The aim of the article is to evaluate the criteria and boundary conditions of measurement of light transmission of windows and glazed structures of buildings. The article deals with possible measurement variants and the influence of external boundary conditions on the resulting values of light transmission of windows and glazed structures. Ensuring the correct criteria and boundary conditions of measurement is the basis for ensuring the correct results of the measured values of light transmission. Light transmission defines parameters of glazing of windows and glazed structures of buildings in the area of evaluation of daylight, which is a basic hygiene requirement in rooms with residents. Based on these requirements, a minimum window size is proposed when designing buildings with a connection to the interior and its use. The size of windows influences the architecture design and energy performance of buildings and thus the environmental burden during construction and operation of buildings.