But if you're Wal-Mart and use hundreds of thousands of bulbs, changing to CFLs can add up to millions in savings.
UPS recently made a similar discovery, finding that smarter route planning added up to enormous rewards:
At $4 a gallon, conserving 3 million gallons of gas translates to a savings of $12 million.
Company leaders figured out that sitting in traffic, waiting to make a left, burns way too much fuel. So they zapped as many left turns as they could from 100,000 truck routes a day.
Instead, drivers are handed computer-generated delivery routes that have them going in efficiently calculated loops, calling for left turns only when necessary.
"You start on the right-hand side of the street and you stay on the right-hand side of the street almost all of the day," said Dan McMackin, a former UPS driver who is now a company spokesman. "The only left turn you make is to come home."
According to the company, this simple technique saves an eye-popping amount of gasoline. "In the last year alone," a UPS release stated, "this system has shaved nearly 30 million miles off UPS's delivery routes, saved 3 million gallons of gas, and reduced emissions by 32,000 metric tons of CO2 - the equivalent of removing 5,300 passenger cars off the road for an entire year."