"Important" is a relative matter of course, and surely light bulbs were not as ubiquitous in 19th century as they were later, but e.g. London had 2.5 million li

"Important" is a relative matter of course, and surely light bulbs were not as ubiquitous in 19th century as they were later, but e.g. London had 2.5 million light bulbs at the end of 19th century. That is not insignificant.