I have 20% all around on my car, which is black by the way and also is illegal in my state. I based it on looks and ability to see while driving at night. I have no problems what so ever seeing at night and it looks darker than it really is because of my dark interior. Should look great on a white car with no visibility issues at night. I know some people go darker but I used to have double limo tint on an older car of mine and would have to roll down my drivers window to see curbs when making left turns at night