Energy = Power x Time, and energy use is measured in kilowatt hours (kWh).  Your utility bill will charge you per kWh which is 1/1000 of a Watt multiplied by the number of hours used (or “on”).

Therefore if you have an older technology in operation, for example the 400W metal halide bulbs in your parking lot, and you have them on for a standard 7 hours/day (dusk ‘til dawn), you are spending 400W / 1000kW x 2548hours/year x $0.17/kWh = $173/year on that one fixture.

If you replace that one fixture with an LED equivalent that operates with 150W, you will spend

150W / 1000kW x 2548hours/year x $0.17/kWh = $65/year

Simple math will tell you that you will save $108/year if you replace that one fixture. This does not incorporate any savings on the maintenance of those new fixtures, considering that many LED fixtures have a life of 10 years.

Written by: And Laemmel