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I asked Reliance Controls about a THP103 meter that I was having trouble with. Turns out that its 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 using) they replied with the following which I'm assuming isn't public knowledge because the average person don'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 turn off the lights when you leave the room. However, I work long hours and light is some what an 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 like 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's bulbs make any difference in terms of lowing costs to a noticeable degree?

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Which of your appliances are electric? such as an electric water heater. –  mike Oct 10 '13 at 17:31
    
Stove, fridge, freezer, washer, dryer but not the Water heater. That is propane. –  Lionel Morrison Oct 10 '13 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 Oct 10 '13 at 17:49
    
Most LED bulbs I have seen only reduce the wattage consumption for a 60W equivalent by ~25W (e.g. I have a 23W CFL and an 11W LED bulb -> 22W difference) and ~10W for a 40W equivalent (e.g. I have a 14W CFL and an 8W LED bulb -> 6W difference) . To put it simply, the cost savings really is not there if you do not think switching from incandescent lights to CFLs is saves money (e.g. 60W incandescent to 23W CFL -> 37W difference, and 40W incandescent to 14W CFL -> 26W difference) since the wattage consumption difference going from CFL to LED is even smaller than incandescent to CFL. –  user14416 Oct 10 '13 at 19:03
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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. –  BlueRaja - Danny Pflughoeft Oct 10 '13 at 19:24

4 Answers 4

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 = 24,000W
  • Lights on 8 hrs a day = 800W
  • Total daily usage, 24,800W

In that scenario your lights represent 800/24800 or 3% of your daily electrical consumption.

If you replace your light with a 15w bulb you've dropped from 24,800 to 24,120/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%.

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FWIW, my fullsize fridge draws less than 200W when running and does not run 24/7 –  mike Oct 10 '13 at 18:01
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Yeah, so? My example fridge has a bad door seal. I'm making A POINT here! ;) –  The Evil Greebo Oct 10 '13 at 18:02
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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 Oct 10 '13 at 18:04
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@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. –  The Evil Greebo Oct 10 '13 at 18:10
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@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 Oct 10 '13 at 21:22

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.

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"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. –  The Evil Greebo Oct 11 '13 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. –  bcworkz Oct 11 '13 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? –  The Evil Greebo Oct 11 '13 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. –  bcworkz Oct 12 '13 at 19:39

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.

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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 Oct 15 '13 at 21:01

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.

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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. –  Lionel Morrison Oct 10 '13 at 17:18
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@LionelMorrison - plus CFLs are hazardous waste when disposed. –  mike Oct 10 '13 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 Oct 10 '13 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. –  Steven Oct 10 '13 at 17:41
    
... for being on 24/7 –  mike Oct 10 '13 at 17:56

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