unless you got some grease, or road tar, you do not need chemicals at all, use wet microfiber cloth to wipe them clean, every time you use some chemicals, you are risking damaging your UV coating.
I haven't gotten much grease or road tar on the headlamp, but insect guts can be tough to remove especially when they've been baked on for a while. The plastic cleaner/polishes I've been using do a good job of cleaning, but I wasn't sure what effect the 'polish' part would have on the UV coating.
Use plenty of liquid -- whether it's soapy water, car wash solution, Windex, Simple Green, or etc. You are washing a clearcoat, harder than that on a car body.
The way I've been cleaning them is spraying a generous amount of plastic cleaner/polish on a microfiber cloth or directly on the headlamp and then gently spreading the stuff around first before applying cleaning pressure. Good to know that the clearcoat is pretty tough.
If anything, it's the microfiber cloths themselves that can cause problems, as sometimes the tiny fibers shed (in not insignificant amounts) and then get stuck on the lens requiring multiple cleaning passes to remove. Brand new cloths don't seem to do this nearly as much as ones that have been washed to be reused.
Maybe the cloths I've been using are just junk (Amazon stuff).
also...if you can park front end away away from direct sunlight. From my observation, those that park towards the sun path always have much quicker degradation of the coating.
The motorcycle's five years old with about 55K miles and the headlamp lens has no hazing that I can see. It would look almost new except for a few small nicks from road debris. It's a weekend toy that is parked indoors when not used so I guess that helps.
If the headlamps need cleaned odds are good the rest of the car does as well. Give it a bath.
It's a motorcycle that doesn't have a windshield so keeping the safety critical components (i.e., external lighting) clean is easy enough that I just do it as part of my pre-ride check along with tire pressures, lighting and brake functionality, etc.