A light transmission control device (10) used for privacy windows and automobile sun roofs etc is disclosed. The device may be based on electrochromic or polymer dispersed liquid crystal (PDLC) technologies. Unwanted reflections due to refractive index differences at optical interfaces within the device are reduced by the incorporation of an index-matched resin in the gaps between individual light transmission control elements (3) and the transparent cover panels (1,2) enclosing them. This makes the seams between the individual planar control elements less visible, so that the visual quality of the device is improved, irrespective of the number of the light transmission control elements employed in it. Thus a larger number of smaller control elements may be used, which results in a lower manufacturing cost. Each light transmission control element comprises a pair of transparent substrates (31,32) provided with transparent electrodes (33,34) facing each other and in contact with an electrically responsive light control layer (35) whose transmissivity is adjustable by varying the voltage applied across the pair of transparent electrodes. Furthermore, an indexmatching layer (8) is injected into the spaces between two cover panels and the transparent substrates and cured to form a transparent solid layer. In addition, the end faces of the transparent substrates (not facing the cover plates) can be tapered to further reduce unwanted reflections in the direction of the viewer.