Electrochromic (EC) windows enable to change their optical transmittance by applying appropriate electrical signals to the window structure. In many applications; such as "smart" EC buildings' windows is required, an automatic control of the window's transmittance, in order to assure a constant level of transmitted daylight for different outdoors' illuminations. For this purpose we develop an analogue three-state electronic regulator which controls an "all sol-gel" EC device intensity of transmitted light on a constant pre-selected level. In this paper, first of all, the structure and the performances of an all sol-gel EC window is given. Then the electrical schematic of the regulator is represented and explained in detail. The performances of the regulator are demonstrated by electrical and optical measurements. At the end a demonstrational application-EC sun-glasses with an accompanying handy regulator-is presented. (C) 2002 Elsevier Science B.V. All rights reserved.