Measurement and comparison of the ratio, of the direct beam to normal hemispherical solar spectra, in various parts of the world

We study the universality of some recent observations concerning clear-day direct beam solar spectra, of possible relevance to a future standard for CPV testing. Ratios of direct beam to normal hemispherical solar spectra were measured at 12 sites around the world, and the first results of their comparisons are discussed here.