Newborns really do not have a frame of reference for fear of the dark yet - they don't know what scary is since they have never seen frightening movies, etc. It is more likely that her sleeping pattern has adjusted for better daytime sleep. Try to keep her up more during the day and she will be tired enough to sleep during night time hours. When it is time to put her down for the night, feed her then give her a warm bath; turn down the lights and rock her, cuddle until she begins to drift off. Put her into her crib, then gently rub her arm, back, etc. until she is sleeping. If you make it a routine, she will be able to adjust her sleep pattern to night hours. Depending on her age, however, she will still need night time feeding, just repeat the routine (less the bath) and let her get used to it.
at 4:28 PM on Feb. 25, 2010