# Will switching to LED lightbulbs make a significant difference in my electric bill?

I asked Reliance Controls about a THP103 meter that I was having trouble with. Turns out that it's not a true RMS meter and thus is unable to give you accurate readings on a CFL or LED installation. See my other question: Why am I getting strange results when using a power meter to measure CFLs?

After explaining why I was testing a CFL (not seeing a noticeable difference in the cost of electricity being used) they replied with the following which I'm assuming isn't public knowledge because the average person doesn't have a degree in Electrical Engineering:

You may already have information on estimating the energy usage/utility charges, but here is a document that might assist in calculations if you are interested. The difference between a 100W incandescent light and a 15W CFL is pretty minimal when related to monthly costs, but that's just a generalization and there are many factors.

If both lights are on 24 hours per day, for 30 days in a month, the 100W bulb might cost about 5-6\$ more for that month than a 15W CFL. But if they are on only 12 hours per day, for 30 days, the difference is much less, maybe only 2-3\$ per month. Less than 12 hours per day will bring that difference closer as well. Maybe some of the formulas will help learn more about what could be bringing the bill up or down.

So, I'm looking for a way to bring down my electric bill and I'm leaning on the age old principle of simply turning off the lights when you leave the room. However, I work long hours and light is somewhat of a necessity unless I work by the glow of my computer screen. Plus I need a light for my chickens which require 16 hrs of light during the day and winter is setting in, and the simple fact that I live with 3 other people who don't know how to turn off the lights. One's 3 so he's excused until he can reach the switch.

Does anyone know if LED bulbs make any difference in terms of lowering costs to a noticeable degree?

• Which of your appliances are electric? such as an electric water heater.
– mike
Commented Oct 10, 2013 at 17:31
• Stove, fridge, freezer, washer, dryer but not the Water heater. That is propane. Commented Oct 10, 2013 at 17:38
• thanks. it might be interesting to have all lights turned on, and all other devices turned off (and unplugged if they draw power when off), then take readings off the main electric meter.
– mike
Commented Oct 10, 2013 at 17:49
• The point is that they'll save you much more than the cost of the lightbulb over the course of several years. But on a per-month basis that's still not a lot. Commented Oct 10, 2013 at 19:24
• There are other Factors, some people dont find LED bright or natural enough. But my house is 90%LED and I love it... what saves the most money? not replacing blown bulbs all the time my bulbs are rated 40 000 hours. Factor that in your costs also! Commented Feb 25, 2015 at 6:20

## 8 Answers

Say your electrical bill is \$100 a month.

Now say you have a refrigerator, a computer, a window fan and your light bulbs in your house as your only electrical devices. Everything but your light bulbs are on 24/7.

• Fridge: 725W **NOTE MOST FRIDGES DON'T ACTUALLY RUN 24/7 THIS IS JUST FOR EXAMPLE PURPOSES*
• Computer : 125W
• Fan: 150W
• Lights (on 8 hours a day, 100W)

• Fridge, computer and fan on all day = 1000W * 24h = 24kWh
• Lights on 8h a day = 0.8kWh
• Total daily usage = 24.8kWh

In that scenario your lights represent 0.8/24.8 or 3% of your daily electrical consumption.

If you replace your light with a 15W bulb, you've dropped from 24.8kWh to 24.12kWh a day, a savings of only 2.7% of your total daily consumption.

Addendum: I am not saying lighting is going to be 3% of your bill - I'm only making an example. You have to do the math - you have to figure out how much total power you're using (check electric bill) and then how much power your lights use (look at the bulbs and measure how long each one is left on each day) and that's your total % of energy for lighting. If that % is 15 then you can only reduce that 15%. You can cut your lighting costs in half, but half of 15% is only 7.5%.

• Yeah, so? My example fridge has a bad door seal. I'm making A POINT here! ;) Commented Oct 10, 2013 at 18:02
• good answer. simply stated: Why don't more efficient light bulbs lower my energy bill much? Because you weren't spending much on lighting to begin with.
– mac
Commented Oct 10, 2013 at 18:04
• @mike Are you deliberately missing the point of my answer? Substitute Refrigerator with "Thingamabob" - it makes no difference. The point is : if your lights only represent a tiny fraction of your total electrical usage, reducing how much power your lights use can only make a tiny fraction of a difference in your bill. Commented Oct 10, 2013 at 18:10
• @TheEvilGreebo, W is Watt, 1 Watt = 1 Joule/second. Watt is a measure of power. Multiply power by time to get a measure of energy used (energy could be measured in Watt-hours, which is handy here, a thousand Watt-hours is a kWh, which is what the power company likes to bill you for; 1 kWh = 3.6 Mega Joules).
– mac
Commented Oct 10, 2013 at 21:22
• I ran Kill-A-Watt for the past 24hrs on my full size fridge in my 66 degrees Fahrenheit home. Kill-A-Watt reported the fridge consumed 1030 Wh, or 1.03 kWh over that 24 hour period. So this fridge in a 66F kitchen draws energy equivalent to a 40W light bulb on 24/7, or a 100W light bulb left on 10 hours per day. The fridge consumes about 10% of my all-electric home's electricity, which is about 280 kWh per month.
– mike
Commented Oct 11, 2013 at 22:50

Everyone is saying, one way or another, that residential lighting is not a significant part of your electric bill. More efficient bulbs will eventually save you money, but depending on usage patterns and energy costs, this can take many years.

If you want to see significant change in your electric bill, you need to address the major consumers of power. The largest are typically resistance heating loads. Space heat, clothes dryers, cooking appliances. Better insulation and efficient lifestyle habits reduce heating loads. Newer appliances are more efficient than old. Even though you can see reductions in monthly bills, new appliances can be expensive, so the pay back period may still be quite long.

The other big consumers of power are large motors. Air con, fridges, freezers, shop equipment, etc. Once again, newer appliances are more efficient, but pay back times are still long.

The reason energy efficient bulbs are being pushed is everyone needs to buy bulbs, they are relatively inexpensive compared to the big power consumers. Almost anyone can afford efficient bulbs.

There's lots of ways to save energy, but unless you've been wantonly wasting energy all along, pay back periods are going to be long. The best approach IMO is to not replace anything until you need to, and only then consider energy efficiency, because then pay back time is based on the difference in cost between choices instead of replacement cost of something that is working, though not efficiently.

• "Everyone is saying, one way or another, that residential lighting is not a significant part of your electric bill. " - False. I explicitly made it clear I was not saying that. Commented Oct 11, 2013 at 9:57
• OK, my bad for generalizing. It was a cheap segue into my main point of chasing after big consumers to see any real reductions. It could have stood on it's own. FWIW, it is not explicitly clear to me you are not saying that. You provide a precise mathematical example, it appears to be up to the reader to decide what that means. No better way to present the issue IMO. Commented Oct 11, 2013 at 20:16
• "Addendum: I am not saying lighting is going to be 3% of your bill - I'm only making an example. You have to do the math - you have to figure out how much total power you're using (check electric bill) and then how much power your lights use (look at the bulbs and measure how long each one is left on each day) and that's your total % of energy for lighting. If that % is 15 then you can only reduce that 15%. You can cut your lighting costs in half, but half of 15% is only 7.5%." - that's pretty explicit don't you think? Commented Oct 11, 2013 at 20:39
• No, but it doesn't matter what I think, it matters what the OP perceives. I'm probably just dense, sorry. This isn't helping clarify things for anyone else, so let's just move on. Commented Oct 12, 2013 at 19:39

I don't think anyone is advertising that switching out a single bulb will save you loads of money, but when you consider the savings across your entire house, it does start to add up. Even if there was a \$0.50 savings per bulb per month (on average), my house probably has 60 bulbs, so that's \$30 a month or \$360 a year.

Regarding LED's, the incremental savings between a CFL and LED will be smaller than between an incandescent and a CFL. Lets say a common incandescent is 60w, and a comparable CFL is 15w - that's a savings of 45w per bulb. If a LED is 5w, then there is only a 10watt incremental savings between the two or 55w between an incandescent and LED.

The cost of the bulb versus bulb lifespan also plays a role. Incandescent are cheap, CFL's more expensive, and LED's most expensive, but their lifespans are also longer. What this means is that CFL's and LED's take several years before the cost of the bulb is paid off. Whether or not the savings in electricity offsets this really depends on the cost of electricity. In some regions, power is cheap and switching to LED is unlikely to ever save you money.

• This really doesn't explain why the cost savings of a 100w incandescent vs a 15w CFL left on for 24hrs over a period of a month only saves your \$5-6. If you think about it you don't leave all you light on 24/7. So the break-even factor is that if you replace your incandescent bulbs with CFL's and you see little difference in the total cost of energy, is their a better solution? Incandescent vs. CFL, is it really worth it? Your exposing yourself small amounts mercury which leak from a CFL over their lifetime plus high cost to install and low return on your bill. Commented Oct 10, 2013 at 17:18
• @LionelMorrison - plus CFLs are hazardous waste when disposed.
– mike
Commented Oct 10, 2013 at 17:23
• @Steve - if the savings is \$0.50 per month on a bulb (per your estimate), that's \$6-per savings per bulb per year. Since \$6 is more than I've ever spent on a CFL, my bulbs must be paying off within a several months, not several years. Either that, or the per-bulb savings is more line \$0.10 per month, which extrapolates to a \$6 per month lower electric bill for a 60-bulb residence.
– mike
Commented Oct 10, 2013 at 17:28
• The quote in the OP's question said \$5-6 a month per bulb which sounded crazy high to me ("100W bulb might cost about 5-6\$ more for that month than a 15W CFL"), so I just used 0.50 as a small value. Cost of bulbs depends on region, CFL's usually cost more than \$6 for me. Commented Oct 10, 2013 at 17:41
• ... for being on 24/7
– mike
Commented Oct 10, 2013 at 17:56

If power costs you 11.4 cents per kwh (and that's pretty close for a lot of people), then your annual cost for power is easy to figure: a dollar a watt. Per year.

Then divide by the fraction time that it's on, e.g. that 100W dusk-to-dawn barn light is on half the time, so \$50 a year. Easy peasy.

You go from a 100W incandescent to a 14W LED, that's \$86 saved if you ran continuously... but since you run 1/3 of the time, it's \$29 a year. Per bulb of course.

Let's say we have 2 bulbs connected in parallel

```    Volts   Amperes  Ohms   Watts
1   120     0.5      240    60
2   120     0.5      240    60
________________________________
T   120     1        120    120
kWh 0.12
```

Now we swap out one bulb with a 15W CFL

```    Volts   Amperes  Ohms   Watts
1   120     0.5      240    60
2   120     0.125    960    15
___________________________________
T   120     0.625    192    75
kWh 0.075
```

We'll see in this case, we've reduced our consumption by 37.5%. If we replace both bulbs, we'll save 75%!!!

```    Volts   Amperes  Ohms   Watts
1   120     0.125    960    15
2   120     0.125    960    15
___________________________________
T   120     0.25     480    30
kWh 0.03
```

On the packaging, we'll print in large type

# REDUCE ENERGY CONSUMPTION BY UP TO 75%!!!

But wait, that doesn't seem right. Can we really cut our electric bill by 75%, simply by replacing light bulbs? What if we have 10 things (maybe not all light bulbs) in the circuit?

```    Volts   Amperes  Ohms   Watts
1   120     0.5      240    60
2   120     0.5      240    60
3   120     0.5      240    60
4   120     0.5      240    60
5   120     0.5      240    60
6   120     0.5      240    60
7   120     0.5      240    60
8   120     0.5      240    60
9   120     0.5      240    60
10  120     0.5      240    60
_______________________________________
T   120     5        24     600
kWh 0.6
```

And we only replace one?

```    Volts   Amperes  Ohms   Watts
1   120     0.5      240    60
2   120     0.5      240    60
3   120     0.125    960    15
4   120     0.5      240    60
5   120     0.5      240    60
6   120     0.5      240    60
7   120     0.5      240    60
8   120     0.5      240    60
9   120     0.5      240    60
10  120     0.5      240    60
_______________________________________
T   120     4.625    25.95  555
kWh 0.555
```

That's only a 7.5% savings! What if we have hundreds of devices?

As The Evil Greebo says, you can only save a percentage of a percentage. If your lighting load is only a small percentage of your total load, switching to CFLs will only reduce the lighting percentage by a specific percentage.

NOTE: These values are for example purposes only, they do not take into account power factor or other real world variables. Don't be a nitpicker. If you'd like to have a discussion about this topic, please do so in chat

# Billing Methods

Another thing to consider, is the billing practices of your local utility.

## Block Billing

They may not be charging you based on your actual usage, but instead may be "block" billing you. They may, for example charge \$X.XX for the first x kWh, then \$X.XX for x - y kWh, then \$X.XX for each additional kWh over that. In this case you'd have to decrease your usage enough to move into the lower bracket, before you'd see a change at all.

## Budget Plans

Most utilities also offer what's known as a budget plan. This is where you pay the same amount each month, despite your actual usage. The budget amount is typically the average from previous years. In a plan like this you'll have a "balancing month", where you'll pay the difference between the budget amount and the actual usage. This amount can be lower or higher than the budget amount, depending on your usage.

## Fees, Taxes, and Other Charges

You'll also likely be responsible to pay some other fees, taxes, and other charges, which may be fixed prices even if you use nothing. For example. There may be a basic service charge, which is an amount due just for being connected to the grid. This amount is due even if you use 0 kWh. Then there are delivery charges, maintenance charges, because-we-can charges, and of course, you'll have to pay taxes on the whole lot of it.

• Another factor is heat generation of incandescent light bulbs. For example, during winters in northern Montana (subzero temperatures) I burned a 100W bulb 24/7 to keep an outdoor below-grade well pump from freezing. Switching to CFL/LED bulbs will have the added benefit of reducing summertime A/C needs (a further reduction in one's electric bill), it will also have the 'negative' effect of increasing heating costs in the winter. This applies to all heat-generating appliances, such as computer monitors and TVs.
– mike
Commented Oct 15, 2013 at 21:01

We had a home where the average electricity bill was \$250.00 per month. Then we switched all the light bulbs to LED's and our first new Bill with LED's was \$44.00 And that's no joke. But you have to switch them all out. These bulbs were 6W to 12 watts and the house cooled down as well, so the AC was used less. LED bulbs are 10% heat and 90% light. vs CFL's that are the complete opposite. So look it up.... Not all LED's are the same. Some won't last as long. They usually last 20-22 Years depending on Hour use. Look at all different types before you buy, and they are more expensive. Good luck

In my case, in September 2015, I replaced six 50 watt halogen light bulbs in the kitchen, with six 5 Watt LEDs. These lights are on for a good portion of the day; I would estimate at least 5 - 8 hours per day. For the months that followed my electricity consumption was reduced by about 10%. I couldn't attribute to anything other than changing those light bulbs. The reduction was compared from one month to the next and from the actual month to the year prior. I may have underestimated my energy consumption and it may have been much greater per day.

We have a stratified rate plan, so peak periods prices are double the non peak prices, plus there are delivery charges added to your bill based on your consumption. In short, I must have been consuming somewhere in the neighborhood of 3 kilowatt-hours per day, or 90 kilowatt-hours per billing cycle. At about 18 cents per kw hour, it means I saved about \$15 per month. I'm considering changing some of the other lights that we use to a great degree in the hopes that I will save more money.

It also depends on the kind of lamp and your usage pattern.

My home office is lit for up to 12 hours a day by a single bulb; that was a prime candidate for upgrading.

My living room is lit by a fixture talking 16 candelabra bulbs. With incandescent that's 640 Watts at full power, less of dimmed down to more usual levels. With LEDs it's more like 64 at full power, and 20 at normal brightness levels for that room. Small incandescent bulbs are especially inefficient, and again after good places to start this investment.

As others have said, 75% reduction of 4% of your total bill (compared to incandescent) is a 1% reduction in the bill. Not a lot. But multiplied by years of bulb life, it more than pays for the bulb. And you get the convenience of longer time between having to replace bulbs, plus the ability to feel you are doing something (admittedly minor) to address everything from global warming to the strategic hazard of being dependent on foreign energy producers. (I leave it to you to decide which arguments make sense to you, but there are plenty.)

Infrequently mentioned additional benefit: more efficient bulbs means I don't have to think about upgrading my 100A service; I've freed up power to be used elsewhere in the house.

I'll also note that dimmable LEDs work a whole lot better than dimmable CFLs, and these days may be cheaper. I'm actually slightly regretting my early investment in CFLs, since they will take years to wear out and give me an excuse to replace them with LEDs, and home automation will be a lot simpler with the newer tech.

Final point, re losing the incidental heating: true, but in most areas electric heat is the most expensive option. Burning more oil or gas does offset some of the savings, probably. But I believe you'll still come out ahead. And as noted that issue is balanced by reduced AC use in summer, if you're in a climate where air conditioning is used.

• I've also got a personal reason for trying to save wastts. I installed basic solar panels a few years ago, and I'm still looking forward to the first negative electric bill. I've gotten negative usage a few times but need to save another \$5 or so to account for the network connection fees. Replacing my 14-year-old fridge and 25-year old laundry machines would probably make a much larger difference, though. Commented Mar 6, 2016 at 3:18