Hi Scotty, I really enjoy your videos on you tube! Definitely helpful and informative, and love your angle of mechanic humor!
I drive a 2013 Chevy Impala and one thing I noticed is the plastic material(s) used for the rear lights appears to be in pristine condition since the day the car was rolled off the assembly line. The headlight plastic on the other hand...well, it seems to have gone by the wayside and appear "foggy." Why does the plastic material(s) for headlights get this way, compared to the rear lights housing?
I think all the light covers are fading over time but the headlights are clear and so it is more obvious when they fade compared to the tail lights that have pigments. The other thing is the UV-light exposure; the headlights gets more light compared to the tail lights because of their angle.
By the science, MOST, plastic headlights and taillights (on the same car) will be made with different material. Front headlights are usually made with one called polycarbonate, which is strong impact resistant and such, unfortunately also means that it has poor UV resistance, and will fog up over time.
Taillights on the other hand are typically made from acrylic. Acrylic does not have the strength or impact resistance of polycarbonate. But it is FAR more resistant to UV.
Often taillights are placed in such a way that they are not exposed to direct sunlight as much.
On my Volvo the tail lights also fade - because they're made of the same material and placed similarly high.
It's so bad that even the actual red part inside of the tail light has faded and became red-pinkish.
But on a lot of cars, as @bruceree, has said - the tail lights are made of a different type of plastic.
Much more brittle, but less prone to fading.
This is merely a guess. Front headlights fade more than rear taillights because there is so much tiny debris hitting the front headlights over time. since we drive 99.9% forwards, most of the debris will hit the front, whereas the back is relatively unscathed.
