Number 293 (Story #3), October 30, 1996 by Phillip F. Schewe and Ben Stein A PHOTOELECTROCHROMIC (PEC) cell harnesses a photochromic layer, which changes color by absorbing light, with an electrochromic layer, which changes color under the influence of an electric field, to make a self-powered smart window. On a sunny day the one layer supplies the photovoltage needed by the other layer to darken the window, letting in less light and thus lowering air- conditioning costs. This photoelectrochromic process, developed by scientists at the National Renewable Energy Lab in Golden, Colorado, might also be useful in display applications. (C. Bechinger et al., Nature, 17 October 1996.)