Correction of directional errors for radiometric and photometric standard detectors

Changes in beam geometry during the calibration and subsequent testing of o ptical detector standards can cause errors which appear as uncertainties in the responsivities of the detectors. These uncertainties, caused by non-id eal detector input characteristics and changes in input beam geometry, can be decreased significantly if the detector response is always corrected to a reference beam geometry such as a collimated beam normally incident on th e detector surface. An integral directional error can be determined for rad iant power, luminous flux, irradiance and illuminance detectors by calculat ing the weighted integral of the product of the measured source radiance an d the directional error over the solid angle produced by the light source. A conical directional error is introduced, and used to describe the case of circular and uniform radiant sources (e.g. exit port of an integrating sph ere) and circularly symmetric detectors. An evaluation is presented of the conical directional error, a directional response correction factor, the re sults of directional response measurements, and directional response correc tion factors for some practical standard detectors (such as diffuser-input InGaAs and integrating-sphere-input silicon irradiance meters, silicon phot odiodes, and pyroelectric radiant power and irradiance measuring detectors) .