When developing restoration decisions for conservation of historic houses, determination of daylight performance of the spaces is important for new usage proposals. Among the rooms located around sofa in Anatolian historical houses, main room is the most spectacular space. It should have sufficient and homogeneously distributed daylight in restored houses. This study aims to examine daylight performance of main room and preserve original lighting features in restoration and re-functioning decisions. For this purpose, Kaçıklar, Zabunlar, Kestaneciler and Zühtü Bey Houses, were selected as examples for the research. Daylight performance measurements were taken in main rooms in all seasons, in the morning, at noon, in late afternoon using an illuminance meter. As a result of the study, it was determined that illumination was not sufficient for all seasons in unrestored Kaçıklar House, sufficient for all seasons in unrestored Zabunlar House, in restored Kestaneciler House, also sufficient in restored Zühtü Bey House in autumn whereas insufficient in other seasons. In Kaçıklar House, opening the window that was closed, cleaning the paint on top windows, selecting a light-coloured wall finish material will positively affect lighting values. In restored Zühtü Bey House, the window, converted into a built-in cupboard, and the closed top window to be restored to original state and cleaning of improper paint on the top windows on the south wall will affect the lighting level positively. This study is important in terms of determining specific daylight illumination properties of historical houses and underlines the improvement of repair and conservation decisions.