how fast does lemon juice work on lightening skin?

Not very effective. It takes months if it works. Also it has some bad side effects of making your skin very dry and sensitive to sunlight.

Best advice is to consult a dermatologist (specialist) or at least ask your primary care doctor.

Here's information on using (freshly msqueezed, pure) lemon juice to lighten skin:

http://www.wikihow.com/Use-a-Lemon-to-Lighten-Your-Skin

Id use some meringue with that limon

There was a much beloved teacher at my middle-school who had a TON of freckles. I remember how we were all so astounded when she showed up at the beginning of 8th grade completely freckle-free. She got so many comments and questions, she finally shared her recipe by writing it on the blackboard. All I can remember is it included lemon juice and oatmeal...no meringue LOL.

Is her name Jan?

Lemon juice has been used for long time to help lighten skin. But as far my experience is concern lemon juice works to a certain degree but it really ends up drying out your skin. I would suggest to use vitamin c serum (or a lightening serum) which has been specially formulated to use on the skin. My sis have used in it on her face for several months and have noticed a big difference on spots and pigmentation.

not very effective.