I've heard that lemon makes your skin lighter, but not everyone can tolerate lemon on the skin. More serious skin lighteners - I think they're mostly chemicals. It's similar to hair bleaching, that damages your hair.
I've been using PSF PhytoNutriv Lightening Serum and getting good results. It's slow, but gentle on the skin also. The website shows the ingredients. I don't think this is an "organic" product, but it's definitely one of the lighteners with more "natural" ingredients.