Rear Sun Sensor - Auto Headlights

I recall when daytime running lamps (drl) were first introduced the compelling example used was that of a car coming around a curve on a mountain road with the sun beaming from behind.  The oncoming cars had a hard time seeing the car on the curve because of the strong sun glare coming from  behind.  However, when the car on the curve put the headlights on it became easily visible.  Today, some vehicles have drl's but not all.  My idea is to equip all vehicles with a rear sun sensor that would detect intense sunlight (like when the sun is setting in the evening at that low angle).  When the intense sunlight is detected the headlights will automatically turn on.  This would make cars with intense sunlight shining from behind more visible to oncoming vehicles thereby increasing safety.  Many autos already have headlights that turn on automatically when the outside light dims beyond a certain point.  Therefore, to implement this highly effective safety measure should be relatively simple.