I grow naturally dark brown (almost black) hair. Applying this once a week for 5+ hours makes my hair light brown/dark blonde with carmelish tones.
This is review for plain old Cinnamon to lighten dark hair at home. Cinnamon has very low amounts of peroxide lightening properties. My friend had saw some beauty gurus online lighten their hair with a mixture of thick hair conditioner, honey and cinnamon powder from kitchen pantry. You have to use it 2-3 times to get any change in shade. 8-12 times to get to a light auburn tone and leave it on for 12 hours each application.
So we gave it a go ourselves---without the honey and added olive oil. Don't think olive or honey have any affect on color but will help condition your hair throughout the process. Both of us have virgin hair, never been colored. She has black hair and I have regular dark brown hair. The porportions we used are for 1 application on medium length hair. 4 tablespoons Cinnamon powder, 1 tablespoon of olive oil, 1/2 cup of thick conditioner, wrap with shower cap. I left it on for 4 hours and she left it on for 12 hours. Rinse and shampooed right away as cinnamon can be irritating on skin. My hair had very subtle auburn tint, almost 1/2 shade lighter. Hers went a shade lighter. She did another application a couple of week later and now she has gone to an auburn color.
I wouldn't do this unless you really want a natural alternative and also dark hair. Another plus is the nice powdery cinnamon scent you get after you wash your hair.