Compact Fluorescent Light Bulbs

A compact fluorescent lamp (CFL) is a common name given to a whole family of small, single-ended fluorescent light bulbs with folded, bridged, or spiral glass tube designs. CFLs use significantly less energy than a traditional incandescent light bulb while emitting a similar light output.

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CFL Information


CFL stands for compact fluorescent lamp. It is a small fluorescent light bulb that uses about 65% to 75% less energy than a traditional incandescent light bulb and can either be screwed into a regular light bulb socket or plugged into a bayonet-type socket.

Color Temperature

Compact fluorescent lamps labeled “warm white” or “soft white” produce light like typical incandescent light bulbs. CFLs that have a cooler color (similar to bright white incandescent bulbs) are usually labeled “bright white” or “daylight” on the product packaging. (Editorial Advice: The color labeling on ENERGY STAR® qualified CFLs carries a good deal of credibility since color temperature is one of the factors that the ENERGY STAR® program pays close attention to.)


If the light fixture is controlled by a dimmer, use a special compact fluorescent lamp that has been specifically designed to work in these applications. (Editorial Advice: Even when using ENERGY STAR® dimmable CFLs the range of dimmability is often very limited. Furthermore, if a non-dimmable CFL is used in this type of situation, the CFL may overheat and become a fire hazard.)


Burned-out compact fluorescent lamps should not be thrown out with the rest of the trash. Instead, CFLs should be properly disposed of by recycling them.


For recessed downlight fixtures with screw-in sockets, it is probably better to use a self-ballasted reflector CFL than a self-ballasted spiral CFL since the design of the reflector evenly distributes the light down to your task area.

Energy Savings

In general, compact fluorescent lamps use less than 1/3 of the energy required to power a traditional incandescent light bulb to produce the same amount of light. The non-profit organization, Earth Policy Institute (EPI), estimates that the USA could close 80 coal-fired power plants if Americans switched over, ne masse, to compact fluorescent lamps. A global shift, says EPI could close some 270 power plants worldwide. According to the US Environmental Protection Agency (EPA), if every American home replaced just one incandescent light bulb with an ENERGY STAR® qualified CFL, we would save enough energy to light more than 3 million homes for a year, which represents more than $600 million in annual energy costs.


In the United States and Canada, the ENERGY STAR® program labels compact fluorescent lamps that meet a set of standards for starting time, life expectancy, color, and consistency of performance. The intent of the program is to reduce consumer concerns due to variable quality of products. For example, those CFLs with a recent ENERGY STAR® certification start in less than one second and do not flicker.

Greenhouse Gases

According the US Environmental Protection Agency (EPA), if every American home replaced just one incandescent light bulb with an ENERGY STAR® qualified compact fluorescent lamp, we would prevent greenhouse gases equivalent to the emissions of more than 800,000 cars.


Compact fluorescent lamps get warm during operation; so, some CFLs are labeled not to be used in the base-up position, since the heat will shorten the life of the ballast. Because of this, some CFLs are not suitable for use in pendant lamps and especially not suitable for recessed lighting fixtures. However, special CFLs intended for use in such fixtures are available. Current recommendations for fully enclosed, unventilated light fixtures (such as those recessed into insulated ceilings) are either to use special reflector CFLs or to replace the entire recessed fixtures with those designed for CFLs.


You can use compact fluorescent lamps in high humidity areas like bathrooms; however, high humidity can shorten the life of CFLs. To avoid moisture problems generally, control the humidity in your bathroom by running your ventilating fan during and 15 minutes after showers and baths. 

Lumen Depreciation

All fluorescent lamps (including CFLs) get dimmer over their lifetime; thus, a CFL that starts out providing adequate illumination may produce an inadequate amount of light later in its life. This light output depreciation is exponential with the fastest losses taking place soon after the CFL was first used. By the end of their lives, CFLs can be expected to produce 70-80% of their original light output. A 20-30% reduction over many thousands of hours represents a change which is often barely noticeable in everyday life.

Manufacturer Differences

There are large differences among the quality of light, the cost, and the turn-on time among CFLs made by different manufacturers, even for CFLs that appear identical with the same wattage, shape, and color temperature. (Editorial Advice: To minimize any problems encountered with the use of CFLs Pegasus Associates Lighting recommends that you use CFLs that have been certified as ENERGY STAR® compliant.)

Mercury Content in CFLs

Like all fluorescent lamps, each compact fluorescent lamp contains a trace amount of mercury. A CFL usually contains 4-5 milligrams, the amount that would cover the tip of a ballpoint pen. Some manufacturers have reduced the amount of mercury in their CFLs to 1.4-2.5 milligrams per light bulb. By comparison, older mercury thermometers contain about 500 milligrams of mercury – an amount equal to the mercury in 125 standard CFLs. Mercury is an essential part of CFLs; it allows the CFL to be an efficient light source. It is important to note that no mercury is released when the bulbs are intact (not broken) or in use. However, mercury is a toxic heavy metal and exposure to mercury can cause a wide range of health problems, including damage to the central nervous system, kidneys, and liver. (Editorial Advice: To minimize the amount of mercury in a CFL Pegasus Associates Lighting recommends that you select CFLs that have been specifically manufactured with very little mercury content, such as GE ECO CFLs, Osram-Sylvania Ecologic CFLs, Philips Alto CFLs, and others.)

Mercury Emissions from Coal-Fired Electrical Power Plants

The US Environmental Protection Agency estimates that the U.S. is responsible for the release of 104 metric tons of mercury emissions each year. Most of these emissions come from coal-fired electrical power plants. Mercury released into the air is the main way that mercury gets into water and bio-accumulates in fish. (Eating fish contaminated with mercury is the main way for humans to be exposed.) Most mercury vapor inside fluorescent light bulbs becomes bound to the inside of the light bulb as it is used. The EPA estimates that the rest of the mercury within a CFL – about 11 percent – is released into the air or water when it is sent to a landfill, assuming the light bulb is broken. Therefore, if all 290 million CFLs sold in 2007 were sent to a landfill (versus recycled, as a worst case scenario) – they would add about 0.13 metric tons, or 0.1%, to U.S. mercury emissions caused by humans. Electricity use is the main source of mercury emissions in the U.S. CFLs use less electricity than incandescent lights, meaning CFLs reduce the amount of mercury into the environment. A 13-watt, 8,000-rated-hour-life CFL (60-watt equivalent; a common light bulb type) will save 376 kWh over its lifetime, thus avoiding 4.5 mg of mercury being released into the atmosphere. If that CFL goes to a landfill, overall emissions savings would drop a little, to 4.2 mg.

The EPA recommends that CFLs are recycled where possible, to maximize mercury savings. Because CFLs also help to reduce greenhouse gasses, other pollutants associated with electricity production, and landfill waste (because the bulbs last longer), they are clearly the environmental winner when compared to traditional incandescent light bulbs.

Outdoor Use

Compact fluorescent lamps that are not designed for outdoor use may perform poorly in cold weather. The light output of CFLs drops at low temperatures and they sometimes fail to operate at all at very low temperatures. However, special CFLs that are manufactured with cold-weather ballasts may be rated to operate as low as -23°C (-9°F).

Rated Life

The average rated life of a compact fluorescent lamp is between 8 and 15 times that of a comparable incandescent light bulb. CFLs typically have a rated life of between 6,000 and 15,000 hours, whereas incandescent lamps are usually manufactured to have a rated life of 750 hours to 1,000 hours, although some long-life incandescent light bulbs are manufactured to have a rated life of as much as 20,000 hours. The lifetime of any lamp, including CFLS, depends on many factors including operating voltage, manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off, lamp orientation, and ambient operating temperature, among other factors. The life of a CFL is significantly shortened if it is only turned on for a few minutes at a time. In the case of a 5-minute on/off cycle the lifespan of a CFL can be up to 85% shorter, reducing its lifespan to the level of an incandescent lamp. The US ENERGY STAR® program recommends that CFLs be left on at least 15 minutes at a time to mitigate this problem.

Self-Ballasted CFLs

A self-ballasted or integrated compact fluorescent lamp combines an electronic ballast with a glass tube and some type of screw-in or bayonet base into a single CFL unit. These integrated CFLs allow consumers to more easily replace incandescent lamps with CFLs, which generally can work well in standard incandescent light fixtures. This technique lowers the cost of using CFLs since they can reuse the existing incandescent light fixtures, which are usually relatively inexpensive.


CFLs are some times larger than their incandescent equivalents. This means that a CFL might not fit well in existing light fixtures. Thus, before buying a large quantity of CFLs, first test one in several locations.

Starting Time

Incandescent light bulbs provide light almost immediately (approximately 0.1 second) upon the application of voltage. Compact fluorescent lamps, however, may provide as little as 50%-80% of their rated light output (lumen rating) at initial switch on and take a perceptible time (up to 3 minutes) to achieve full brightness. This slow starting time is further exacerbated by very cold temperatures and the aging of the CFL. These data are affected by a multiplicity of factors such as the manufacturer of the CFL, the type of CFL, the wattage of the CFL, and the light fixture in which the CFL is being used.

Timers, Use of

Electronic (but not mechanical) timers can interfere with the electronic ballasts in compact fluorescent lamps and shorten their lifespan.

Wattage Range

The wattage of compact fluorescent lamps can range from 3 watts to 200 watts.

UV Rays

To learn whether UV Rays are a problem in CFLs check out our blog post “CFLs and UV Rays: Is There Really a Problem?”

CFL Base Types

Compact Fluorescent Base Types

Infographic – A Guide to CFL’s

CFL Guide