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Using a new, high-temperature black-body radiator developed by the All-Russian Institute for Optophysical Measurements (VNIIOFI), Moscow, and applying newly developed methods and equipment, the black-body-based spectral irradiance scale of the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, has been extended and its uncertainties have been reduced compared with previous results. The pyrolytic-graphite Planckian radiator BB3200pg, which can be operated at temperatures up to over 3300 K, is presented and characterized along with modifications to optimize uniformity and stability. The determination of the radiometric black-body temperatures is already well established by measuring the weighted irradiance using filter detectors without imaging systems. This method is compared and verified with results based on self-consistent spectral irradiance measurements using fast-scanning spectroradiometers. In addition, a laser-based method for the determination of the radiometric temperature is presented and compared with conventional procedures of radiationtemperature measurement. The implementation of this additional method into the radiometric chain of the PTB is illustrated. Improvements in the uncertainty budget of the spectral irradiance scale are discussed.

Based on extensive investigations of almost 100 high-power quartz-halogen lamps covering thirteen different types, seven different manufacturers and different batches with a total operating time of about 27000 h, a new type of lamp (1000 W T6 modified FEL-type lamp, Osram Sylvania Inc.) has been selected and its operating conditions have been optimized. This lamp, which after seasoning is about ten times more stable than the best lamps used before, is recommended as a reference and transfer standard of spectral irradiance in the whole range between 250 nm and 3 µm. While excellent short-term and long-term stability over operating times of several hundreds of hours can be achieved, the disadvantages of the new standard lamp lie in a long seasoning time (80 h to 100 h) and a noticeable sensitivity of the seasoned lamps to shock and vibrations. Typical results of the characterization, calibration and reproducibility of the new standard lamp are presented and discussed in order to illustrate its performance and to demonstrate how to use it under optimal operation conditions.