power is absorbed in a cavity, affecting its temperature.
Electrical power is supplied to the cavity to produce an equal heating effect.
By cooling the cavity to a temperature of about 4 K, its thermal characteristics become such that the equivalence between optical and electrical heating is extremely good. The electrical power can be measured very accurately. SP calibrates not only general optical measurement equipment, such as photometers, radiation detectors, radiometers and optical materials, but also special equipment for various applications, such as fibre optics , solar radiation and chemical analysis . Fibre optic telecommunication is an important, dynamically developing area, with major requirements concerning the calibration of power meters, spectral analysis equipment, wavelength meters, optical attenuators and reflectometer equipment. Within the health care sector, there is a growing need for calibration of analysis equipment for optical quantities, e.g. for absorbance and wavelength.