In hair coloring cream, what's the difference between 9% and 12% oxidizing solution?

what should i use if i want to go lighter?In hair coloring cream, what's the difference between 9% and 12% oxidizing solution?
The 12% is stronger. If the hair is already colored you can not go lighter using another color. ( With any type of solution.) You would have to use a bleach to do that. You can highlight through the base color to give a softer, lighter look.