Several CIE Technical Committees discussed the advantages and disadvantages of different spectral interpolation methods during the past years. Linear, Lagrange, cubic spline, and Sprague methods were under discussion. We have investigated the colorimetric differences caused by using the different interpolation methods, and showed that Lagrange, cubic spline, and Sprague methods provide very similar results for most well-behaved spectra. As a further result, we found that the 5-nm sampling and using the 5 nm tables of the CIE Technical Report "Colorimetry" is almost as good as an interpolation to 1-mn sampling and colorimetric calculation using the 1-mn tables of the CIE colorimetric standards. (c) 2005 Wiley Periodicals, Inc.