Genuine US Water Filters replacement lamp for the USWF-4C151 and USWF-4CR2 UV systems. USWF lamps are backed by a one-year, no-hassle warranty. The USWF-RL420HO boasts a 10,000 hour lamp life, which means low hassle and maintenance for 13 months between lamp changes. After 10,000 hours the UV light weakens and isn't strong enough to properly treat your water. Replacing your lamp annually ensures optimal system performance. Safety Note: NEVER look directly at the UV lamp when it is powered on. Follow the instructions carefully to avoid injury to eyes and skin. After a year, UV light weakens and isn't strong enough to properly treat your water. Replacing your lamp annually ensures optimal system performance. Includes 2 replacement o-rings.