Yea, light leak can herm them. In my case, I don't know. I thought it might be the unstable Genetics and fem seeds...so I went with reg seeds but 3 out of four females hermed right away. I'm thinking...I don't flip them to flower correctly. I just go from 20/4 to 12/12. I heard some growers go dark for 48 hours before flip. I don't know, I have been keeping record of all I my observations. I have to say herm plants have produced very potent weed for me.