This purchase is for the bulb only and does NOT include the bulb sleeve (also pictured) The Pondmaster 12971 Replacement UV Bulb works with the Pondmaster Submersible 10 Watt Ultraviolet (UV) Clarifier. It is recommended to replace the bulbs every season for optimal performance. Don't wait for your light to burn out, replace yearly because over time the bulbs lose their effective light spectrum.\n