A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb or an energy saving lightbulb, is a type of fluorescent lamp that screws into a regular light bulb socket or plugs into a small lighting fixture.

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

Market

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 a screw 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.

Comparing CFLs and incandescent bulbs

CFLs are typically guaranteed for 8,000 hours. (Incandescent bulbs typically last 500 to 4000 hours, depending on exposure to voltage spikes.)

CFLs use about four times less electricity. For example, a 15-watt CFL produces the same amount of light as a 60-watt incandescent bulb (approximately 900 lumens). Let us compare the purchase and operating costs of these two light sources.

The kilowatt-hour (kWh) is the unit of energy used to sell electricity in most countries. The cost of electricity in the United States ranges from $0.06 to $0.38 per kWh, with an average cost of $0.09 per kWh. (See Electricity Rates.)

For convenience, a rate of $0.10 per kWh is often used for estimating the running costs of appliances.

Colors

CFLs are produced in varying shades of white:

• "Warm white" (2,700 K) provides a light extremely similar to that of an incandescent bulb, somewhat yellow in appearance;

• "Soft white" (3,500 K) bulbs produce a yellowish-white light;

• "Cool white" (4,100 K) bulbs emit more of a pure white tone; and

• "Daylight" (6,400 K) is slightly bluish-white.

The "K" numbers denote the color temperature in kelvins. Color temperature is a quantitative measure. The higher the number, the "cooler", i.e. bluer, the shade.

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

• Red, green, and pink, primarily for novelty purposes;

• Yellow, for outdoor lighting, does not attract insects; and

• Blacklight, for special effects.

CFLs are an efficient source of "long wave" ultraviolet light, dozens of times more efficient than incandescent "blacklight" bulbs.

Being a gas discharge lamp, a CFL will not generate all frequencies of visible light; the actual color rendering index is a design compromise (see below). With less than perfect color rendering, CFLs can be unsatisfactory for inside lighting, but modern, high quality designs are proving acceptable for home use.

Environmental concerns

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, where the mercury from many bulbs escapes and contributes to air and water pollution.

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 will recycle them correctly; or

• Bring used CFLs to a local recycling facility.

Reflector CFL

The first step of processing involves crushing the bulbs in a machine that uses negative pressure ventilation and a mercury-absorbing filter 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

There are two main parts to a CFL: the gas-filled tube (also called bulb or burner) and the magnetic or electronic ballast. Electrical energy in the form of an electrical current from the ballast flows through the gas, causing it to give off ultraviolet light. The ultraviolet light then excites a white phosphor coating on the inside of the tube. This coating emits visible light. CFLs that flicker when they start have magnetic ballasts; CFLs with electronic ballasts are now much more common. See Fluorescent lamp.

End of life

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 fail due to cracks and imperfect seals and due to electrode decomposition (from vaporization of the metal).

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.

Design compromises and challenges

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.)

• Covered performance: To approximate the look of an incandescent bulb, the CFL burner can be enclosed behind a cosmetic glass cover. However, this causes the temperature of the burner to increase greatly, increasingly the gas pressure inside the burner and decreasing the brightness (and therefore efficiency) of the lamp. These problems have largely been solved using special mercury compounds and other techniques, and now globe and flood versions are widely available (at hardware stores and elsewhere).

• 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 electronics with low levels of electronic distortion to avoid disturbing the electricity supply, usually not a problem with home use.

• 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.

   

Other CFL technologies

Another type of CFL is the radiofluorescent lamp (RFL), which uses radio waves instead of an electric current to ionize the mercury to produce the ultraviolet light used to excite the phosphors. Another variant is coated (inside the bulb) with titanium dioxide, which the manufacturer claims reduces odors by ionization and oxidation.

The Cold Cathode Fluorescent Light (CCFL) is one of the newest forms of CFL. CCFLs produce less heat, are more energy efficient, are more compact, and last longer than conventional CFLs.

Cite: Wikipedia