Fisher is correct. You can use one cathode only if you wish, though the inverter supports 2 and this deal includes the 2nd bulb.
The description has been updated just for MichaelD:
1 x Acrylic tube around each bulb (for protection of the cold cathode tube)
The description has been updated just for MichaelD:
1 x Acrylic tube around each bulb (for protection of the cold cathode tube)