Maybe quite soon, eyeglasses will have tiny batteries, microchips and assorted electronics to turn reading power on when you need it and off when you don’t. Traditionally, people who hit their 40s often need extra optical help as farsightedness sets in. They may buy bifocals or no-line progressive lenses. But such glasses have a drawback: the lenses that magnify fine print also blur objects more than an arm’s length away when a wearer looks down, distorting the view when on a staircase, for example, or when swinging at a golf ball. New electronic spectacles, made by PixelOptics and called emPower, are intended to handle that problem with an unusual insert in the bottom part of the lenses: liquid crystals, cousins to the familiar ones in television displays. The crystals change how the lenses refract or bend light, just as varying levels of thickness do in traditional glasses. Only one downside: You have to charge them overnight.