Ovulation test strips show two red bars, or one dark and one light bar, after the follicle is expelled. Ovulation test strips, on the other hand, are used to predict whether ovulation has occurred by detecting peak levels of luteinizing hormone (LH). It is simply an aid for women to determine if they are ovulating. Ovulation usually occurs 24-48 hours after a positive test. 1. Two red bars: Ovulation is about fourteen days before menstruation. When the follicle matures, it will be two red bars, whether ovulated or not. 2. One dark and one light: when it is about forty-eight hours after ovulation, the ovulation test paper will slowly turn into one dark and one light, gradually becoming negative.