An active, transparency-controlled window comprises at least one layer of a material that is transparent to at least selected wavelengths of light; at least one layer of photochromic material having a transparency, to the at least selected wavelengths of light, that can be controllably altered by an activating light; and a controllable source of light that activates the photochromic material to controllably alter the transparency of the photochromic material to the at least selected wavelengths of light. The material that is transparent to at least selected wavelengths of light may be a material selected from the group consisting of glass and plastic.