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The Brightest Bulb

I was talking to someone who was considering using the VOIP (Voice Over IP) offered by their cable company. She was concerned about how much the modem would cost her to run. I came to realize that she was on a tight budget and was wondering how much it would add to her electric bill.
I didn’t know off hand how much power a modem draws so I started to think about a 100W bulb, and figured we can scale from there. If a bulb were left on 24/7, it would use about 72KWH of power in a month as there are 720 hours in a 30 day month. At her rate of 15 cent per KWH, this one 100W bulb would cost $10.80 to run full time each month. It turns out a modem is 10W or less, so it’ll take about $1/mo to run.
This exercise got me thinking. I bought a device a few months back to help me add up the current I use in my basement as I was wiring it room by room. It’s called Kill A Watt and available at Home Depot or on line.

The first thing I did was to find a power supply plugged into an outlet in my office with nothing attached. 4 watts! Now, I can afford the 40 cents per month, but how foolish is this, there’s nothing even plugged in, it powered a hard drive that’s now in a closet but I forgot to unplug the supply till now. Next, I checked how much power one of my old Macs was drawing. I was glad I use it remotely, no monitor, saving that power. But I found it uses 180W. About $19 per month. I need to rethink whether it’s worth it to keep this guy running.

Last, I’ve been replacing the incandescent bulbs with CFL (Compact Fluorescent Light bulb). Most rooms in our house have 4-6 in-ceiling cans that hold a 65W spotlight type bulb. The CFL replacement is 15W and puts out the same amount of light. So, anytime we are in a lit room, we’re saving 200W of power. Of course, during the day, it’s good to pull the shades/blinds and use natural light, but when we need to turn them on, it’s less power and less heat generated. How many power bricks do you have plugged in that are just keeping warm and burning your money? Have you gone to CFLs yet?


  • Brad October 1, 2010, 11:19 am

    Three years ago I switched to all CFL’s in my kitchen can lights. They are enclosed in a bulb to look like the others. I went with a mail-order higher-quality bulb. There were 7 can lights in my kitchen. The bulbs were not cheap, $12 each by buying in quantity. So far, in the past two years, I have replaced the bulbs a total of 14 times. 12 under warranty. 2 I had to eat the cost. The company says it’s due to the electronics of the CFL.

    So the problem is when your $12 bulbs only last a year or so. The burn life on the box assumes an upright CFL with no cycling in a perfect environment. (So you can’t turn it on and off to achieve the results they say).

    In my reading lamp, I bought a $10,150-Watt CFL last month. Last night it wouldn’t turn on. I gave up and it turned itself on 10 seconds later. Go figure. As far as I am concerned, a light bulb that doesn’t work 100% of the time isn’t worth a dime. Ironically, the traditional light bulbs cost about that.

    Also, you must take the total energy, not just the running energy. CFL’s take more juice to power up I believe, like other fluorescents. I think you’d have to take a normal full day’s use to measure total electricity used, and that would include measuring times that it is turned on and off.

    I’m all for CFL’s, but I don’t think I’ve experienced a dime of cost savings since switching. And we haven’t even discussed the mercury issues and what to do with these bulbs. If I have to drive somewhere or pay to have them shipped somewhere for disposal, then those are costs as well to consider.

    Basically, don’t trust everything a CFL manufacturer tells you.

  • JOE October 1, 2010, 1:34 pm

    Recently, our utility companies have offered instant rebates. The bulbs are 90 cents at the register. At a 50W reduction, a bulb saves me 15 cents every 20 hrs of use. After 120, they pay for themselves. The break even for most rooms is barely a month, maybe two. (If one is home all day, and using the light 10 hrs per day, we are talking less than a 2 week break-even.
    Brad – I agree 100% that needing a year or more to break even and having faulty bulbs is a money loser. I’ll admit that years ago I gave up as well. The bulb’s light was yellow, they were expensive, and they didn’t last. The newer series seem to have eliminated these issues. If my wife isn’t complaining about the light color, I’m doing well.

  • Penny Frugalista October 1, 2010, 11:06 pm

    We’ve been slowly switching over from incandescent to CFL bulbs throughout our home as the old ones blow out. We even use the CFLs in our porch lights. I’ve had no issues with faulty bulbs nor the color. However, I do find the “bright white” bulbs, which I prefer, cost more than the “soft white” variety.

  • Roshawn @ Watson Inc October 2, 2010, 8:33 pm

    This is an area where my wife and I are quite lax. I seriously have no idea of the cost differential but suspect that we are probably not efficient. That said, I don’t think we are particularly wasteful, but certainly not streamlined either. I’ll have to give this some more thought and discussion.

  • JOE October 2, 2010, 9:08 pm

    I’d always told Jane and Jane 2.0 to turn off the lights when they leave a room, but it wasn’t until I did the math that I realized how much it was costing us. It really adds up. (Not to mention the heat they create in the summer, in the winter it didn’t matter, but when the AC is running…)

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