The measurements involved in the realization of a spectral irradiance scale in the near IR are described. Interference filters were used in conjunction with absolute radiometers to calibrate two different types of tungsten-halogen lamp at nine discrete wavelengths in the spectral range of 700-1600 nm. We discuss various aspects of these measurements: the apparatus used and alignment procedures, aging of the lamps and verification of their spectral characteristics, filter properties and measurements, some of the problems associated with the radiometric measurements, and data analysis. In particular it is shown that the interpolation formulas used to obtain spectral irradiance values at other wavelengths must be carefully chosen to avoid spurious errors. Two independent realizations were made; a comparison of the results obtained in the two cases indicated that some of the lamps had anomalous behavior. Finally it is shown that the new scale is in agreement with the scales realized by several other national laboratories within estimated uncertainties.
The paper describes the realization of a new scale of luminous intensity at the National Research Council of Canada, based on the 1979 redefinition of the candela. Two different methods were used. In the first method, the lamps were calibrated directly by means of absolute radiometers equipped with V(λ)-correcting filters. In the second method, secondary radiometers incorporating silicon photodiodes were first calibrated spectrally by means of absolute radiometers, then used in conjunction with V(λ) filters to calibrate the lamps. The sources of error and measurement results for the two methods are analyzed in detail. A comparison of the new scale with the previous platinum-blackbody-based scale indicates that the new NRC candela is 1.2% smaller on average than the old NRC candela.
The use of high-temperature blackbody (HTBB) radiators to realize primary spectral irradiance scales requires that the operating temperature of the HTBB be accurately determined. We have developed five filter radiometers (FRs) to measure the temperature of the National Research Council of Canada's HTBB. The FRs are designed to minimize sensitivity to ambient temperature fluctuations. They incorporate air-spaced colored glass filters and a Si photodiode detector that are housed in a cell whose temperature is controlled to AE0.1 C by means of annular thermoelectric elements at the front and rear of the cell. These wideband filter radiometers operate in four different wavelength bands. The spectral responsivity measurements were performed in an underfill geometry for a power-mode calibration that is traceable to NRC's cryogenic radiometer. The spectral temperature sensitivity of each of these FRs has been measured. The apertures for these FRs were cold-formed by swaging machine-cut apertures onto precision dowel pins. A description of the filter radiometer design, fabrication and testing, together with a detailed uncertainty analysis, is presented. We derive the equations that relate the spectral irradiance measured by the FRs to the spectral radiance and temperature of the HTBB, and deal specifically with the change of index of refraction over the path of the radiation from the interior of the HTBB to the FRs. We believe these equations are more accurate than recently published derivations. Our measurements of the operating temperature of our HTBB working at temperatures near 2500 K, 2700 K and 2900 K, together with measurements using a pyrometer, show agreement between the five filter radiometers and with the pyrometer to within the estimated uncertainties.
A new spectral irradiance scale in the near-infrared was realized at the NRC in 1989-1990. Electrical-substitution absolute radiometers were used in conjunction with interference filters to calibrate FEL and NPL/GEC tungsten halogen lamps in the spectral range 700 nm to 1 600 nm. This paper briefly reviews the method used and presents a detailed analysis of the theoretical and measurement uncertainties involved. Results of the measurements are also discussed briefly.
In 1997, the Consultative Committee for Photometry and Radiometry (CCPR) initiated a supplementary comparison of spectral radiance in the wavelength range from 220 nm to 2500 nm (CCPR-S1) using tungsten strip-filament lamps as transfer standards. Five national metrology institutes (NMIs) took part in the comparison: BNM/INM (France), NIST (USA), NRC (Canada), PTB (Germany) and VNIIOFI (Russia), with VNIIOFI as the pilot laboratory. Each NMI provided the transfer lamps that were used to transfer their measurements to the pilot laboratory. The intercomparison sequence began with the participant measurements, then the pilot measurements, followed by a second set of measurements by the participant laboratory. The measurements were carried out from 1998 to 2002, with the final report completed in 2008. This paper presents the descriptions of measurement facilities and uncertainties of the participants, as well as the comparison results that were analysed in accordance with the Guidelines for CCPR Comparisons Report Preparation, and a re-evaluation of the results taking into account the instability of some of the transfer lamps. Excluding a few wavelengths, all participants agree with each other within ±1.5%. The disagreement decreases to approximately ±1.0% when the anomalous data are excluded from the analysis.
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