Landscape Lighting Energy Cost: Calculate Your Estimate
Estimate landscape lighting energy cost by multiplying power, operating time, and your electricity rate. Use the system's actual input power where available; fixture wattage totals alone omit transformer and control losses.
The calculation
Annual energy in kWh = input watts ÷ 1,000 × hours per day × days per year.
Annual energy cost = annual kWh × electricity price per kWh.
A worked example
A system drawing 100 watts for six hours every night uses 100 ÷ 1,000 × 6 × 365 = 219 kWh per year. At an illustrative rate of $0.18 per kWh, its annual energy cost is $39.42. Your rate and seasonal operating hours may differ.
Compare a proposed retrofit
Suppose an existing system draws 300 watts and a proposed system draws 80 watts at comparable useful illumination. At six hours per night, the annual difference is 220 ÷ 1,000 × 6 × 365 = 481.8 kWh. At $0.18 per kWh, that is about $86.72 in annual energy savings.
These are illustrative measured-input assumptions, not promised savings for any product. Divide the installed retrofit cost by estimated annual savings for a simple energy-only payback; include maintenance and replacement costs separately.
Improve the schedule as well as the lamps
A timer that switches lights off when they are no longer needed can reduce operating hours. Check how that affects entrances and other areas that must remain illuminated. A lower-power lamp is not an improvement if its beam no longer serves the task.
Keep the comparison honest
Do not assume a low-voltage transformer itself reduces energy use or that all LEDs save the same percentage. Compare actual input power, equivalent useful lighting, and the same schedule. Check your utility bill for the applicable rate and avoid treating fixed monthly charges as energy savings.
How much does landscape lighting cost to run each month?
The following examples use six hours per night, 30 days and $0.18 per kWh. Input watts mean the entire operating system at the power supply, not a transformer’s maximum capacity. The rate is illustrative, not a national average or a quote for your utility.
| System input | 30-day energy | 30-day cost | 365-day cost |
|---|---|---|---|
| 40W | 7.2 kWh | $1.30 | $15.77 |
| 80W | 14.4 kWh | $2.59 | $31.54 |
| 150W | 27 kWh | $4.86 | $59.13 |
| 300W | 54 kWh | $9.72 | $118.26 |
Does a 300W transformer use 300 watts all night?
Not necessarily. Its capacity rating does not establish the actual draw of your connected lamps, controls and transformer losses. Use measured real input watts when available. Do not substitute VA directly into a kWh cost calculation; transformer-load planning and billed energy are different calculations.
What if the lights run longer in winter?
Calculate each season or month separately and add the results. For example, 100W running four hours daily for 183 days and eight hours daily for 182 days uses 218.8 kWh annually. At $0.18/kWh, that is $39.38 before any separately estimated standby use.
Use only the variable charges affected by consumption when estimating savings. Fixed service charges usually remain. For equipment that stays powered while its lights are off, include documented or measured standby use without counting it twice.
The watt-hours method is explained by Virginia Cooperative Extension’s energy-use guide. For choosing replacement equipment, use the LED retrofit checklist.
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- Kevin Simon