Comparison measurements on regular spectral transmittance

A comparison of the scales of regular spectral transmittance of the Helsinki University of Technology (HUT) and the Swedish National Testing and Research Institute (SP) was made using a set of 3 absorption neutral-density glass filters and a flat piece of UV grade synthetic silica. The nominal transmittance of the samples were 0.01, 0.1, 0.5, and 0.93. The spatial transmittance profile and the temperature coefficient of spectral transmittance of the filters were measured. A good agreement was found between the results of SP and HUT, since most of the differences in transmittance values are within the relative standard uncertainty of the comparison ranging from 0.2-2% (level of confidence 68%). (C) 1996 John Wiley & Sons, Inc.