How Dimmers Save Energy

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Do dimmers really save on energy use?

Key to answering this question is understanding how dimmers really work.

Many consumers, and even a few electricians, think that dimmers work by converting unused electricity to heat at the dimmer switch.

It's true that many old rotary dimmers worked this way; they were rheostats that took the excess energy when dimmed and converted it to heat.

Today's dimmers use a "Triac Switch". When dimmed, these switches cut the flow of power to a light fixture up to 120 times a second.

While the circuit is switched on and off many times a second, the human eye and brain doesn't register this flickering. What we see is a constant light output.

And dimmers do save. Dimming your lights an average of 50 percent can cut your electric use a whopping 40 percent over time and make your bulbs last 20 times longer!

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  • During my break yesterday, the question do dimmers save money came up. One of my managers said they all use resistors to dim, so the energy would be lost to heat. Thank you for this blog as it has helped justify my investment in lutron dimmers.

    When I did more search realated to “Triac Switch” I found the following useful information.


    The triac is the key to dimming. This dimmer component actually turns on and off very rapidly - 120 times per second. The longer the light is ON versus OFF the brighter the light output. By the same logic the longer the light is OFF versus ON the lower the light output.


    When the light is off, no energy is being used. The longer the triac is off, the lower the light output, and the greater the energy savings.

    Dimming the Lights Saves electricity Makes incandescent bulbs last longer

    0.1 0.1 2 times longer  

    0.25 0.2 4 times longer

    0.5 0.4 20 times longer

    0.75 0.6 > 20 times longer

  • If you turn the dimmer so the light goes down, but not turn it so it clicks completely "off" is it still using electricity?

  • Alan - thanks for your comment. To your question, yes, a dimmer turned down but not completely off will continue to use a trickle of energy. It a very, very tiny trickle, however, so small that it would be mere pennies over the course of a couple of months.

  • Excellent question Callin!

    I posed your question to our resident bulb guru, buyer Hugh Prosser. Here's what he had to say:

    "Obviously a 25 watt bulb will use half as much electricity as a 50 watt bulb. However, when it comes to home lighting we should consider a couple important things, including one you may not expect!

    If you only need the light of a lower wattage bulb all the time, then go ahead and use a lower wattage bulb. However, if you ever need more light, having a higher wattage bulb on a dimmer is of great convenience.

    Greater lighting control helps a homeowner enhance their living spaces. We have wall dimmers that feature presets. The homeowner can set the dimmer to only go to 50% each time it's turned on. When more light is needed, simply tap the dimmer again and it will go to full brightness.

    Furthermore, there may be situations when the homeowner wants even less than 50% brightness. Having a dimmer makes this easy – certainly easier than changing out the bulb for an even lower wattage.

    Now let's consider the issue of bulb life. All bulbs are sold with an average life expectancy. For example, a 25 watt regular household bulb from G.E. states an average life of 2500 hours. At 5 hours of use a day this bulb will last approximately 500 days, or nearly a year and a half.

    However, bulbs that are on a dimmer enjoy a minimum of a 50% increase in life span!

    Here's why: A great deal of bulb stress occurs when they are first switched on. The household electrical current hits the bulb's delicate filament all at once.

    A quality dimmer does not allow this to happen. Over the course of a few milliseconds, the dimmer ramps up the current until full brightness is achieved.

    This is less damaging to your bulbs. While the homeowner will not notice this slight delay, they will notice that they are not changing bulbs as often!

    In conclusion, using dimmers lets you save energy and extends the life of your light bulbs. Plus, it enhances your home by putting lighting flexibility at your fingertips."

    Thank you Hugh!

    Find everything you need in our selection of light bulbs and dimmers.

  • Is it better to just by less wattage bulbs to save energy rather than dim a higher wattage bulb.  In other words, if you are dimming a 50 watt bulb to half, why not just buy a 25 watt bulb.  Does that save more energy

  • how can you tell which one is triac dimmer which one is the old type? I bought this dimmer on Amazon, the product description doesnt tell you what type it is.


  • Lee - unless you purchased an old-fashioned rotary dimmer, all modern dimmers have a triac switch.

  • Adam -- I enjoy this discussion.  Your feedback to Callin about the customizability of lighting levels that dimmers provide is excellent -- that is the reason I use dimmers.

    However, to say that they prolong the life of the lamp by ramping up the current is misleading.  The controller in the dimmer is just turning down the frequency of the electical signal sent to the light.  Also, incandescent lights that are normally dimmed are not particularly sensitive to being turned on and off frequently with a regular switch.  Your argument for customizability is good, but I think the extension of bulb life argument is weak at best, unless you have studies that prove otherwise.  

  • Ray,

    Actually, frequency is constant. It alters the duty cycle. If you think of the sinusoid as a hill, it turns of before you get to the tail(right) end. Therefore reducing the area under the curve.  

  • Ray - we posed your question to Robert Nachtrieb at Lutron. Here's what he has to say... "Lamp life extension is based on physical properties of tungsten: the evaporation rate decreases dramatically with temperature. You can look at the IESNA handbook for the technical specs. (See "Light Souces pg. 6-14".) In our own halogen dimming experiment, we saw some lamp types systems last more than 60,000 hours.  If you're interested, look for my presentation at the IESNA meeting last November."

  • I agree that using dimmers extends the life of the bulbs.  We moved into our home in July, 2006.  Since then we have changed light bulbs in every room, but I recently noticed that not one bulb had burned out in our family room which is on a dimmer. Just last week the first bulb in our family room burned out. We have the family room lights on every night and often every morning, so I don't believe the bulbs would have lasted over three years if they weren't on a dimmer. 

  • I installed 8 can lights in my Great room with dimmers back in 1986 when I moved in. They have been on EVERY night since then and have NEVER burned out.  That has to be some kind of record!! Dimmers do save the bulbs at the very least. They are the plug in type if that make any difference.  I don't know.

  • We installed 5 eyeballs with 100W floods in the cathedral ceiling of our bedroom in 1984.  They are used every day and night. They are on dimmers without presets (0-100-0%) To this day we have not had to change the bulbs, thankfully!  I am sure it is because of the dimmers.

  • That's a great story, thanks for sharing it!

    Using dimmers on hard-to-reach ceiling lights or light fixtures is a great way to extend the life of your bulbs.

    Should any of these bulbs ever burn out, you might want to think about long-lasting CFL bulbs or LED light bulbs as replacements, but just make sure that you purchase dimmable CFL or LEDs to work with your wall dimmer.

    Thanks again for the comment!

  • I recently put a non-dimmable CFL in my ceiling fixture which is controlled by a new Lutron dimmer. I obviously can't dim it but I didn't have a dimmable bulb on hand. There is a slight buzz at the dimmer and at the circuit breaker. Question: Is it safe to do what I did or is this a fire/electrical hazard?

How Dimmers Save Energy