How Much Does It Cost to Leave Lights On All Night?
Leaving lights on overnight is something many people do without thinking much about it. Whether it’s porch lights, hallway lights, or forgetting to turn something off before bed, the question often comes up: does it actually cost anything meaningful? Below is a breakdown of how lighting costs are calculated, realistic examples for common bulbs, and when the cost is noticeable versus negligible.
What affects the cost of leaving lights on
The cost of leaving lights on depends on a few simple factors.
Type of light bulb
Different bulbs use very different amounts of electricity. Older incandescent bulbs use much more power than modern LED bulbs.
Wattage
Wattage tells you how much electricity a bulb uses while it’s on. Common household bulbs range from about 5 watts to 60 watts or more.
How long the light is on
Overnight use is typically assumed to be 8 hours, though some lights may be on longer.
Electricity rate
Electricity is billed per kilowatt-hour (kWh). Many households pay between $0.15 and $0.30 per kWh, depending on location.
How lighting electricity cost is calculated
The basic calculation looks like this:
Wattage ÷ 1,000 × hours on × electricity rate = cost
This allows you to estimate daily, monthly, or yearly lighting costs.
Real-world cost examples
Leaving a 60-watt incandescent bulb on for 8 hours
0.06 kWh × 8 hours = 0.48 kWh
0.48 kWh × $0.20 = $0.10 per night
That’s about $3 per month for one bulb left on overnight.
Leaving a 10-watt LED bulb on for 8 hours
0.01 kWh × 8 hours = 0.08 kWh
0.08 kWh × $0.20 = $0.02 per night
That works out to roughly $0.50 per month.
Leaving a 5-watt LED bulb on for 8 hours
0.005 kWh × 8 hours = 0.04 kWh
0.04 kWh × $0.20 = $0.01 per night
That’s about $0.25 per month.
What if lights are left on all day?
If a light is left on continuously for 24 hours, the cost increases, but modern bulbs still use relatively little electricity.
A 10-watt LED left on all day:
0.01 kWh × 24 hours = 0.24 kWh
0.24 kWh × $0.20 = $0.05 per day
Around $1.50 per month
Average number of exterior lights on a home
Most homes have 3 to 6 exterior lights, commonly including front entry lights, garage lights, side or walkway lights, and a rear door light. Some homes may have more, especially with landscape or decorative lighting, but a small handful of fixtures is typical.
If those exterior lights are left on overnight, the total cost depends heavily on the type of bulbs being used.
For example, if a home has five exterior lights using 10-watt LED bulbs and they are left on for 8 hours overnight:
Total wattage: 50 watts
0.05 kWh × 8 hours = 0.4 kWh
0.4 kWh × $0.20 = $0.08 per night
That comes out to roughly $2.50 per month.
If the same five lights were older 60-watt incandescent bulbs:
Total wattage: 300 watts
0.3 kWh × 8 hours = 2.4 kWh
2.4 kWh × $0.20 = $0.48 per night
That’s closer to $14 per month just for exterior lighting.
This shows how the number of lights matters, but bulb type is usually the biggest factor in total cost.
When lighting costs add up
Lighting costs become more noticeable when:
Older incandescent bulbs are used
Multiple lights are left on at the same time
Lights are left on 24 hours a day
Electricity rates are higher than average
In homes with many lights left on overnight, small costs can add up over time.
When leaving lights on is usually negligible
The cost is usually minimal when:
LED bulbs are used
Only one or two lights are left on
Lights are on for overnight hours only
For many households, the cost of leaving a single LED light on overnight is barely noticeable on a monthly electric bill.
How to estimate your own lighting cost
To estimate your own cost:
Check the wattage printed on the bulb
Estimate how many hours the light is on
Look up your electricity rate on your utility bill
Repeating this for multiple lights gives a clearer picture of total usage.
The bottom line
Leaving lights on overnight does cost money, but for modern LED bulbs, the cost is usually very small. Older incandescent bulbs use more electricity and can add up over time, especially if multiple lights are left on regularly. Understanding the wattage of your bulbs makes it easy to estimate whether the cost is negligible or worth paying attention to.