There are several methods used in lighting design. The realistic methods have been developed by the computer graphics which use the engineering computational tools and architectural rendering together. Although lighting designers would design an accurate lighting system which provides desired illuminance levels through computer graphics, it is still necessary to propose optimal and alternative solutions by maximizing comfort conditions and minimizing energy consumption by practical techniques. Thus, the purpose of this study is to propose an optimization model for offices to estimate the accurate layout, number and type of light sources according to visual comfort conditions and energy efficiency. Model is conducted mathematically based on the primary objective which is to provide uniform illumination on work plane with the constraints about vertical illuminances and luminance values. Model named OptimLUM is validated by comparing measurements and simulations. Finally, OptimLUM offer some energy efficient layouts for different office sizes with different number and type of light sources. To be more energy efficient and decrease the energy loads by artificial lighting, these layouts were integrated with daylight. Unlike common lighting design solutions, OptimLUM offers unsymmeterical but more energy efficient layouts by using minimum number of luminaires. According to outputs of the model integrated with daylight, for artificial lighting design in offices, lighting designers should decide on the number and type of luminaires by comparing the darkest and day usage conditions. As a result, by using OptimLUM during the design phase, designers can provide visual comfort conditions for office users while reducing the energy loads of artificial lighting.