The first thing we tell people when it comes to using Christmas lights for year-round applications is that you generally won’t get more than 12 to 18 months due to weather, UV, etc. UL will only rate any Christmas light set for 90 days or less of continual use. However, we do often use lights on year-round applications, but rather than getting 5 or 6 seasons from a set, we only plan on getting 12 to 18 months. Some sellers will claim that their lights will last for years, even on year-round applications, but even the best commercial grade lights simply can’t hold up to long term UV exposure.