Question about OPK

Stephanie • Mother to a sweet baby girl born 14 October 2015 💗👑💗

Ok, so apparently I am in my fertile window according to Glow (last AF was 9/22 and next expected is 10/19). The top photo was taken 10/1, middle this morning and bottom this evening. I know they're all negative, but how is it that my test line is getting lighter?? I thought it would be getting darker as I got closer to ovulation?? Please help!! I'm new to these tests!! Thanks in advance. :-)