@terrimclaughlin I love my cactus! This particular one is very old. I believe it likes to be root bound. I live at the 50th parallel north and we are getting about 8 hours of daylight and 16 hours of darkness. I believe that is one of the tricks to getting it to flower.
@Ru8y, I have mine in a sunny window all the time. The only darkness it gets is in the fall and winter, when Winnipeg gets its regular hours of fading sunlight. It is always very picky with watering while it flowers. I often lose many buds when I give it too much water.