Compared to the basis of equal exposure, in joules per square meter (J/m2) the mutagenic and toxic effects in L5178Y mouse lymphoma cells of radiation emitted by some fluorescent lamps and a sunlamp are quantitatively similar to solar radiation effects at the earth's surface. When the relative intensities of radiation are taken into account, the artificial light sources range from 8 to 1/222 times as mutagenic and 4.1 to less than 1/99 times as toxic as sunlight.