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.