Sun: Yes. But same for front and rear, see below
Headwind: I like it!
Heat: Another good one. From light bulb or engine?
Clear poly: I am comparing clear front and clear rear. But I don’t know what they are made of
Geometry: This will affect sun exposure and wind. But I have upper and lower front lights, totally different geometry and same oxidation
- Most lamps are made of Polycarbonate due to its durability wrt to impact, along with ease to manufacture smooth surfaces
- Heat I would say mostly from light bulb, I see the engine heat as a second order effect (given diffusers away from the front of the lamp).
- Bulb Wattage would be another factor, which is implicit in the Heat, as the low-high is usually 55W-75W for front whereas idle-break is 10W-22W for rear
- I think condensation/humidity within the casing would also have an impact
But I'd put my money on Heat and UV degradation as the likely culprits here.
M