Why should we apply optical simulation and light modeling software? More and more improperly designed low-grade products can be found on the market, which can cause negative experiences and financial losses both to the vendors and to the users. Incorrect prototypes or products always require re-design. The worse option is the re-manufacturing, which is extremely expensive. To avoid these problems, we can apply software for optical design and analysis, which is an economical solution. The prototype of the product will be properly designed, thus posterior modification or remanufacturing of the molding and forming tool is avoidable. The time of the design can be significantly reduced as well. A professional light-modeling and simulation software called OPTIS SPEOS is used at the BUTE - MOEI, to design and develop different optical and lighting systems. This paper describes some of our experiences with optical design and light modeling.