Lighting Cost Comparison - Incandescent vs. CFL

***Update - 10/4/09 - I have an improving lighting cost comparison that includes a lighting calculator and includes a residential LED bulb.  See the incandescent, CFL, and LED lighting cost comparison and calculator.

In the last few months I've heard this statement twice: "I want to conserve energy. I plan on changing out my incandescent bulbs to CFLs as soon as they burn out."

While thinking of CFLs is a great start, there is no need to wait until your old bulbs burn out.  If you do a life-cycle analysis (which I have done below) it makes much more sense to replace the incandescent bulbs immediately!  This is not just from a "save the Earth" perspective, but especially a cost savings one.

Based on the cost of electricity at .09 cents/kwh, a regular old 60 watt light bulb would cost you $10.80 over its 2,000 hr life.  The 14 watt CFL equivalent's electricity cost would only be $2.34 over the same 2,000 hrs (plus the CFL will last another 4,000 hrs after that)!   The only way it would not make sense for you to immediately change that old bulb is if the CFL cost  $8.46 or more, which I can assure you they don't ( I get mine for around $1.50 a pop).  So what are you waiting for?

The figure below displays 3 different scenarios for a 10-year lighting analysis.  The light is assumed to stay on for 4 hours a day, 365 days/year, for 10 years.  The first case is all incandescent, the second case is all CFL, and the third case is you replace the incandescent after it burns out, and use CFLs after that.  As you can see, immediately replacing the regular bulbs with CFLs provides the best payback!

-click on the thumbnail below, then move it around the screen if necessary


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Im homesschooled and this seems like a reliable investment to get Solar lights. Currently im doing a project with my brother were we have to design a blind that captures light and is able to use it later in the day. Does this seem liuke a good idea? Any ideas would be great.
ckmapawatt's picture
It's an interesting idea. how do you plan on capturing the light? You can use solar pv cells on the blind, store the electricity in a battery and then use that electricity in lights at night.
I used a amp/watt tester on CFL bulbs, a 13W used about 59 watts, and an 23W buld used about 120 watts. does anyone test or regulate this, surely someone has tested this bulbs for actural useage Watt (excuse the pun) am I missing
Greetings from open4energy A most informative discussion and excellent points being made by all. I live in a small two bedroom apartment and recently replaced all the old incandescent bulbs with latest version Energy Star approved CFL bulbs. I have my opinions on what is best to do, but rather than express them I decided to monitor the energy profiles, before and after, using a Watt-up Smart Circuit 20. Here is the graph, it compares the two sets of light bulbs, each set being turned on in the same sequence, with 15 seconds between them. The theoretical saving from the bulbs is a little under 75% if I adjust for the bathroom fan which remained unchanged. For those needing exact numbers, the peak load for the incandescent bulbs was 819.7 Watts with Power factor of 99% - while the load for the new CFL's was 230.6 Watts with Power factor of 79% I then wondered how this played out in real life. I did a second test, monitoring the actual living energy use on our bedroom/office/bathroom circuit for two days, once with the original bulbs and then again with the new CFL bulbs. Here is the graph of the four days of data, again monitored using the Wattsup Smart Circuit 20 Do note that this includes the energy used by my computer in the home office. Energy use in the first two days was 4657.6 Watt Hours, and in the second two days was 2400.3 Watt Hours, a reduction of 48.46% And much to my surprise, the Power Factor for the CFL two days was above 80% - I believe that the laptop computer with its mechanical reactive power was creating some compensation on the circuit? And if the energy data is "boring" the graphs provide way too accurate a record of when I worked on the computer, and when someone needed the bathroom in the night ......
Thanks for the link Janice, RE "insulation needs to be upgraded, ...Once these things are done, the CFL conversion will save energy" Actually as I say on my link with references, once insulation is upgraded the relative benefit of light bulb heat increases - not decreases - as heat is not escaping through the ceiling etc (remember that room heat substantially rises and comes back down from the ceiling) Also see bans in low emission states There are of course many factors apart from heat as to why cfls don't save energy/money I have recently extensively updated re lifespan, brightness and power factor for example see
Hi again there Chris, To summarize a bit and focus more on the cost related issues, like you said No doubt CFLs can save energy, but not as much as supposed. To begin with the simple usage factors: Lost, broken or malfunctioning expensive bulbs cost more to replace than cheap ones. Meanwhile, the "expensive to buy but cheap to use" concept tends to lose out, -- in rarely used lamps around the house -- in short stay situations, vacations, second homes etc Brightness problem of CFLs: Supposed equivalents are not actually equivalent in brightness, so higher energy using CFLs needed for adequate brightness. See recent testing of CFL brightness versus ordinary bulbs: More, with other links: CFL Lifespan is lab tested in 3 hour cycles. That does not correspond to real life usage and numerous tests have shown real life type on-off switching reducing lifespan. Leaving lights on of course also uses up energy, as does the switch-on power surge with CFLs Also, CFLs get dimmer with age, effectively reducing lifespan Power factor: Few people know that CFLs typically have a power factor of 0.5 - that means that power stations use up twice as much power than what the CFL rating shows. This has to do with current and voltage phase differences set up when CFLs are used. Although consumers do not see this on their meters, they will of course have to pay for it on their bills. This is explained with official links including to US Dept of Energy here: Heat benefit from using ordinary incandescent light bulbs A little bulb near the ceiling may not seem like much, but room heat substantially rises to the ceiling (convection) and spreads downwards from there. As shown via the above link with American and Canadian research references, half of more of the supposed switch savings are negated in temperate climates. <b>Effect on Electricity Bills</b> Inasmuch that energy use <b>does fall</b> with light bulb and other proposed product efficiency bans, electricity companies make less money, and they’ll simply raise the electricity bills to compensate (not least in USA, power companies often have their own grids with little supply competition) Energy regulators can hardly deny any such cost covering exercise… One might add that as Scottish and Cambridge university research shows (as referenced on the website) energy efficient products effectively mean cheaper energy so people just use the appliances more, leave them on etc. With CFL lighting that is actually advised anyway (due tom on-off switching reducing lifespan, but of course leaving them on as said in turn uses up energy... OK thanks again for a nicely put together site. Learning something every time I use it.
An extensive study was recently published in the July/August 2009 Home Energy Magazine. It closely examines the effects of the amount of heating load offset by the use of incandescents. It looks at heating degree days and length of season for many US and Canadian cities and also considers types of heating systems and how insulation levels, equipment condition and efficiency factor into the outcome. As summarized: "If [after examining data] there is any question as to whether a CFL conversion will save energy, it means that either the heating system needs to be repaired or replaced, or the insulation needs to be upgraded, or both. Once these things are done, the CFL conversion will save energy. If the climate is so mild that heating and insulation upgrades are not cost effective, a CFL conversion will almost certainly save energy even without them." Go to to read the full article.
Thanks for the great comment!
I believe you forget some factors, including life cycle transport from China, recycling etc, see <a href="" title="" rel="nofollow"></a> onwards also full facts re heating see <a href="" title="" rel="nofollow"></a> In general while consumers may benefit from energy refficiency, it's hardly for governments to decide: the energy supply is not a problem, and emissions can be dealt with, including funding, as also described on the website
Peter, thanks for the comment, but I was merely doing the cost analysis from a consumer standpoint, not a life-cycle analysis from an environmental standpoint. It all depends on what the consumer cares most about. If it is just saving money then the CFL is the hands down winner. If it just saving the environment, then more analysis needs to be done to look at shipping costs, how the product is manufactured, how it is disposed of, packaging, etc...


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