How much landscape lights cost in electricity will depend on several factors, including how many bulbs are used and how long they are on each night. Electricity usage is measured in kilowatt-hours (kWh). In 2021, the national average cost per kWh was 14.2 cents. Running your landscape lighting 5 hours per night, dusk until midnight, with 20 8-watt lights in a moderately sized landscape lighting design, you’ll use 18 kilowatts of electricity per month, costing less than $5 a month. If you have outdoor lights on motion sensors, that cost will be even less. That’s substantially lower than the $20-25 that incandescent or halogen bulbs cost to run.