Tribology has a major role to play to reduce the total energy consumption worldwide. Yet, the lubricant behavior in extreme conditions is poorly known, and therefore unpredictable. In this project, we propose to couple a Brillouin Light Scattering set up with a tribometer to carry in situ spectroscopy characterization of lubricants in a highly confined contact. This experimental approach will lead to simultaneously measure the thermodynamic state of the lubricant, its structural dynamics and the resulting macroscopic friction causing high energy dissipation. It will shed light on the mechanisms driving the lubricant response. Collected data will enable to go further on two other challenges already raised by many industries i) the evidence of the passage of additives in a contact and ii) the amount of additives adsorbed on the contact walls. The next step will be to implement the technology developed at laboratory scale in on-line characterization devices intended for business use.