The transmittance of a photochromic (PC) window is reduced in sunlight but returns to its original value in the dark similar to photo-sensitive sun glasses. A 30 cm x 30 cm double glazed window containing a PC multi-layer coating on a single glass pane has been developed. A single PC glass pane can be used to build a window with a low heat transfer coefficient, e.g. double or triple glazed unit, using existing technology. To develop the PC glass with a multi-layered coating that combines chromogenic and photoactive materials we employed sol-gel chemistry approaches and up-scaled the synthesis. Double glazed windows have been assembled using PC glass with two different layer configurations. The transmittance (T-vis) was reduced from 76% to 35% under outdoor solar radiation (750 W/m(2)) within 15 min.