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Ask the Energy Expert
Energy Expert

About "Ask the Energy Expert"

Craig Muccio runs FPL's Conservation Research & Development Program and crunches the numbers to figure out how you can save by managing your energy use.

Your questions on energy-related topics can be submitted anytime to our Ask the Energy Expert blog. Just click here to submit your question, and if chosen, it will be answered here

Turning a Light Off Versus Leaving It On

I was once told that it takes more energy to turn a light on and off than it does to just leave it on for 10 minutes or so. Is this true?

There is a little extra electricity involved in turning a light on due to more power needed during startup. However, the amount used is more like leaving the light on for a couple of seconds of normal light operation. Therefore, we recommend turning off a light whenever it is not needed.

One thing that you may want to consider, though, is the lifespan of the bulb itself. The cost effectiveness of turning off lights depends on the type of bulb. All bulbs have an average operating life, which depending on the bulb type could be affected by how many times they are turned on and off.


Incandescent lights should be turned off whenever they are not needed, because they are the least efficient type of lighting. Ninety percent of the energy they use is given off as heat, and only about 10 percent results in light.


For CFL and other fluorescent lighting, the answer depends on the frequency and length of time you turn your lights on and off. The operating life of CFL and fluorescent bulbs is affected by the number of times they are switched on and off. You can generally extend the life of these bulbs by switching them on and off less frequently. You’ll save energy by turning the light off, so you’ll need to determine if the savings outweighs the cost of replacing the light bulb if it fails early due to frequent switching.


LEDs are a good option for lights that are switched on and off a lot because the operating life of an LED is unaffected by turning it on and off. It’s always best to turn off LED lights whenever they are not needed.

For more information about the different lighting options for your home, please read my previous blog post on this topic.

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Comments [55]

Alan Kohlhaas // March 8, 2013

I have been told that turning down the thermostat on a heat pump does not save money for heat since when the heat goes backup the backup heat comes on to bring up the temperature thus eliminating the saving. Is this true?

Enrique // March 8, 2013

What would be the best lights to have an energy efficient home and save money?

Geoff Church // March 8, 2013

Hey, you really want cheap electricity bills. Here are the tips. If you live alone, especially.
The hot water heater will burn tons of electricity so, fit a timer allowing it to come on to heat enough water for each day. Cheaper yet, turn it on and off as needed. Wash dishes by hand under running water and use dish soap. Good for singles as you only use odd plates, dishes, cups or mugs and glasware on a minor scale. Again, dishwashers burn tons of energy. Of course, use energy efficient LED and CFL lighting. Switch off appliances fully, do not leave them in standby. This will also protect them from power surges. Instead of turning on the heat when it gets chilly, put an extra cover on the bed and extra clothing when up and about. Vice vers when it is hot. Don’t let yor A/C run when it is not needed and turn the stat up a couple of degree. You’ll acclimatize quickly to the change and suffer less colds etc. If you have a pool keep the time the pump is running to a minimum.
Just be prepared to put some effort into these money saving tips and it will pay dividends.
My power bills are less expensive than my water around $30 a month in winter and usually no more than $70 in summer. That is running a pool pump too. I have the proof of these savings over the last 5 years. So, you are getting these tips from an experienced (minimal)consumer.

Cheers mates…

Richard Rossi // March 8, 2013

What about leaving a phone charger in the socket when not charging? More energy used?

Dorothy // March 8, 2013

Does it cost more to turn off my computer when not in use — or to leave it on until use is resumed?

Thanks. Dottye

Pauline.goldberg // March 8, 2013

If I have old fashion fluorescent lighting in my kitchen that has a ballast what is the advice for turning them on, length of time kept on,etc. So far I’ve lived here for ten years and haven’t replaced any of the long,5ft lights or ballast?


Ps Sometimes,rarely, one of the lights doesn’t come on immediately ,but turns on within a few minutes

Gwen Nastasi // March 8, 2013

When I am doing housework, I have all my tv’s on so I don’t miss the news as I go from room to room constantly. The husband is always telling me that I am wasting energy. Am I and if so, how much energy do televisions use?

Thanks for your help!!

John Nicoletti // March 8, 2013

Very interesting article. I was always a favorite of simply turning a light off, when not in the room.Why would we leave a light on in any room that is not occupied.? The type of bulb, in my opinion, is not relevant.

Joe // March 8, 2013

Very good information.

Mike D // March 8, 2013

I was always told that if a fluorescent light was going to be turned-on again within one hour, then it should be left ON. Is that roughly correct?

FL DOC // March 8, 2013

The TV show, Myth Busters did a segment on one of its shows on the the savings involved by shutting a light off when leaving a room. They did extensive testing on both incandescent lighting and florescent lighting.

Their test results showed that the “burst” of electricity used when turning a light back on is about 35 hundreds of one second worth of electricity. Their conclusion was, “It always pays to shut the light off when leaving a room. turn .35

bob // March 8, 2013

I used a compact fluorescent in the refrigerator and it only lasted for a few months, so use one of those old style bulbs, it’ll get hot but last much longer.

Lois Jones // March 8, 2013

I, too, had heard the myth of turning lights on and off to save electricity which over the years referred to incandescent bulbs as you decribed. However, now that times have changed and we are using various types of bulbs, I am happy to have the detailed information you provided.

While these may seem to be simple questions, it serves a good purpose to have correct information from FPL experts.

Thank you for sharing.

Lois Jones

Jean // March 8, 2013

Please tell me if I should leave some fans on while I am away for six months in order to have better circulation in my condo. I leave the temperture setting at 79 and my humidistat at 70%. Does running the fans help prevent mold?

Steven C // March 8, 2013

Incandescent light bulbs generally fail at turn-on and less often at turn-off.

LED lighting is subject to migration of the atoms in the semiconductor junction that produces the illumination. This only occurs if the LED Lighting is ON. Again, over time, this migration in LED Lighting causes them to become less bright (takes years). It is always best to turn off LED Lighting whenever they are not needed. Dimmable LED Lighting is less susceptible to this migration when dimmed. One option is to dim the LED Lighting to the dimmest setting and leave it on if you do not wish to turn it off. Make sure your LED Lighting is DIMMABLE though.

ROBERT KOVACK // March 8, 2013




Steven C // March 8, 2013

The thing that must be considered here in Florida is that we are mostly Air Conditioning out HEAT. Incandescent and CFL’s produce a remarkable amount of HEAT into the living space – even if in overhead lights. You must consider the removal of the heat in the equation and that is a VERY LARGE FACTOR.

LED Illumination. I was absolutely astounded at how much my electric bill dropped when I switched to all LED lighting from (Flourescent – CFL – Incandescent). WOW! Expensive to buy but LONG LASTING and ENERGY EFFICIENT in the extreme ESPECIALLY because of the LOWER HEAT in the LIVING SPACE.

I do PREFER INCANCESCENT (PAR30 – as called for by the fixture) Bulbs in my bathroom ceiling cans because of the radiant heat they produce – especially after I take a shower. I am particularly careful to minimize the time on though and I use a dimmer most of the time to reduce the light and HEAT. In my Kitchen and Guest Bathroom, I have opted for PAR30 LED bulbs and they have saved me a TON of $$$ on Electricity for A/C and Lighting. The savings on Electricity has easily been recouped on the expensive purchase price in less than 1 year of operation. WOW!!! And the LED PAR30 bulbs will last for many years as opposed to about a year or so for the Incandescent Halogen Bulbs. The biggest savings is the distinctly less HEAT that is injected into the living space that then must be A/C’d out which is MUCH MORE EXPENSIVE.

Diane Drake // March 8, 2013

I think this is wonderful thing FPL is doing. I am always looking for tips to lower my FPL bill and use less energy. Thank you. now that I found your site I will be looking for more tips. Thanks Again Have a Great Day!

Laura // March 8, 2013

Thank you for the info. It’s very helpful! By the way, LED lights are still very expensive but all considered, may cost the same as CFL.

MARILYNN TAFFEL // March 8, 2013


Jan // March 9, 2013

Thank You… it’s great information!

mitchall smith // March 9, 2013

Def helps clear up some things for me. Im an avid electicity saver..i even unplug nitelights..my thing is..why pay for a light to run when its not needed!

Susan // March 9, 2013

I have been able to save hundreds of dollars a month just by turning my breakers off. I have a 3000 square foot home and my power bill runs $59.00 a month. If you really want to save energy and money turn those breakers off to the room you are not using during the day, and watch your bill go down!

peggy // March 9, 2013

Which uses less energy: 1000 watt micro for 10 to 15 min vs a slow cooker on high/300 watts for 4 hrs?
Trying to determine low cost cooking. I have an electric burner that uses 750 watts besides a rice cooker (can be used like a slow cooker) that is 550 watts.
How does one figure which process uses the least energy. For instance, heating up a cup of coffee. I usually use the micro for a min or should I use the electric burner?
Am I better off just using the micro or use the other devices mentioned above?

Joyce Varisco // March 9, 2013

This is for Patricia H. To save more money on electricity, UNPLUG lamps, the toaster, the coffee pot, etc. when not in use. This will really add to your savings.

clara sutton // March 9, 2013

I live alone and use hot water sparingly..would i benifit from turning off my water heater for overnight and ha

francoise despres // March 9, 2013

We are snowbirds, like many customers of FPL, every spring time a lot of specialist… Give tips (before heading north). AC open or not, degree 80f or 85f, fan on or off, isolation with styrofoam for windows, etc. Etc., now I want to ask you the Specialist, some tips how to close my house for 6 months without surprises when we come back. Thank you.

Faith // March 9, 2013

Very helpful.

Deanna Rosier // March 9, 2013

I keep lights off as much as I can and this does help

Jan Griffin // March 9, 2013

How does this apply to both computers and TV’s? Turn them off and on or leave them on?
Thank you

Robert Winsler // March 9, 2013

Our Homeowners Association believes that leaving our street lights on all the time saves money. There are almost 200 lights and they are compact fluorescent bulbs in each lamppost. Does it save money? Can FPL make a study to determine once and for all?

Frank Squire // March 9, 2013

Use timers and or photo light sensing units to turn outside lights on and off. I see so many times lights on outside of homes during the day. People just simply forget to turn them off resulting in energy wastage.

Phyllis Rohwedder // March 9, 2013

I found lights on a dimmer switch last longer if they are dimmed on low instead of off. My bulbs last a great deal longer if I just leave some on and only turn off once a day. Nite lights I leave on all the time. they last much longer.

Donna Yezzi // March 9, 2013

Very important. Info thank you

Donn Foster // March 9, 2013

I have solar hot water and a 4.9 kw solar electric system. I’d like to add a wind turbine of some nature but everybody I’ve researched indicates that my area code (34243) does not get enough wind. Could you please explain this in more detail?

terri // March 9, 2013

if an appliance is off but plug in does it draw any energy.

Cecilia // March 10, 2013

Is it true that when you open the refrigerator door it consumed more electricity if you leave it open for a few seconds than open it and closing it right away?,

Frances Vancer // March 10, 2013

This is excellent information that is very useful. Thank you.

victor gust // March 10, 2013

Is it true that the cost of having lights on in the house is the light bulb not the electricity. I was told that the cost of electricity with the lights on, is very very small. Am I right?

Thanks for your reply

Kathryn A. Agruso // March 11, 2013

What do CFL,Flourescent and LED bulbs each look like?

Theresa Murphy // March 11, 2013

I am wondering. I have heard that electonics, such as laptop computer or surge potectors we use for our (RC model car batterys). Are they drawing power if they are drawing power,even if they are plugged in but turned off?

MARIA MARTINEZ // March 12, 2013


Tom Pritchard // March 12, 2013

I understood that if you had (or still have) an old style conventional flourescent light installation, if you weren’t going to leave it off for at least 15 minutes, it wasn’t worth the bother to turn it off. Older flourescents had ballasts that consumed a considerable amount of energy to initally power the bulb up, hence the 15 minute suggestion. Have the ballasts been improved? I understand the dynamic of increasing the frequency of turning them on and off diminishing their overall useful life.

GARY MCIVER // March 13, 2013


patricia // March 14, 2013

Is it true that you save by unplugging anything not being used. I was told even if the lamp is not on its still drawing energy. Also to unplug chargers when they are not being used.

Elizabeth Hughes // March 19, 2013

Good info in this reply. Have been looking at LED’s as replacement for kitchen spotlights – incandescent (hot) and this has convinced me that LED’s are the way to go. Thanks for this info.

Monique Marion // March 19, 2013

Born & Raised in Europe, I was told by my parents as a very young age to turn the light off when living a room in our house. So this is nothing new for me. After 44 years living in the US, I always practice my parents old ways and teaching somebody living here this is a task! Too much waste in this country with everything and parents don’t do there job, it’s a shame….

Randall D Godfrey // March 23, 2013

The guidance I was given is that you never turn the temperature down more than five degrees. I think the same applies for electrically heated (resistance heating, heat strips, etc.) homes too.

Barbara Bommaarito // March 29, 2013

Fans verses air conditioning.

I know it costs more to heat than to cool but what about using fans instead of the air. I have ceiling fans in all my rooms and but my husband says that it is more effecient to turn off the fans in roooms that we aren’t using. I say the roooms stay cooler with the fans on at all times.

Steve // April 8, 2013

You neglected to mention how big in square footage is your domain. That in it self means a lot as to savings. Also there is a point as to how much you can turn the ac up, the higher the temp. in the house the higher the humidity level. I find that 78 in the summer is a comfort zone for me, rising the temperature any further will cause other problems like musty order and over a period of time mildew in certain areas.

Thierry Smits // July 18, 2013

What’s the cost $ of running 6 flood light 100 watts each for 4 HRS each day?

Michel JJA Riendeau // August 6, 2013

Use a solar water heater with hose on top and a water tank located over the thermo pump exterior emission you will have heat water for free.

Also I imagined that it is possible to create natural gas in a very strong tank at less 65 degree (-65 F) load one fifth carbonic ice and with water eletrolize then take the gas from the hydrogen electrode to load the tank in lowering more and more the temperature to up to less 185 (-185 F) and if the hydrogen turn liquid on the contact of the carbonic ice and the carbonic ice disappear then you encounter a liquid at less 185 who is LNG Liquefied Natural Gas.

ledlights // August 9, 2013

Most people prefer to buy LED lights in comparison of traditional bulbs because led lights produce less heat and saves energy. LED lights are cost effective and energy efficient diode. The installation of light emitting diodes is also very easy.I once buy from OKLEDLIGHTS (dot) COM is nice .

Chris // October 28, 2013

Does a lamp that is plugged in but not turned on use energy??

Linda Dube // March 4, 2014

What would be the best replacement for florescent lighting in my basement back home. Thanks,


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