A spiral type of compact fluorescent light bulb

Despite the slightly reduced efficiency of this style CF bulb due to the inherent excessively thick layer of phosphor on the lower side of the twist, it has remained one of the most popular among North American consumers since its introduction in the mid 1990s.

A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb or an energy saving light bulb, is a type of fluorescent lamp that fits into a standard light bulb socket.

In comparison to incandescent light bulbs, CFL light bulbs have a longer-rated life and use less electricity.  In fact, CFLs save enough money in electricity costs to make up for their higher initial price within about 500 hours of use. 

Globally introduced in the early 1980s, CFLs have steadily increased in sales volume, largely due to improvements in product performance and reduction in unit prices.  The most important advance in fluorescent lamp technology (including in CFLs) has been the gradual replacement of magnetic ballasts with electronic ballasts:  This has removed most of the flickering and slow starting traditionally associated with fluorescent lighting.

The market for CFLs has been aided by the production of both integrated and non-integrated lamps.  Integrated lamps combine a bulb, an electronic ballast and either a screw or bayonet fitting; these lamps allow consumers to easily replace incandescent bulbs with CFLs.  Non-integrated lamps allow for the replacement of consumable bulbs and the extended use of ballasts; since the ballasts last longer, they can be more expensive and sophisticated, providing options such as dimming.  (Non-integrated CFLs are more popular for professional users, such as hotels.)

CFLs are produced for both AC input and DC input.  DC CFLs are popular for use in recreational vehicles and off-the-grid housing.  Poor families in developing countries are using DC CFLs (with car batteries and small solar panels) to replace kerosene lanterns.

The kilowatt-hour (kWh) is the unit used to sell electrical energy in most countries.  The cost of electricity in the United States ranges from $0.06 to $0.38 per kWh, with an average cost in May 2006 of $0.106 per kWh.  For convenience, a rate of $0.08 per kWh is often used for estimating the running costs of appliances.

The CFL, therefore, will save $36.00 in electricity (compared to the incandescent bulb) during its rated life.  Some American discount stores sell packages of CFLs for about $2.75 per CFL and incandescent bulbs for about $0.50 each, a $2.25 difference.  The estimated payback period for buying the CFL instead of the incandescent bulb is, therefore, 500 hours, which is 100 days at 5 hours per evening.  Two additional advantages of the CFL are that the majority of these bulbs never get beyond touch-warm, making them significantly safer for children and the elderly, and providing a reduced risk of fire in homes and offices.

• As of early 2007, blister packs of CFLs in U.S. discount stores made pricing per bulb rapidly approach $1, partly influenced by a push by retailer Wal-Mart to give CFLs more in-store prominence, and expanding the range of available wattages down to 5 watts (25 watts tungsten equivalent), agreed to with some reluctance by manufacturers of both tungsten and CFL bulbs, who enjoy a significantly larger margin in the tungsten product.  A California initiative even seeks to ban the sale of tungsten bulbs altogether.

The above calculations do not account for the ancillary effect of (light bulb) heat on energy costs.  The energy that is not used to create light is instead converted into heat energy.  Incandescent bulbs therefore produce substantially more heat than CFLs for a given light output.  During cold months, incandescent bulbs can help to heat buildings; but during hot months, incandescent bulbs place additional strain on air conditioning systems.

A photograph of various light bulbs illustrates the effect of color temperature differences (left to right):  1. Compact Fluorescent:  General Electric®, 13 watt, 6500 K; 2. Incandescent:  Sylvania® 60-Watt Extra Soft White; 3. Compact Fluorescent:  Bright Effects, 15 watts, 2644 K; 4. Compact Fluorescent:  Sylvania®, 14 watts, 3000 K.

CFLs are produced in varying shades of white: 

• “Warm white” or “Soft white” (2700 K-3000 K) provides a light very similar to that of an incandescent bulb, somewhat yellow in appearance;
• “White”, “Bright White”, or “Medium White” (3500 K) bulbs produce a yellowish-white light, whiter than an incandescent bulb but still on the warm side;
• “Cool white” (4100 K) bulbs emit more of a pure white tone; and
• “Daylight” (5000 K-6500 K) is slightly bluish-white

The “K” denotes the correlated color temperature in Kelvins.  Color temperature is a quantitative measure.  The higher the number, the “cooler”, i.e., bluer, the shade.  Color names associated with a particular color temperature are not standardized for modern CFLs and other triphosphor lamps like they were for the older style halophosphate fluorescent lamps.  Variations and inconsistencies exist among manufacturers.  For example, Sylvania’s® Daylight CFLs have a color temperature of 3500 K, while most other bulbs with a “daylight” label have color temperatures of at least 5000 K.  Some vendors do not include the Kelvin value on the package, but this is beginning to change now that the Energy Star Criteria for CFLs is expected to require such labeling in its 4.0 revision.

CFLs are also produced, less commonly, in other colors: 

• Red, green, orange, blue, and pink, primarily for novelty purposes
• Yellow, for outdoor lighting, because it does not attract insects
• Blacklight, for special effects

CFLs with UVA generating phosphor are an efficient source of long wave ultraviolet “blacklight”, much more efficient than incandescent “blacklight” bulbs, since the amount of UV light that the filament of the incandescent lamp produces is according to blackbody radiation, and the UV radiation is only a fraction of the generated spectrum.

• Full Spectrum
• High Definition

Since CFLs use about 1/4 of the energy of incandescent bulbs they are a key part of efforts to fight pollution.

Mercury use of compact fluorescent bulb vs. incandescent bulb
when powered by electricity generated from coal.

However, CFLs contain trace amounts of mercury.  The amount is not large enough to pose a hazard to users, but it does become a concern at landfills and trash incinerators where the mercury from many bulbs can escape and contribute to air and water pollution.

Some manufacturers such as Philips® and GE® make very low mercury content CFLs.  Safe disposal requires storing the bulbs unbroken until they can be processed.  Consumers should seek advice from local authorities.  Usually, one can either: 

• Bring back used CFLs to where they were purchased, so the store can recycle them correctly; or
• Bring used CFLs to a local recycling facility.

The first step of processing involves crushing the bulbs in a machine that uses negative pressure ventilation and a mercury-absorbing filter or cold trap to contain and treat the contaminated gases.  Many municipalities are purchasing such machines.  The crushed glass and metal is stored in drums, ready for shipping to recycling factories.

Note that coal power plants are the single largest source of mercury emissions into the environment.  According to the Environmental Protection Agency (EPA), (when coal power is used) the mercury released from powering an incandescent bulb for five years exceeds the sum of the mercury released by powering a comparably luminous CFL for the same period and the mercury contained in the lamp.

How they work

Both the ballast and the burner are subject to failure from normal use.  In low-quality CFLs, high temperatures often cause the ballast electronics to fail before the burners.  In high-quality CFLs, the burners almost always fail first.  The burners occasionally fail due to cracks and imperfect seals but much more typically due to an increased work function at the electrodes caused by vaporization and sputtering-off of the cathode material.  It is also this material that then deposits onto the burner’s glass tubing, causing blackening of the tubing.

High-quality driver electronics can prolong the life of the burners by preheating the electrodes to prevent damage from rapid expansion.  High-quality drivers require high-quality components.  The best CFL manufacturers (including Osram®, Philips®, General Electric® and Luxlite®) produce CFLs that can last 15,000 hours.  Such lifetimes require highly automated and controlled manufacturing.

At end of life, CFLs should be recycled by specialist firms.  In the European Union, CFL lamps are one of many products subject to the WEEE recycling scheme.  The retail price includes an amount to pay for recycling, and manufacturers and importers have an obligation to collect and recycle CFL lamps.

Apart from durability, the primary purpose of good CFL design is high electrical efficiency.

These are some other areas of interest: 

• Quality of light:  A phosphor emits light in a narrow frequency range, unlike an incandescent filament, which emits the full spectrum, though not all colors equally, of visible light.  Mono-phosphor lamps emit poor quality light; colors look bad and inaccurate.  The solution is to mix different phosphors, each emitting a different range of light.  Properly mixed, a good approximation of daylight or incandescent light can be reached.  However, every extra phosphor added to the coating mix causes a loss of efficiency and increased cost.  Good-quality consumer CFLs use three or four phosphors — typically emitting light in the red, green and blue spectra — to achieve a “white" light with color rendering indexes (CRI) of around 80.  ,A CRI of 100 represents the most accurate reproduction of all colors; reference sources having a CRI of 100, such as the sun and tungsten bulbs, emit black body radiation.)
• Size:  CFL light output is roughly proportional to phosphor surface area and high output CFL bulbs are often larger than their incandescent equivalents.  This means that the CFL might work fine in the socket, but that the light cover might not fit over it or that the user might not have the room to squeeze the CFL in place.
• Electronics:  Dimming control can be added to the lamp with support from the driver electronics.  Also, large deployments of CFLs (in a hotel lobby, for example) require specialized electronics with low levels of electronic distortion to avoid disturbing the electricity supply.  This is usually not a problem with home use because of the few lamps deployed.  One problem with dimmable compact fluorescents is that when they dim the color temperature stays the same.  This means that a dimmed light appears grey instead of warm orange like a incandescent light when dimmed Time to achieve full brightness:  Compact fluorescent bulbs can take 30 seconds or more to reach full brightness.  This compares to 0.1 seconds for incandescent bulbs and 0.01 seconds for LED lamps.
• CFLs often do not fail suddenly like incandescent light bulbs do.  Symptoms of impending CFL failure may come months ahead, with more and more prolonged turn-on times until full luminosity is reached, buzzing of the ballast, random periods of reduced brightness and the appearance of growing black spots on the glass tubing’s inside.
• In places infested with insects or in an outdoor environment bugs have a habit of climbing into the “cage” formed by the CFL tubing and perishing inside.  Some CFLs have an extra oval shell hiding the tube works to prevent this.
• Buzz:  The newer spiral lights have very low hum or buzz, but in a very quiet room can still be heard.  This can be annoying to some people.
• Outdoor Use:  In very cold weather the time to full brightness can be extended to several minutes or not turn on at all.
• Differences between manufacturers:  There are large differences between quality of light, cost, and turn-on time between different manufacturers, even for bulbs that appear identical and have the same color temperature.

All LIFE GUARDIAN™ smoke/CO detectors utilize CFL bulbs in order to give you the equivalence of a conventional 75-100 watt tungsten bulb while reducing the amount of ambient heat reaching the photoelectric chamber in our detectors.

Another type of fluorescent lamp is the electrode-less fluorescent, known as a radio fluorescent lamp or fluorescent induction lamp.  Unlike virtually all other conventional lamps that have hardwired electrical connections to transfer energy to the lamp core, the electrode-less fluorescent accomplishes this solely by electromagnetic induction.  The induction is effected by means of a wire-wound ferrite core that projects upward into the bulb encased in an inverted U-shaped glass cover.  The wire is energized with high frequency electricity often 2.65 or 13.6 MHz; this ionizes the mercury vapor, exciting the phosphor & producing light.

Another variation on existing CFL technologies are bulbs with an external nano-particle coating of titanium dioxide.  Titanium dioxide is a photo catalyst becoming ionized when exposed to UV light produced by the CFL, thereby capable of converting oxygen to ozone, water to hydroxyl radicals, which neutralizes odors and kills bacteria, viruses, and mold spores.

The Cold Cathode Fluorescent Light (CCFL) is one of the newest forms of CFL.  CCFLs use electrodes without a filament.  The voltage of CCFL lamps is about 5 times higher than CFL lamps and the current is about 10 times lower.  CCFL lamps have a diameter of about 3 millimeters.  The lifetime of CCFL lamps is about 50,000 hours.  The lumens per watt is about half of CFL lamps.

Initially CCFL was used for thin monitors and backlighting, but now it is also manufactured for use as a light bulb.  Since the efficacy (watt/lumen) is actually lower than a compact fluorescent light, it is actually not as efficient as a CFL.  Its advantages are that it is (1) instant-on, like an incandescent, (2) compatible with timers, photocells, and dimmers, and (3) has an amazingly long life of approximately 50,000 hours.  CCFL are a convenient transition-technology for those who are not comfortable with the short lag-time associated with the initial lighting of Compact Fluorescents.  They are also an effective and efficient replacement for lighting that is turned on and off frequently with little extended use ,e.g.: a half-bath or closet).

Efforts to encourage adoption

Improving the efficiency of household lighting is part of the effort to increase energy efficacy.  However, people have been hesitant to transition from incandescent bulbs to CFLs, despite their three- to twelve-month payback period.  The initial capital investment is higher, which may deter some people.  The warm-up period associated with CFLs discourages others (although the new CCFL mitigate that objection).  Professionals who install lighting fixtures sometimes do not consider installing CFLs, because the electrical bill is not their concern, and the CFLs have a higher cost.

Some governments have attempted to encourage CFL usage by distributing them for free and by appealing to people’s moral beliefs.  Some activists in Britain have lobbied Parliament to tax or ban incandescent bulbs, a measure that has generated controversy, and websites like Banthebulb.org have been created in support of the ban.

In June 2006, the U.S. Environmental Defense initiated a campaign called “Make the Switch” to encourage the public to switch from incandescent bulbs to compact fluorescent bulbs.  It asked every household in the U.S. to replace three 60-watt incandescent bulbs with CFLs.  Environmental Defense claims that if every household was to do this, the change could reduce pollution as much as taking 3.5 million cars off the road would.

In addition, Wal-Mart® announced in September 2006 that it was starting a campaign to endorse CFLs.  The store aims to sell one CFL to every one of their 100 million customers within the next year, thus changing the energy consumption of the United States and improving Wal-Mart’s reputation.  In Ottawa, Canada, there is an effort to get every household to change at least one light bulb.  Project Porchlight has volunteers going door-to-door providing one CF bulb to every household for free.

Another website, Onebillionbulbs.com, is behind a campaign to replace one billion incandescent bulbs with CFLs across the U.S.  The site has a fifty-state map; each state is a certain color from white to green.  The closer to green in color, the closer to the state’s goal.

A California Assemblyman (representing the 40th Assembly District), Lloyd Levine, introduced a bill (“How Many Legislators Does it Take to Change a Light Bulb?”) to ban the sale of incadescent light bulbs in the State of California by the year 2012.

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