Original Factory Replacement (UC100E1006) UV Bulb for Honeywell UV Germicidal Lamp - 18 Watt SnapLamp knob and bulb assembly. With this knob/lamp assembly, future lamp replacement will require only the new lamp (UC18W1004) as the lamp itself is removeable. Fits:Model UV100E1043 Single-Lamp Reurn Air Unit. Older Model UV100A1000 Return Air UnitReplaces UC100A1005 - (same bulb, blue handle rather than tan). Overall bulb length is 8½ inches, glass length measures 7½ inches. The bulb has has two glass tubes fused together and two filaments, each tube is ¾" in diameter.