I'm not sure how much light it would block and I.m not going to spend $20 to find out. I read in here that they don't recommend it on car headlights but I wonder if that is due to light blockage or the coating altering the beam pattern. I am a bit supprised that there CS also claims that this coating isn't UV resistant. That makes little to no sense. If you have a coating that is designed to make things "waterproof", doesn't that also indicate that in most instances it is going to be outside. And if it's outside, doesn't that also indicate that it will be exposed to sunlight as well. This seems like a rather large expense for what would be a rather short lived protection.