One of the easiest ways for you to save energy is to install energy efficient fluorescent lights in your home. Fluorescent lights can save you up to 75% of the electricity used by a traditional incandescent light bulb. They also last up to ten times longer than incandescent bulbs. A fluorescent light bulb usually pays for itself within a year if used at least two hours per day.

Compact fluorescent lights or CFLs are the most common energy efficient fluorescent lights in homes, because you can use them as efficient replacements for regular incandescent bulbs. CFL bulbs consist of a looped or spiraled fluorescent tube. In the case of a spiral tube, the spiral is either covered by a plastic dome (to mimic the appearance of an incandescent bulb) or exposed. Exposed spiral CFLs are often referred to as energy saving spiral bulbs.

Tube fluorescents are commonly used in commercial buildings, but also in the home, for example under upper kitchen cabinets to light up a counter, or in the workshop or garage.

Circular fluorescent bulbs are circular tubes with a diameter between 6 and 9 inches that can replace an incandescent bulb in an open ceiling fixture.

Many energy efficient fluorescent bulb configurations can be replaced with even more efficient LED house lights. But since LEDs cost a lot more than energy efficient fluorescent bulbs, my personal opinion is that it’s more cost effective and energy efficient to spend your money on replacing a larger number of fixtures with energy efficient fluorescent lights, rather than a much smaller number of fixtures with costly LED house lights. If you want you can compute the savings yourself with my CFL savings calculator and LED savings calculator.

On this page I’ll answer the following general questions on energy efficient fluorescent bulbs:

If you don’t find your question answered here, please see our Efficiency Questions section, where you can search for energy efficiency questions we’ve already answered, or ask your own.

Are all fluorescent lights energy efficient?

Fluorescent lights are pretty much always more efficient than incandescent lights or halogen lights. When we measure the energy efficiency of lights we need to account for the total energy input and the useful visible spectrum light output.

In theory, a light bulb could be constructed that is 100% efficient, but the most efficient lights of any type in existence today are only 27% efficient, based on overall luminous efficiency (source: While most incandescent lights are between 2 and 2.5% efficient, energy efficient fluorescent lights are between 6.5 and 15% efficient, with a typical CFL being three to four times more efficient than an incandescent bulb providing the same light output.

Fluorescent lights are also more energy efficient in terms of total life cycle cost – the total energy used to manufacture and power the bulb over its useful lifetime. Energy efficient fluorescent lights take more energy to manufacture than incandescent light bulbs, but because they last 8-10 times longer and use far less energy while running, their overall energy use (manufacturing energy + operational energy) is far lower.

There are three situations in which fluorescent lights can be less efficient than incandescent bulbs:

  • If a bright incandescent light is replaced with an energy efficient fluorescent light that provides less light, you may not notice a light left on and it may stay on much longer. This happened to us in a hotel in Costa Rica, where the bathroom bulb (a single, 13-watt CFL) was so dim we didn’t notice it was on, and it got left on all night. Don’t go too dim!
  • If an incandescent light is replaced with an energy efficient fluorescent light but the light is almost never used, the energy used to manufacture the bulb may never be recaptured in overall energy savings. For example, I turn on the light in my furnace room about five times a year, for 2-3 minutes each time. At that rate it would probably be decades or centuries before the total energy cost of an incandescent would exceed the total energy cost of a CFL.
  • If you start leaving the light on because you assume it is energy efficient, you could use more energy. This is one aspect of a phenomenon known as the Jevons paradox, where increased efficiency leads to increased consumption of a resource instead of decreased consumption. I have seen many people who used to turn lights off religiously whenever they left a room, but who stop turning off the lights when they upgraded to CFLs.

How do fluorescent lights work?

Energy efficient fluorescent lights operate by a two-stage process. First, electrical current regulated by a ballast is passed through a gas containing mercury vapor. The current excites the mercury vapor, which causes the mercury vapor to emit photons in the ultraviolet range of the spectrum. Since ultraviolet light is not part of the visible spectrum, energy efficient fluorescent lights are coated with a phosphor that absorbs the ultraviolet light, and that then fluoresces, or emits photons of visible light. Almost all the ultraviolet light emitted by the mercury vapor is captured and converted to visible light by the phosphor; the small amount of ultraviolet light not converted to visible spectrum light poses no health hazard to people exposed to the light. (Natural sunlight includes ultraviolet radiation, which is what gives us suntans or sunburns!)

The ballast is a current-regulating device that controls the amount of electrical current passing through the mercury vapor, so that it can provide a constant amount of light (and to prevent the bulb from self-destructing, which is what would happen in an energy efficient fluorescent light without a ballast). Ballasts tended to be very bulky in early CFLs, which made them too big to fit in some fixtures, or caused light-weight tabletop lamps to fall over. This problem has largely been solved, and CFLs today are no larger and not much heavier than their incandescent equivalents (but many people still resist using CFLs because of their early experiences with old, bulky CFLs).

For more details on this topic, see my page How do fluorescent lights work.

Is the mercury in fluorescent lights dangerous?

Mercury is a toxic substance. The amount of mercury used in energy efficient fluorescent bulbs is very small – about 5 milligrams in a typical CFL bulb, ten times that much in a long-tube fluorescent. As long as the bulb remains intact, this mercury is perfectly safe inside the bulb.

When you throw out a fluorescent bulb, be sure to dispose of it safely so that the mercury can be reclaimed and recycled – see Recycling fluorescent light bulbs for more information.

If you break a fluorescent bulb indoors, there is a risk you or someone in your house will be exposed to mercury. The amount of mercury is small – a typical mercury thermometer contains a hundred times more mercury than a CFL – but it is still wise to dispose of the mercury carefully. It is not necessary to seal off the room where the break occurs, but follow these steps to minimize the health risks of any mercury exposure:

  1. Open a window to allow mercury vapors to escape.
  2. Leave the room and close the door. Keep people out for at least 15 minutes.
  3. Clean up without using a vacuum cleaner, which will pull mercury into the vacuum and then shoot it back out through the exhaust vent. Instead follow this process:
    1. Wearing disposable rubber gloves, or plastic bags over your hands, and using stiff paper or cardboard, scoop the pieces onto one piece of the paper or cardboard using the other piece.
    2. Use duct tape or other broad, sticky tape to pick up glass fragments and residue from carpeted areas.
    3. Use a disposable wipe or damp paper towel to wipe up small glass fragments and residue from hard floor areas.
  4. Place all materials, including the broken glass, powder, other parts of the bulb, paper or cardboard, duct tape, wipe or towel, and finally, the disposable gloves, into a plastic bag. Seal the bag closed.
  5. Place the first plastic bag in a second plastic bag and seal that.
  6. Only once you have picked up as much as possible of the fragments and powder as described above, should you vacuum any carpeted areas affected by the breakage. After vacuuming, remove the vacuum bag from the vacuum cleaner, and double bag it. This can safely be disposed of in your outdoor trash but do not leave it in the vacuum or in an indoor trash can.
  7. Throw out any bedding or clothing that has come into direct contact with the broken bulb. Wash any other exposed bedding or clothes in the room where the breakage occurred.
  8. Dispose of the broken bulb as described in the section below.

There is no need to contact an environmental waste disposal company in the case of a single-bulb breakage, contrary to some sensational news reports. Of course, if a large number of bulbs are broken – as I once saw a neighbor do on purpose, smashing a dozen 40-watt 4-foot tube bulbs in his outdoor trash can – you may be at risk for dangerous levels of mercury exposure. Exercise judgment!

How do I dispose of a fluorescent light?

See my page on Recycling fluorescent light bulbs for information on the safe disposal of fluorescent light bulbs. Remember that most fluorescent light bulbs contain trace amounts of mercury, a toxic substance that should be safely recycled. Do not throw your energy efficient fluorescent bulbs in the trash!

Are fluorescent lights more energy efficient than LED lights or halogen lights?

LED house lights are the most energy efficient lights available for home use. Incandescent lights (and halogen lights, which are a particular form of incandescent light), are the least efficient. Fluorescent lights are substantially more efficient than incandescent lights but not as efficient as LEDs.

However, if you have a limited budget for upgrading incandescent or halogen lights, CFLs or other energy efficient fluorescent lights are your best investment, at least for now. Compact fluorescent lights are as much as 40 times cheaper than LED house lights that replace incandescent bulbs, so you can install many CFLs for the price of one LED, and save far more money on electricity.

I don’t like the color that fluorescent lights emit, what options do I have?

Energy efficient fluorescent lights can be purchased in a range of color temperatures, and many are now sold with the same color temperatures as incandescent lights. Color temperature is measured on light bulbs by the Color Rendering Index, or CRI. Look for energy efficient fluorescent lights with a CRI of 70 or higher, or with a color tone advertised as “Soft white” or “Warm white”.

Still, I have to admit I find this objection to energy efficient fluorescent lights a bit surprising. People didn’t keep using kerosene lanterns when the incandescent bulb came around just because they didn’t like the shade of the incandescent. They switched, because they recognized the benefits of not filling their homes with kerosene smoke, and the benefits of reduced fire risk, as well as the cost savings. We live in an era when climate change threatens to cause serious disruptions to our food supply and to the ecosystems that support us, and when smog from coal-fired plants spreads around the globe. A slightly less perfect hue of white (or rather, one we’re not used to, since we didn’t grow up with it) should be an acceptable compromise between our desire for pleasant lighting and our desire for a livable planet.

Can I just replace existing incandescent light bulbs with CFLs?

Generally speaking, you can replace incandescent bulbs with CFLs. However:

  • If the incandescent lights are on a dimmer switch, you must either replace the dimmer switch with a fluorescent-compatible dimmer switch, or replace the incandescent bulbs with CFLs that are designed to work with an incandescent dimmer switch
  • If the incandescent lights are in an enclosed indoor fixture (e.g. a sealed ceiling fixture), the fixture will hold in the heat from the CFLs, which will shorten their lives considerably – potentially making the CFLs as short-lived as the incandescent bulbs they replace.
  • If the incandescent lights are in a ceiling fan fixture, the vibrations from the operation of the ceiling fan may shorten the life of replacement CFLs.
  • If the incandescent lights are placed horizontally, such as in a ceiling light fixture, the replacement CFLs may not last as long, as CFLs are designed to be positioned vertically.

Should I replace all my incandescent light bulbs with CFLs?

I really don’t recommend replacing all your incandescent light bulbs. There are always a few rooms in a house where the lights are used so infrequently, that installing a CFL will never pay for itself in terms of energy savings, such as the light in a furnace room I mention earlier in this article, which might be on only 15 minutes a year.

You should compare the energy savings of replacing an incandescent with a CFL to the energy savings you could obtain some other way with the same money.

If you are trying to save energy to save your own money, spending more on insulation and weatherproofing, or on upgrading heating and cooling equipment or your hot water heater, is a far better investment than putting a CFL in a fixture that is rarely used.

If you are trying to save energy because you’re concerned about climate change, or other forms of pollution created by excessive electricity use, you’ll have more of an impact if you buy CFLs to give to people who don’t have the means to buy their own.

Can I use fluorescent lights on an automatic timer?

You can use energy efficient fluorescent lights on automatic analog timers, as these timers switch the downstream current on or off at the times you choose.

Some electronic timers, on the other hand, send a small amount of downstream current continuously, even in their off setting, and may cause the fluorescent light to try to start itself with this small amount of current. This can damage or shorten the light of the energy efficient fluorescent light. Check your electronic timer for compatibility with a fluorescent light before using it. If you own a Kill A Watt meter or similar home electricity monitoring device, or can borrow one from your local library, you can measure the current coming out of the timer to determine if it does send current downstream when switched off.

Is it better to turn fluorescent lights off and back on, or to leave them on?

You should always turn any light off when you leave a room. Many people are under the mistaken impression that the surge of power when a light is turned on consumes as much energy as leaving the light on for five or even fifteen minutes. This just isn’t true, whether for energy efficient fluorescent lights or any other kind of light. See my separate article Turn off lights for a full explanation.

How reliable are fluorescent lights?

A typical energy efficient fluorescent light lasts 8-10 times longer than an incandescent light, so most of these lights are very reliable. High temperatures shorten fluorescent light bulb life, so enclosing a n energy efficient fluorescent light in a very small space such as an enclosed indoor fixture is not advised.

Most CFLs need to be positioned vertically to last their advertised lifetime; positioning them horizontally, for example in a ceiling light fixture, will shorten their useful life.

Remember that the advertised lifetime of an energy efficient fluorescent or any type of bulb is an average or median lifetime – some bulbs will last far longer, others will not last as long. Lifetimes are expressed in terms of hours of operation. A light that is on for two hours a day and is advertised to last 8,000 hours should last you 11 years.

I have found that some of the more recent brands coming on the market do not last nearly as long as advertised. In some cases I may have used the bulb in an enclosed or horizontal fixture, but in others the bulb just didn’t come close to matching its advertised life. For this reason I recommend sticking with brands that stand behind their product. For example I once bought a GE circular fluorescent tube that burned out after only six months. I phoned GE and complained, and they mailed me a replacement bulb within days, which worked perfectly for years afterwards. By buying only major, reputable brands, you can ensure that you at least have a responsive company to turn to when the product stops working.

How much will I save by installing fluorescent lights?

The savings you will realize depend to a great extent on the price you pay for the energy efficient fluorescent lights, your electricity cost, and how much you use the lights each day. To help you figure out your savings I have created a CFL savings calculator. Here are two example results from the calculator:

  • If you replace a 100 watt incandescent bulb with a 23 watt CFL, based on a replacement cost of $0.49 for an incandescent bulb and $3.00 for the compact fluorescent, assuming $0.10 per kilowatt hour in electricity costs, and two hours of use per day, you should save about $5.70 per year by installing the CFL, and it will pay for itself in 0.43 years (about five months).
  • If you replace the 50 watt incandescent bulbs in a four-bulb fixture with 13 watt CFLs, assuming $0.49 for an incandescent bulb and $2.49 for the CFLs, $0.12/kwh and three hours of use a day, you should save $5.05 per year and the payback period is 0.39 years.

The number of hours used per day is a major factor in how much you’ll save and how soon the light will pay for itself. But don’t forget that if you can switch from incandescent lights to CFLs in a fixture and also reduce the number of hours a day you use the fixture, you will realize even greater savings.

Can fluorescent lights be dimmed?

You cannot dim most energy efficient fluorescent lights with a standard dimmer. You can either purchase a dimmer designed specifically for use with fluorescent lights, or purchase dimmable fluorescent light bulbs, which can be dimmed on a non-electronic incandescent dimmer such as a circular dimmer switch or an analog slider switch.

Dimmable compact fluorescent lights include those listed below. The compact fluorescent lamp manufacturer is followed by the bulb brand name, if applicable.:

  • GE Longlife Plus Soft White Energy Saving Bulb
  • Litetronics Micro Brite dimmable CFLs (5 watts and up)
  • TCP Dimmable Compact Fluorescent (9 watts and up)
  • Neptun dimmable compact fluorescent (14 watts and up). These lights are said to be among the best dimmable CFLs.
  • Global Consumer Products dimmable CFLs (warm white, 15 watt and up

Can fluorescent lights be used outdoors?

Fluorescent lights operate best at typical indoor temperatures. In winter weather, fluorescent lights can take longer to start providing light, and especially if the temperature is below freezing they may not reach maximum brightness. You can enclose outdoor fluorescent lights in a sealed or restricted airflow fixture to improve their light level. For my front porch light, I installed an enclosed fixture and put a CFL in that, and the CFL provides full brightness within a few seconds of being turned on, even on very cold Toronto evenings.

Remember that enclosing a CFL inside a sealed or restricted airflow fixture in warmer weather will shorten the life of the CFL.

Why are some fluorescent lights noisy?

Older fluorescent lights, and early versions of compact fluorescent lights, often made a buzzing sound even when brand new. As fluorescent lights age this buzzing sound may get worse, or may start in lights that previously were silent. This buzzing is caused by the ballast. The ballasts on older fluorescent tube light fixtures, and on older CFLs, were electromagnetic, using a wire coiled many times around an iron core, and using the principal of induction, to limit current flow to the fluorescent tube. Because the alternating current coming from your wall socket switches direction 50 or 60 times a second (50 or 60 Hertz, depending on what country you live in), under certain conditions this very rapid switching of current can cause the core itself to change shape slightly, resulting in the vibration you hear. If the ballast contains plastic filler material to hold the components in place, over time the repeated vibrations may cause the filler to crack and start rattling as well. Over time, the vibrations may also cause other parts of the fixture to loosen, just as bolts on any motorized device may tend to loosen over time with the vibrations of the motor.

Most recent CFLs and other fluorescent fixtures use an electronic ballast, which is both more energy efficient and should not develop a buzzing noise. If a fluorescent light does become noticeably loud over time, you should replace the light (in the case of a CFL) or the ballast (in the case of a fluorescent fixture with ballast).

Another cause of buzzing with compact fluorescent lights is use of the wrong type of dimmer switch. If you have put compact fluorescent lights on an incandescent light dimmer, the lights may buzz and they will last far less time than their rated life. Solve this by replacing the incandescent dimmer with one compatible with compact fluorescents, or by replacing the bulbs with CFLs that are designed to work with incandescent dimmers.

2 replies
  1. Roger Dietz
    Roger Dietz says:

    We recently re-lamped our building with energy efficient florescent lamps. We now have some staff that are getting headaches. Could it be since we replaced the magnetic ballasts with electronic ballests the refresh rate is higher, it could be causing the headaches?

    Thanks for your assistance with this,
    Roger Dietz
    Plant Manager

    • Robin
      Robin says:

      There are a number of factors that may contribute to people reporting increased headaches with a switch of fluorescent lighting.
      One source of headaches with fluorescent lights is the old magnetic ballasts which can cause radio-frequency radiation that is known to cause fatigue, eyestrain, migraines and other symptoms. However you say you switched from magnetic to electronic ballasts, so this should have made the problem better, not worse.
      Another issue is the color temperature of the lights. If you replaced the bulbs at the same time as the lights, you may have also moved from a warmer (lower, more yellow-red) color temperature to a higher (cooler, more blue) color temperature. Higher color temperatures can increase the incidence of migraines in certain people who are light sensitive.
      I am not sure if the higher refresh rate would be a cause of headaches but it is possible.
      Finally, you may have increased lighting levels when you changed the ballasts, to the point where your building is overlit. Excessive lighting can cause headaches in some people.

      If it is possible to restore one section of the building’s lighting to the previous format (or if some of the building is still using the old format) you could test for radio frequency interference (try playing an AM radio close to the lights – radio frequency radiation will cause static on the AM radio), and use a light meter to test the lumens output of the lights, and the color temperature. That might provide some clues.

      But also bear in mind that other changes in the building environment, e.g. air quality, could be behind the increase in reported headaches, and people may just be focusing on the most obvious change they are aware of.


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