Which of the following variables is NOT involved in calculating the cost of running the lamps?

The variable that is not involved in calculating the cost of running lamps is the voltage rating. When determining the operating cost of lamps, three primary factors are considered: the number of lamps, the time they are in use, and the electric rate.

The number of lamps indicates how many units are consuming electricity, while time in hours tells you how long they are operated, allowing for the calculation of total energy consumption. The electric rate is the cost per unit of energy used, which directly impacts the overall expense incurred from running the lamps.

Voltage rating, however, does not affect the cost calculation itself. While it is important for understanding how lamps are designed and their electrical requirements, it does not play a role in the formula used for determining operational costs, which is usually derived from wattage (or kilowatt-hours) associated with the number of lamps and duration of usage.