By 1900, one of Thomas Edison’s carbon filament bulbs would provide you with ten days of bright, continuous illumination, a hundred times as bright as a candle, for the money you’d earn with our sixty-hour week of hard labor. By 1920, that same week of labor would pay for more than five months of continuous light from tungsten filament bulbs; by 1990, it was ten years. A couple of years after that, thanks to compact fluorescent bulbs, it was more than five times longer. The labor that had once produced the equivalent of fifty-four minutes of quality light now produced fifty-two years. And
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