Since our major concern on the stratospheric ozone depletion is possible adverse effects on the biosphere, it is important to establish the way to determine biologically effective doses of solar UV radiation. The "spore dosimetry" system measuring the lethality of dry bacterial spores on membrane filters has been developed to meet this purpose. The methodology to evaluate experimental correlation with spectral measurements based on the effectiveness calculation has been applied in several field comparisons carried out at Nea Michaniona (Greece), Brussels (Belgium), and São Martinho (Brazil). When plotted against UVB irradiance (total energy below 320 nm), the calculated values of MED (minimal erythema dose), SID (spore inactivation dose) and DND (DNA damage dose) exhibited increasing exponents in power regressions, while the exponents from spore dosimetry exceeded those of the calculated values. The results of calculated versus observed values of SID indicate a general convergence at low to modest dose rates, but at high dose rates the calculated ones tended to yield lower values than those obtained from direct biological measurements.