Installs in-line as a stand alone fixture (cannot be submerged).  

Light tube can be installed in BF4000 filter. 

18' cord. 

Cal129: 18 Watt 
For ponds up to 2,000 gallons; 1000 gph

Cal131: 36 Watt
For ponds up to 4,000 gallons; 2000 gph.