Photometry and Radiometry - Research Projects
 Monochromator-Based Cryogenic Radiometer Facility
Measurement of Colour Discrimination Thresholds
This facility is used for the first level calibration of transfer standards of absolute spectral responsivity. These transfer standards are the basis for the realization of several photometric and radiometric standards. Most NMI's now have cryogenic radiometer facilities, but NRC was the first NMI to use monochromator-based rather than laser based apparatus. The advantage of the monochromator approach is that it allows fully automated measurements over a wide spectral range, and the cost of setting up and maintaining the facility is much lower than with laser-based apparatus. The cryogenic radiometer operates at liquid helium temperatures and has an overall accuracy of 0.02%. Over the last few years, the cryogenic radiometer facility has been used at NRC to realize new spectral responsivity scales in the near-IR ( 900nm - 1600nm ) and in the UV-VIS ( 300nm-1000nm ) This work was motivated by current international comparisons of spectral responsivity scales in those spectral ranges, and by the need to improve the accuracy of our spectral responsivity calibration services. Current work involves the realization of a spectral responsivity scale in the UV ( 200nm - 400nm ) using as transfer standards PtSi and Si detectors. This work is being carried out in preparation for an international comparison being piloted by PTB.
For further information, contact L.P. Boivin.
Over the last three decades there have been many attempts to produce a formula that could reliably predict the perceived size of small colour differences. The formulas that have been proposed so far are not fully satisfactory and need improvement, which requires that colour discrimination of human subjects be measured and sampled across the full colour space. Joining that effort, a computer-based colour comparison system has been developed that allows any two colours to be accurately set according to their colour coordinates and to be judged relative to each other. The system comprises a PC, a high performance colour CRT and a communication link with a reference spectroradiometer, all of which are housed in a dedicated viewing room. The system has served recently to measure hue dependent effects in CIELAB colour space to be used for corrections in the CIE94 colour-difference formula.
For further information, contact R. Baribeau.
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