This read-only CoriantTypesOpticalPower value is the equivalent signal-degrade optical power threshold, defaulting to -18.0, applied to the protection port rather than the working port. It matters because it governs whether the OPS group would consider switching back to the working path or reporting the protection leg itself as degraded. For example, if the protection port's received power falls below -18.0 dBm while traffic is running on it, the group would flag the backup path itself as degraded, an important warning that redundancy has been weakened.