Breakthrough of ultraviolet light from various brands of fluorescent lamps: lethal effects on DNA repair-defective bacteria.

In a comparative study of 17 pairs of 15 W fluorescent lamps intended for use in homes and purchased in local stores, we detect over 10-fold differences in UVB + UVC emissions between various lamps. This breakthrough of ultraviolet (UV) light is in part correlated with ability of lamps to kill DNA repair-defective recA-uvrB- Salmonella. Relative proficiency of lamps in eliciting photoreactivation of UV-induced DNA lesions also plays a prominent role in the relative rates of bacterial inactivation by emissions from different lamps. Lamps made in Chile, such as Philips brand lamps and one type of General Electric lamp, produce far less UVB + UVC and fail to kill recA-uvrB- bacteria. In contrast, all tested lamps manufactured in the USA, Hungary, and Japan exhibit readily observed deleterious biological effects. When an E. coli recA-uvrB-phr- (photolyase-negative) triple mutant is used for assay, lethal radiations are detected from all lamps, and single-hit exponential inactivation rates rather closely correlate to amount of directly measured UVB + UVC output of each pair of lamps. Although all lamps tested may meet international and United States standards for radiation safety, optimal practices in lamp manufacture are clearly capable of decreasing human exposure to indoor UV light.