Methods of measuring changes in paper structure due to visible light ageing are discussed in this poster. During exhibition, historical paper documents can deteriorate due to their exposure to both ultraviolet and visible radiation. They can also become damaged after exhibition, during dark storage in a depository, due to post-irradiation effects. Light damage to paper documents is usually very extensive; unfortunately it is most often irreparable and irreversible. Many characteristics of paper need to be studied to obtain complex information about the mechanisms of paper degradation due to light. Conditions of artificial ageing and measurement methods for optical properties (UV-VIS spectroscopy, coordinates of colour space CIELAB, K/S), chemical properties (EPR spectroscopy, pH value of cold water extract, FTIR spectroscopy) and mechanical properties (breaking load, ductility, folding endurance) are described. Finally, post-irradiation effects (PRE), which occur during storage in the dark, are examined. Preventive conservation, through the use of UV and visible filters, and control of photometric values of light sources are very important.