An optical power scale is established at Ulusal Metroloji Enstitü sü (UME) using the helium-cooled primary-level electricalsubstitution cryogenic radiometer. The scale is established at discrete laser wavelengths of vertically polarized tuneable Ar ϩ , fixed He-Ne, and Nd:YAG (with second harmonic) laser sources. To increase measurement accuracy, laser intensities are stabilized to better than 0.009% using an electro-optical modulator. The spatial profiles of polarized laser beams are cleaned with a spatial filter. The optical power is measured using the static substitution method with an uncertainty of a few parts in 10 Ϫ4 . Repeatability of optical power measurements in the static substitution method, the measurement of window transmittance, and the measurement of power in a scattered beam are the most significant uncertainty components.
In order to characterize photometric properties of retroreflectors, a fully automated retroreflector measurement system is designed in National Metrology Institute of Turkey (UME). The system is composed of a lighting projector, a goniometer, filter radiometers, 100dB transimpedance amplifiers, and 24-bit resolution analog-digital converter card with a special software. The established system provides a new calibration capability to determine the luminous intensity and retroreflection coefficients of the retroreflective materials with the expanded uncertainties of 1.07% and 1.13% (k=2), respectively. The traceability in retroreflection measurements was linked to the detector-based photometric scale of UME.
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