I would think that you would count the days with light spotting because it is still menstrual blood--just less of it.
Here is a link you may find helpful in calculating your ovualtion:
You can copy and paste into your address line.
Another way to tell when you are ovulating which I have mentioned in several of my posts is to check your vaginal discharge.
When it becomes clear and sticky (like egg whites), you will ovulate within the next 24 hrs.