Economics of CFL

CFL- Compact Fluorescent Light Bulb. What is it? Basically it’s a fluorescent light, but much smaller and it includes the ballast for starting the bulb.

All the hub-bub about these new lights is totally deserved I think. They save energy and last longer. For example, you probably use mostly 40, 60 and 100 watt lights in your house right? Some burn for hours at a time (like the front portch). What if you could use 14, 20 and 32 watt bulbs respectivly and get the same amount of light? Think it would save you some money on your power bill?

The truth is that many folks are turned off by one thing- the initial investment of the bulb. I just went out and bought 9 CFL lights for my house. It cost me $82. Sound like a lot? Well, it is, but only up front. Over time they will save me money and not just from the power they use.

Did you know that in incandescent lights 90% of the power they use turns into heat? That means that only 10% of the energy is light. Why waste 90% of your lighting cost heating your house??? The CFLs will save you money on cooling because they’re generating less heat.

Most CFLs also put out more lumens (overall light) than standard lights. I don’t have the numbers off hand, but the quality of light in our bathroom where we had 4 60 watt bulbs was very yellow. We put in 4 16 watt decorative CFLs and not only is the bathroom brighter, but it’s a white light.

How long do CFLs last? A LONG time. Look at this table:

Hours 7,500 to 10,000

This table is typical for a 60 watt bulb. You’d need to replace that incandescent light 13 times to get the same life as 1 CFL. Keep in mind these numbers are optimistic and will vary. But even if you cut them in half, CFL is still on top.

Lets do some math. There is definitly a break even point for cost vs. savings. We’re not talking about saving hundreds of dollars, maybe just a few dollars a month plus the hassel of changing lights. Personally, I like keeping money out of the power companies hands…As for break even points- the more you use the CFL the more savings you’ll see. If you only use a light one hour a day, over the course of the year, you won’t see a savings…

For this VERY simplified example, we’ll use my front portch light. It runs about 12 hours a day and is on a light sensor. Power costs in my area are about 7.9 cents a KWh. (That’s adding the fuel and energy costs together.) So running it 12 hours a day, 364 days a year costs about $11.04 per year to run or .0303 cents a day. If I used a standard 100 watt bulb, it would cost $34.51 per year or .0948 cents a day. Ok, so there seems to be an energy savings. But that’s not the whole story. We still had to pay for the bulb. So, at about .37 cents for the standard bulb and $8 for the CFL we have some savings shifts. Keep in mind that you’ll need about 6 of the standard bulbs over the year. So, lets adjust the costs of the bulbs- $2.22 for the standard bulbs and $8 for the CFL. Next we’ll add the bulb cost to the energy costs and come up with $36.73 for the standard bulb and $19.04 for the CFL bulb. The savings by using the CFL turns out to be $17.69. Not too bad.

Now lets look at the bigger picture. Below is a table of more detailed info. Because of my kids, many of our lights run much longer than necessary. Because of this, the savings goes up. Basically, the more you use the lights, the more the savings. I figured this based on 10 lights (5 in the dining area, 4 in the bathroom and at least one in the kids room).

Incandescent Lights CFL
# of lights 10 10
Watts per light 60 16
Watts per hour 600 160
Operation Hours per day 6 6
Watts per day 3,600 960
Watts per 30 day month 108,000 28,800
KW per year 1,310 349
Power Cost to Operate Per Year $103.52 $27.61
0.2844 0.0758
Expected Hourly Life Per Unit 750 10,000
Cost Per Unit $0.37 $8.00
Expected # of Days of Operation 125 1,667
Number of incandescen lights needed to = 1 CFl 13 1
Total # of incandescent lights needed to = # of CFLs 133 10
Cost of light bulbs $49.33 $80.00
Total Cost Per Year $152.85 $107.61
Yearly Savings $45.25
Monthly Savings $3.77

NOTES ON TABLE- The table assumes that all the lights run for the same amount of time per day, every day all year long and is based on a 364 day year. The Power Cost to Operate Per Year is for all the bulbs combined. The Expected # of Days of Operation is for one bulb (and because we are assuming that they all run the same amount of time per day this should be the same for all of them…)

All of my examples up to this point have been centered around the cost savings over a one year period based on a certain amount of usage. The fact is that CFLs last much longer than that. If you ran one 24/7 it would last over 400 days, use it less and it lasts even longer!! So lets look at the same example as above not over a year, but over the 10,000 some odd hours that the light really lasts (or should anyway…).

Incandescent Lights CFL
# of lights 10 10
Watts per light 60 16
Operation Hours per day 6 6
Cost to operate for life of bulb $474.00 $126.40
Expected Hourly Life Per Unit 750 10,000
Cost Per Unit $0.37 $8.00
Expected # of Days of Operation 125 1,667
Number of incandescent lights needed to = 1 CFL 13 1
Total # of incandescent lights needed to = # of CFLs 133 10
Cost of light bulbs $49.33 $80.00
Total Cost per 10,000 hours $523.33 $206.40
Savings $316.93

You’ll notice here that the CFL should last around 1,667 days at 6 hours usage per day. Let see that’s about 4.5 years…and over that amount of time, you’d save $316.93.

If you’re trying to prove my math wrong, please try. Keep in mind that these two examples are based on two different methods, one on a years time frame and one strictly on hours. The cost differences you may see are because of this. For example, to run a CFL for 10,000 hours the total cost of the bulb and power is about $20.64. If you look at the cost of running a CFL for just one year plus the bulb cost it’s going to depend on the total number of hours you use it. If the hours used is 6 per day, the cost to use the CFL over a 364 day year is $19.04. Keep that in mind when you write me to tell me I can’t add….

Hopefully you can see that CFL lights do offer some savings, not just monetary. I know the up front cost is much higher (especially if you get the decorative or dimmable CFLs). But there are so many other things to consider. Most importantly you’ve got the numbers now so that you can decide what you want to do.

UPDATE- I did a cost justification write up for my former employer to see if replacing 73 incandescent lights that run 24 hours a day would produce savings they were willing to invest in….Here’s what I found out:

Incandescent Lights CFL
# of lights 73 73
Watts per light 100 27
Operation Hours per day 24 24
Watts Per Dat 175,200 47,304
Watts per 30 Day Month 5,256,000 1,419,120
KW per year 63,773 17,219
Energy Cost Per Year $3,75112 $1,012.80
Expected Hourly Life of Unit 750 10,000
Replacement bulbs needed 12 0.88
Capital Cost Per Unit $0.40 $8.99
Capital Cost of bulbs for 1 year $4.67 $7.88
Total Cost Per Year $4,092.17 $1,587.69
Savings Yearly $2,504.48

For a small business this stuff adds up! Hope you learned a little!


Author: Helicopter Jeff

I'm a vinyl decal cutting and designing, Astrophotography and general photography capturing, RC helicopter/quad copter pilot, Arduino and Raspberry Pi hardware/software developer, network, scripting and troubleshooting ninja living in the metro NY area. I am passionate about my hobbies so much I do them for a living. There's nothing better than getting paid to do what you love.

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