Question Re Use of Compact Fluorescent Lamps (CFLs)

Turning a CFL on and off frequently can shorten its life. To take full advantage of the energy savings and long life of ENERGY STAR qualified CFLs, it is best to use them in light fixtures you use the most and are on for at least 15 minutes at a time. Good locations include outdoor light fixtures, indoor fixtures in the living room, family room, kitchen, bedroom, recreation room, etc. This is not to say you should leave your lights on all day if you use ENERGY STAR qualified CFLs. It is still a good habit to turn the lights off when you leave the room for an extended period of time. You may also have heard that CFLs use a lot of energy when turning on and off. While there is a brief surge in energy use when a CFL is turned on, with today's starting technology, that surge usually lasts about a tenth of a second and consumes about as much energy as five seconds of normal operation. So, even when turned on and off frequently, a CFL uses less energy than its incandescent equivalent. But because turning a CFL on and off more frequently can shorten its life and CFLs are more expensive than incandescents, we recommend consumers use CFLs in applications where they are on for at least fifteen minutes. http://energystar.custhelp.com/cgi-bin/energystar.cfg/php/enduser/std_adp.ph p?p_faqid=2569

There was a whole show about this question on Discovery Channel Mythbuster. The result was a "busted" myth. It's better to turn lights on and off. Here is the result and link: http://kwc.org/mythbusters/2006/12/episode_69_22000_foot_fall_lig.html Lights On or Off Myth: You save on energy bills by leaving lights on. Some people believe that the energy to turn on lights exceeds savings of turning lights off. They talked to Mark Reisfelt, manager of the Independent Electric Supply where they purchased their light bulbs. He felt that it was best to turn the lights off. To test the myth, they needed to measure energy usage during startup, maintenance (steady state), and shutdown. For steady state energy consumption, they turned on several different types of bulbs for 60 minutes and measured their consumption using a Kill A Watt : * Incandescent 90 Wh * Compact Fluorescent (CFL): 10 Wh * Halogen: 70 Wh * Metal halide 60 Wh * LED: 1 Wh * Fluorescent: 10 Wh For startup energy consumption, Grant hooked up an inductive current loop to a computer and measured the amount of energy used when the turned on the bulbs. With an inductive current loop, you run a wire through the center, which induces a current in the loop. This current is then measured by a digital sampling oscilloscope. Based on the amount of energy consumed turning on the bulb, they were able calculated how long the bulb would have to be turned off in order to make it worth the energy savings, i.e. "It's best to turn off the bulb if you are leaving the room for": *Incandescent: 0.36 seconds *CFL: 0.015 seconds *Halogen: .51 seconds *LED: 1.28 seconds *Fluorescent: 23.3 seconds In other words, its almost always best to turn the bulb off. Even the 23 seconds for the fluorescent lights isn't very long, and the rest of the times are pretty much blinks of an eye. Bulb Longevity They tested one final element of this myth: frequently turning lights on and off decreases their life span, thus leading to greater costs. Grant setup a timer and relay to turn the bulbs on and off repeatedly every 2 minutes. After six weeks, only the LED bulb was still working. Based on this test, they extrapolated that it would take five years of ordinary usage to cause the bulbs to burn out. * busted * Side-note: 105-year bulb Grant and Kari visited the Livermore/Pleasanton Fire Department to view their light bulb that has been burning for 105 years. It has a carbon filament that is much thicker than modern bulbs and also burns much cooler/darker. You can check on the light using the bulb's webcam.

Hi Helen,

If the room is to be unoccupied for more than about 10 or 15 minutes the CFL should be switched off. Frequent switching of CFLs has the effect of slightly reducing their life. However, if you add the time they are switched off to the slightly reduced operating life due to switching them off, the total calendar life is greater than if they are left on all day.

Cheers
John

John Osborne

Renewables, Sustainability Victoria
T: 03 8626 8783
F: 03 9663 1007
Level 28, Urban Workshop,
50 Lonsdale Street, Melbourne 3000
www.sustainability.vic.gov.au

In fact I would go further than that and switch them off every time I leave the room for more than 5 minutes. The warm up time myth is a legacy from long ago (5 years or more :) when they could take 30 seconds or so to come to full brightness. The other myth is that they use more energy to switch on than they do to run. This is sort of true but think about this. Imagine it takes 100 times more power to turn on and that it takes a whole second to turn on. That means it would use a hundred seconds of energy to turn on! But that's less than two minutes! In practice modern CFL's turn on in less than one tenth of a second and take about 6 to 10 times more power to turn on so they use less than one second of energy to turn on.

Cheers
MOC 

the mythbusters piece showed that it's basically better to turn lights off when you leave the room, period, even considering the reduction in bulb life for CFLs.

Hey Helen, I just watched an episode of Mythbusters in which they addressed this very issue. They tested all forms of bulbs from traditional to CFLs to LEDs. Regardless of the type of light, all used only enough energy during "start up" that you would have to leave the room and return before you could blink to make it more cost effective to leave it on. Even with the reduced life span from turning them on and off, the cost of electricity saved far surpassed the cost of replacing the bulb when it went out. They had tested the on off capacity and found that switching them on and off every 2 minutes for 6 weeks would burn them all out (except the LED) but that worked out to over 10,000 flicks, adding up to several years of regular usage. Bottom line. it's always better to switch off the light! (Unless you move faster than you blink! :-))

Cheers,
Danny Lewis <><

Education Coordinator
Raven Recycling Society
Whitehorse, Yukon
(867)667-7269 ext. 23

This is an old thread, but I think you may have reached a misleading conclusion.

For starters, I question the Mythbusters comparison of a 10-watt CF bulb to a 90-watt incandescent bulb. The most optimistic manufacturer's claim I found to substitute for a 90-watt incandescent is a 23-watt CF bulb. This is 2.3 times as much energy usage as Mythbusters alleges. (In my opinion, Mythbusters values sensationalism over accuracy; they are a TV show, not a scientific laboratory.)

I also note a subtle but crucial factor--you describe saving *energy*, while most people are interested in saving *money*. The key difference is the cost of replacement light bulbs. The Lighting Research Center at Rensselaer Polytechnic Institute found that the lifespan of a CF bulb is profoundly impacted by how often it is turned on and off. In their tests, a CF bulb on a 5-minute switch cycle lasts only 15% as long as its rated hours. So if you typically use a CF bulb for 5 minutes at a time, you'll use seven times as many bulbs as the package claims--and that adds up to a lot of money! LRC used 440 bulbs in their test, under laboratory conditions described in the report. As you describe it, Mythbusters seems to have used a sample size of just 1 CF bulb--apparently without even a control CF bulb for comparison. From my knowledge of statistics, it's impossible to extrapolate a comparison with an uncontrolled sample size of 1, but Mythbusters somehow does so to arrive at their sensational "busted" conclusion.

So while you will obviously save energy by turning off a compact fluorescent bulb when you leave the room, it may cost you money! And I'm not sure Mythbusters is doing anything but generating more myths.

I suggest you consult the Lighting Research Center's detailed testing results here: http://www.lrc.rpi.edu/nlpip/publicationDetails.asp?id=114&type=1 -- see "Specifier Reports: Screwbase Compact Fluorescent Lamp Products", a 79-page free PDF listing their extensive lab results.

Best regards,

-Tom Jones

Tom Jones
United States