The solar actinic flux has been measured directly and spectrally resolved between 280 nm and 330 nm by means of a spectroradiometer. From these measurements the photolysis frequency J(O1D) of ozone is calculated using ozone absorption cross-sections and O(1D) quantum yields from the literature. Different published wavelength dependencies of the O(1D) quantum yield data are used to compare the spectroradiometric J(O1D) values to J(O1D) data measured simultaneously with a chemical actinometer. This field comparison supports laboratory studies that have measured O(1D) quantum yields of about 0.2 to 0.3 between 315 nm and 320 nm. Implications for tropospheric photochemistry are discussed. ¿ American Geophysical Union 1995