Previously reported thresholds for UV-B dose and dose-rate were determined under artificial light regimes using more than an order of magnitude less visible light than round naturally. Near-UV and/or visible light is needed for photoreactivation and the accuracy of earlier findings may have been influenced by less than maximum photorepair in the laboratory. Experiments with shrimp larvae and adult euphausiids, comparing survival at various UV-B doses and dose-rates combined with different levels of near-UV and visible irradiance, suggest that photorepair reaches maximum levels at relatively low visible light intensities. Adult euphausiids successfully avoided moderate UV-B combined with visible light, but were attracted to and ultimately killed by higher levels of UV-B irradiance would become an important factor in a new solar spectral distribution caused by ozone depletion.