This Caprock brand lamp is 100% compatible with the Sterilight S330RL OEM lamp selling at a much higher price, but is not made by Sterilight. The lamp has a special multi-step 4 pin base.

It measures about 330mm (about 13 inches), excluding the four pins on the end of the lamp. Its peak output is at 254nm (UV-C).

It can be used to repalce the OEM lamp in these and other systems:
Aqua-Pure Water Conditioning 5605833
Aqua-Pure Water Conditioning 56058-33
Aqua-Pure Water Conditioning APUV-2
Cuno 5605833
Cuno 56058-33
Cuno APUV-2
Evoqua Water Technologies LLC W2T365400
Heraeus AAE1418
Heraeus LP4735
Hydro-Safe HSRL-13
Hydro-Safe HSUV-SS-2
Hydro-Safe HSUV-SS-2-1
Hydro-Safe HSUV-SS-2-2
Nortec 254-4412
Nortec MHTC
R Can S2Q
R Can S2Q/2
R Can S2Q-Gold
R Can S2Q-Gold/2
R Can S2Q-PA
R Can S2Q-PA/2
R Can S2Q-PV
R Can S330RL
R Can SC4
R Can SC4/2
R Can SSM-17
Siemens LP4735
S2Q
S2Q/2
S2Q-Gold
S2Q-Gold/2
S2Q-PA
S2Q-PA/2
S2Q-PV
S330RL
SC4
SC-4/2
SSM-17
Ster-L-Ray 05-0566
Sunlight LP4735