Hi. I know there's lots of questions like this in the site I just haven't find the exact thing I'm looking for. My hair is naturally black and I want to go to a medium or light brown without bleaching or dye. I tried a brown color with 20 developer and it didn't change much. It got a little reddish but not lighter.
Please help me and give me as much ideas as you can, I would really appreciated it

Without using some bleaching compounds, it would be impossible to change black to light brown.

Black hair is tricky and has a tendency to turn red, so I would consult with a beautician who has a lot of color experience.