The power consumption issue in the wired optical networks has become a major challenge, due to its considerable economic impact and potential adverse in°uence on the envi- ronment. Based on many researches and analytic studies the global internet tra±c will continue to increase annually, on the grounds of continuous improvement of bandwidth-intensive applica- tions like transmission of high quality multimedia and capacious data exchange opportunities, which stipulates the requirement of increased information transmission speed at all system layers. In the Wavelength Division Multiplexing (WDM) systems, transmission speed can be enchased by reduction of channel spacing or increment of channel transmission speed. However, owing to interference between operating channels, reduction of sub-band spacing can adversely a®ect system's transmission reach, by increased number of signal regeneration procedures, which deter- mines the higher power consumption values. In addition, due to the limitations in the spectral band appropriate for data transmission, an available spectral band di®ers from one network to another, based on the initial requirements for particular system, which can be ful¯lled by dif- ferent network designs with di®erent power consumption values. Therefore the tradeo® between spectral e±ciency and required energy consumption should be evaluated. In this work authors compare the Single-Line-Rate (SLR) WDM systems with di®erent available spectral band, which operates on the most commonly used transmission signals, in order to demonstrate relation between the enchased spectral e±ciency and its impact on the relevant systems power consumption by means of power e±ciency and 3Rs' (reampli¯cation, retiming, reshaping) power ratio evaluation. The results are presented as functions cross-channel intervals and data transmission speed for systems that utilizes entire C-Band (4.4 THz) and systems with limited spectral band.