In the last few years rear lamps have assumed both a functional and aesthetic role: the safety factor of a car, and the style that defines the brand and the model of a car. The complex shapes, the weight and volume reduction and the worldwide vehicles export lead to critical temperature and humidity rear lamp working conditions. The effects of condensation on the perception of car quality have a negative impact on the potential buyer or car owner; moreover, condensation has negative effects on electric and electronic components – mainly the LEDs – causing sometimes problems like delamination and the siliconic lens detachment. It is hence of fundamental importance to be able to predict these phenomena in an accurate and reliable way. This study aims to replace the currently in use CFD Fogging/Defogging simulation approach with a more accurate one taking advantage of Multicomponent Gas and Liquid Film models. The solver used is STAR-CCM+ by CD-adapco. The study will follow this line: analysis of the physics of the phenomena and of the software models, application to a simple real case and its experimental verification (in order to apply the new methodology to an industrial case such an Olsa series production rear lamp), conclusions and future possible development.