We consider path protection in the routing and wavelength assignment (RWA) problem for impairment constrained WDM optical networks. The proposed multicost RWA algorithms select the primary and the backup lightpaths by accounting for physical layer impairments. The backup lightpath may either be activated (1+1 protection) or it may be reserved and not activated, with activation taking place when/if needed (1:1 protection). In case of 1:1 protection the period of time where the quality of its transmission (QoT) is valid, despite the possible establishment of future connections, should be preserved, so as to be used in case the primary lightpath fails. We show that, by using the multicost approach for solving the RWA with protection problem, great benefits can be achieved both in terms of the connection blocking rate and in terms of the validity period of the backup lightpath. Moreover the multicost approach, by providing a set of candidate lightpaths for each source destination pair, instead of a single one, offers ease and flexibility in selecting the primary and the backup lightpaths.