Modern systems are more complex than that. My '15 Mazda3 has them, and it's done using a forward-looking camera. The camera looks for oncoming white light, or

Modern systems are more complex than that. My '15 Mazda3 has them, and it's done using a forward-looking camera. The camera looks for oncoming white light, or red light, so it'll keep the high beams on (usually) even when there's reflections from signs, but turn them off for the car driving in front of you, or of course for any oncoming cars. Your photosensor system probably won't dim the lights for cars driving in front of you, as the red tail lights likely aren't bright enough, and now you're irritating the people you're following.