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Does it pay?

When I was a kid, my parents would follow us around the house shutting off lights and mumbling something about money growing on trees. Now that I am a parent, I find myself in that same role. While I have no aspirations of finding that tree money grows on, I have started to wonder if:

  1. My panic at seeing all the lights on is warranted.
  2. Keeping all these lights running is really costing me that much money.
  3. Since I have replaced my burned out lights with CFL (compact fluorescents), is this taking the edge off?

I started crunching the numbers, and this is what i found.

Determining usage


In thinking about leaving lights running, I started thinking about several other things that run in my house. Servers, refrigerators, wall wart charges, and the like. Unfortunately, in order to test those devices, I need another piece of gear. For those technically oriented, I thought about rigging my meter so that I can put it in series with any of my gadgets, but I found that my meter does not read true RMS.
It turns out that the Kill A Watt EZ Electricity Usage Monitor does just this, but without the dangerous wiring. It’s on my wishlist , so if anyone decides to buy it for me, I promise to test everything in my house, and post the results for all to see.
The gist is, you plug your item into this gizmo, and it calculates how much power is used. This can easily be converted to dollars.

How the electric company figures your bill

The electric company pretty much has a gizmo just like this (but more rugged, and more thoroughly calibrated.) Your bill is based on killowatt hours. This is wattage used by an appliance multiplied by the time that wattage is used. For example:

  • A 100 watt bulb, running for ten hours, uses 100 watts x 10 hours / 1000w/kw = 1 killowatt-hour.
  • If you look at your electric bill, you will see that they tell you how much you pay per killowatt-hour. First Energy charges me 7.36 cents. So the cost to me to run that 100 watt bulb is 7.36 cents.

Okay, so that number doesn’t seem to warrant too much freaking out.

Checking out my house

I did a quick check on my house, to see what lights get left on most often. Those are: The living room, the kitchen, basement. Just to be fair, I gave decided to estimate the hours that the lights were on when no one was using them. That time was about two hours per day.
This is how it worked out:

RoomTotal WattageCost Per Month
Living Room100W + 100W + 60W = 260W260W * 2hours * 30days * .0736 = $1.15
Kitchen60W total60W * 2hours * 30days * .0736 = 26 cents
Basement (all CFL)42w + 42w + 20w = 104w104w * 2hours * 30days * .0736 = 46 cents

So, this tells me that if I fret and run around the house turning off lights, I stand to save less than two bucks. If I relax about the lights, I get to settle down a bit, and it only costs me two bucks.

Replacing my lights with CFLs

Compact Flourescent Lights are dropping in price every day. Now, whenever a bulb burns out, I replace it with a CFL. I decided to do a little calculating to see how much this transition saved me over the course of a month.

My house is small. We only have about three rooms being lit at once, and then, only for an average of about 5 hours per day. That number will rise in the winter, but not much. So, let’s see how much it costs me to light my house, assuming those numbers, as opposed to incandescent lighting.

The trick with CFLs is they give you two wattage ratings. One, the wattage rating for the power they use, and the other, the equivalent incandescent wattage. In each room, we have two 26 watt bulbs (100 incandescent watts each) and one 15 watt (60 incandescent watts) bulb. This gives me 260 incandescent watts for the cost of 67 watts.

So, here’s how much it costs to light my house either way, assuming 3 rooms, 260 incandescent watts, 5 hours/day, and 30 days:

LightingKillowat-hours / monthCost/Month
Incandescent3 * 260W * 5hours * 30days = 117kwH$8.61
CFL3 * 67w * 5hours * 30 days = 30.15kwH2.21

So, the total savings for each month is $6.41.

Now, if you are in a similar situation, but have not made the transition to CFL yet, you can assume the lights will cost you about $3.20 each. In this case, each month, the cost of two bulbs will be saved. So, in my case, I recouped the cost of the bulbs in five months.

Is it worth it?

From what I understand, all bulbs will be switching to CFL soon, so we will not have a choice. But yes, it seems to be worth it. In order to get an equivalent light, you spend about a quarter of the cost in electricity.

As for shutting off every light in the house as and following people around to do so, no, it’s not worth it. Now that the usage has dropped by three fourths, it is really not worth it.

Now, my electric bill is still about $100 dollars a month. This might justify me buying the Kill A Watt EZ Electricity Usage Monitor to track down the culprit, but at this point, it’s not a good idea for me to be spending money. I have a suspicion it’s the cable box, the tivo, the tv, or some major appliance.
So, remember that wish list , and if I get one, I promise to teach you all how to find what is killing your electric bill.