How long can a plant go without sunlight?

I have an Umbrella plant that has gone almost a full month without sunlight and it's still very healthy. Now I know that eventually this plant will die, but the question I have is how long can the plant go without any sunlight? I'm not going to wait around to find out because the plant actually has a lot of personal value to me, but I think it would bean interesting thing to find out. Come to think about it, many years ago when I was in grade school, I did a science experiment testing this. Actually, the test consisted of filtering out different colors from the color spectrum. I believe I had used spider plants. Each plant was kept in a bottle and wrapped with colored film. I remember using red, green, and yellow. Also, one plant didn't have any filters and another was allowed zero light. It would be nice if I could find the data of my childhood experiment, but that information has long disappeared. Perhaps though, that would be a great science experiment for one of my kids.