The subject of the research is the quality, ageing and degradation of glass, which is used in the construction of window openings of buildings in relation to its light transmission and influence on the light environment. The article evaluates the influence of ageing of glass structures over the years on the light environment inside permanently occupied buildings. By default, laboratory measurements and calculations are used to determine the value of glazing transmission when it is possible to set and ensure marginal conditions. Furthermore, computer simulations were used to demonstrate the state of daylight in declared spaces in relation to the values of light transmission and the life cycle length of the glass element.