This paper presents the derivation of the simple monthly luminous efficacy models to be applicable in daylight design and practice. Illuminance and irradiance data from the CIE IDMP station in Bratislava and climatological data from the Slovak Hydrometeorological Institute as well as data obtained from the satellite representing the climate of Bratislava are used in this study. Three models of luminous efficacy based on statistical analyses are proposed. New models are compared with the Perez model and results are discussed. Finally the study is devoted to predict exterior illuminance using the proposed luminous efficacy models and derived from satellite irradiance data. The advantage of the presented approach is in application of irradiance data regularly measured on the ground and data from satellite images when no measured illuminance is available. After a simple calculation processing the results have shown good accuracy in terms of the RMSE and MBE when comparing the new model with the Perez model as reference.