Basically the linear tubular light is called Tube Light. A FTL (Fluorescent Tubular Lamp).

This ismainly available in 3 diameters. The old 40/20watt with 38mm dia (called T12 lamp), 36/18watt with 26mm dia (called T8 lamp) and 28/14watts with 16mm dia (called T5 or T16 lamp).

Apart from lamp the ballast used with the same also consumes some power. Ultimately you pay is for the switching ON of the lamp. That means for the power consumed by the lamp as well as the ballast.

The power consumption of the lamp is constant, but the consumption by the ballast varies as per its quality and construction (Aluminium wound/copper wound or electronic).

The Aluminium wound is most inefficient and the electronic one is the most efficient with least power consumption.

Now, the total energy that the tube light consumes is the sum of the consumption by the lamp plus the ballast. Now multiply this by the burning hours divide by 1000 to arrive at Units consumed.

However the advent of LED as the light source is making almost all other light sources as the things of past.