couple coats of a good sealant will do the job. most premium sealant are highly resistant to UV and infrared radiation. Durability is measure in months and since you will have a film over them so you should be good.
IMO... I think there are way too many owners who forget about putting a coating of protection on their headlights while they are waxing or applying sealant to their cars.
i hope this helps....
Here is one. BFWD
http://www.autogeek.net/blackfire-we...d-sealant.html