In order to evaluate the benefits of such on/off strategies, in this study we first propose an accurate model of power consumption and housing constraints of both IP and WDM layers of an IP-over-WDM translucent optical network architecture. Second, we present a Traffic-Aware design technique (i.e., network design allowing reconfiguration when traffic varies) as a Mixed Integer Linear Programming (MILP) formulation based on an extended version of the so-called 鈥渃onnectivity graph鈥? Third, we evaluate the impact on power consumption of Multi-Layer network architectures when coherent and non-coherent transmission technologies are employed. Fourth, we analyze the energy savings arising from switching on/off devices jointly at IP and WDM layers when traffic demand changes. We show that the contribution of the WDM layer to the power consumption is about 10%of the overall network consumption regardless the employed transmission technology and the type of traffic. We demonstrate that in Multi-Layer networks and for current traffic needs, coherent transmissions do not exploit their extended reach and they show the worst performance in terms of energy consumption although they represent a future-proof technique to cope with the expected increase of traffic over long distances. Finally, we present our Traffic-Aware design results on Multi-Layer translucent networks showing that we can save on average up to almost 50%of the peak-traffic power consumption.