How can I produce feminized seeds?

I want to know how to make feminized seeds but I have done some research and have came to a bit of a brick wall, do I need a hermie or do I need a female plant ? and force a female plant with some spray which I can't remember what is called now and spray of female buds?

Please help if you know how to make feminized seeds

From what I've "heard" hermies produce 99.9% female seeds.
If you stress the plant it will likely hermie.
Light stress seems to be the safest to me.
Changing the light schedule while in flower will likely work.