How Much Energy Does Turning Off the Lights Save?

"Remember to turn your lights off when you leave the room!"

You may have heard this phrase from your parents, grandparents or other adults while growing up. For many, turning off the lights when you aren't in the room was an essential task. But, does turning off your lights save energy and reduce costs on the electricity bill?

Keep reading to learn more and answer the pressing questions of how much energy turning off the lights saves and what are the benefits of turning off lights?

HOW TURNING THE LIGHTS ON AND OFF CAN AFFECT THE BULB

While turning the lights on and off doesn't affect the amount of power you use, rapidly hitting the light switch can affect any type of bulb's lifespan.

INCANDESCENTS

Turning incandescents on and off generally doesn't affect their lifespan. However, you've probably heard how inefficient incandescents are. Ninety percent of the energy an incandescent bulb uses produces heat, while the last 10 percent produces light. As consumers move towards LEDs and CFL bulbs for higher sustainability and energy efficiency, a large percentage of lightbulb sales still go to incandescents and halogen bulbs.

If you're still using incandescent bulbs in your home, you should turn them off whenever you aren't in the room. 

Thinking about switching bulbs? Check out our lighting energy savings calculator to see how much you can save when you go from incandescents to CFLs or LEDs. 

LIGHT EMITTING DIODES (LED)

Light Emitting Diodes, or LEDs for short, are the most efficient bulbs you can use for home illumination. Like incandescent bulbs, they are generally unaffected by the number of times you turn them on or off. 

Learn more about lighting your home with LEDs in our LED home illumination blog.

COMPACT FLUORESCENT LAMPS (CFL)

Compact fluorescent lamps were touted as the first energy-efficient alternative to the incandescent bulb but weren’t popular when introduced due to their high cost and fragility. As manufacturers developed a more durable, affordable and energy-efficient bulb, the LED took the mantle for the best form of illumination.

Businesses and consumers alike still use CFL bulbs, but rapid switching of the bulb affects its lifespan. Unlike incandescents and LEDs, CFLs require a small surge of energy when they illuminate completely. While CFLs require this small surge of power to light up, it doesn't negate the energy savings of turning off the lights.

Rapidly turning the lights on and off can lower a CFL's lifespan. The U.S. Department of Energy recommends leaving CFL bulbs on if you will be out of a room for 15 minutes or less and turning it off if you will be gone longer than 15 minutes. Other research has shown that you should turn off fluorescent lights if you are going to be out of the room for three to five minutes or more. Either way, don’t leave your CFLs burning all day to try to save energy.

CAN DIMMERS OR OTHER LIGHTING CONTROLS HELP SAVE ENERGY?

Dimmer switches can help save electricity depending on the type of bulb you use and if its design is compatible with dimmers. Dimmers reduce the number of lumens a lightbulb produces. Incandescent bulbs are less efficient when dimmed because they still use the same amount of energy with fewer lumens. Dimming an incandescent may elongate its lifespan, but it has limited energy-saving benefits.

CFLs and LEDs designed for dimming can be more efficient and last longer if dimmed. It's essential to get lights that are compatible with dimmers. If your bulbs aren't, trying to dim them can shorten their lifespan.

HOW MUCH ELECTRICITY IS WASTED BY LEAVING THE LIGHTS ON?

To determine how much energy you can lose by leaving the lights on, you need to know:

• How much energy your bulb uses. The bulb box should give you a wattage rating for the light bulb.
• The number of hours your bulb was on while you were out of the room. Develop a rough estimate of how many hours you leave the lights on per day while you aren’t in the room; multiply the estimate by 30 to figure how many hours per month you leave the light on
• How much your energy cooperative or public utility charges per kilowatt-hour. You can locate this information on your monthly energy bill.

Calculating the Cost:

• First, divide your bulb's wattage by one thousand to determine the number of kilowatts it uses every hour. 
• Then, multiply the kilowatts by the estimated number of hours your bulb was on while you weren't in the room. This will give you an estimate of the electricity lost. 
• You can multiply the number of kilowatt-hours by the amount your utility charges per kilowatt-hour to estimate the cost.

Here’s an example: Let’s say you have two 60-watt incandescent light bulbs in your bedroom, four in your living room and four in your dining room, for a total of ten bulbs. You regularly leave them on for 4 hours a day when you aren’t in the rooms. And your cooperative rate is ten cents per kilowatt-hour. See the calculation below:

60 x 10 = 600 total watts

600 / 1,000 = .6 total kilowatts

4 x 30 = 120 hours per month lights left on

120 x .6 = 72 total kilowatts wasted each month

72 x .10 = $7.20 wasted or that you could save each month by turning the lights off!  

Home illumination is vital to carry out our everyday tasks. However, we can always do a better job of keeping the lights off to save electricity and money.

For more information on residential lighting, visit our lighting efficiency page. Check out our contact page to get in touch with your local distribution cooperative.