A town council is considering replacing the old vapour lamps on its streets with light-emitting diode lamps. An engineer argues that the change will cut the council's yearly spending on street lighting even though the new lamps cost more to buy, because ______. Which of the following best completes the engineer's reasoning?

The claim to be supported is that a higher purchase price still leads to lower yearly spending. Only lower running cost and a longer life can do that, since together they cut both the electricity bill and the frequency of replacement, outweighing the one-time extra cost. The number of manufacturers, the complaints about dark streets and the age of the present lamps say nothing about what the council will spend.