Laguna Pressure Flo Model 2100 PT 1521, PT-1521 UV-C Germicidal Bulb for 20 Watt UV Bulb Effective Hours Rating: 10,000hrs - Ultraviolet Germicidal Light Bulb Base Type: 4pins ONE END Length: approx: 14.1" Bulb Type: T5 Style Quartz Glass For Laguna Pressure Flo 2100