I just thought I should inform most people in here, because they keep asking about red light district in Amsterdam. So, there are more then one red light area in Amsterdam. The main red light area is called De Wallen, then ther are Singel and Pijp.
You can read more from http://www.wikisexguide.com/wiki/Amsterdam#Amsterdam_Red_Light_Districts
Yes, when I stayed at a hotel on the Singel canal, I was surprised by the number of prostitutes in the windows of that neighborhood. However, it did not make the area uncomfortable for an adult.
We did stay at the De Wallen Red Light District. My wife felt scared first day, but next day she was fine and understood that se workers will not bother you.