Mercury arc lamps (the kind used in football stadiums) are not much better, since they emit a lot of ultraviolet light, which contributes to astronomers' woes without illuminating the action in a way that the human eye can detect.

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But too much mercury can be toxic, and mercury-based lamps can take an hour to disinfect a room.

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This system can run for up to 25, 000 hours without replacement, roughly five times longer than mercury-based lamps.

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Proponents argue that CFL lamps contain only very small amounts of mercury.

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Mixes the mercury and rare earths that make metal halide and CFL lamps work.

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