The exploration of the sales market of furniture and other domestic goods both from solid wood and veneer shows that consumers currently prefer articles from wood with a definite brightness, i.e. lighter hues. This factor is of great importance for veneer production as well as the manufacture of wood boards, with their subsequent veneering. To investigate the possibilities to increase brightness, it is of interest to study the optical properties (mainly reflection capacity L*) of wood in the visible range of the electromagnetic spectrum, depending on the regimes of its hydrothermal treatment, i.e. water temperature and steam treatment time. It has been shown that hydrothermal treatment influences the brightness of Silver birch (Betula pendula Roth.).