Compact fluorescent lamps (CFLs) are a quick, easy replacement for typical screw-base incandescent lamps. CFLs use about one-third as much energy as incandescent bulbs to deliver the same amount of light. They also save on materials and maintenance costs because they last 10 times as long—an average of 10,000 hours compared with fewer than 1,000 hours for an incandescent bulb. CFLs initially cost more—on the order of $2 to $10 (less where utilities provide incentives to buyers or distributors). That’s considerably less than they cost just a few years ago, but it’s still a lot compared with the price of an incandescent lamp (which is typically under $1). Even so, depending on the application, they can pay for themselves pretty quickly. The longer the hours of operation, the shorter the payback period. A CFL operating for typical business hours of 2,500 hours or more per year will pay for itself in less than a year.
Shapes and configurations. CFLs come in a variety of shapes, as shown in Figure 1. The various shapes provide different light densities and distribution and fit better in certain fixtures. CFL products also come with and without reflectors. Nonreflectorized lamps are usually used in table lamps, floor lamps, and other fixtures designed to put out diffuse light. Reflectorized lamps provide more focused light. CFLs may also be covered in various ways to mimic standard incandescent lamp shapes, such as A-lamps and PAR lamps. For a complete guide to which types of lamps work best in different types of applications, visit the Energy Star CFL web page and click on the Choose a Light Guide button.
Ballasts. Ballasts, which control lamp current and provide the required start-up voltage, may be either magnetic or electronic. Most early CFLs used magnetic ballasts, which operate at line frequency—60 hertz (Hz). Electronic units are lighter, quieter, and more efficient. They have replaced magnetic ballasts in virtually all self-ballasted CFLs and in many pin-based CFLs. Electronic ballasts may cause electromagnetic interference with some types of sensitive equipment that may be operating nearby. Typical operating frequencies are 20 to 60 kilohertz. Dimming ballasts are also available, but costly.
Starting method. CFLs may use one of three different starting methods: preheat, rapid start, or instant start. Preheat ballasts heat the lamp electrodes for several seconds before a starter switch allows a voltage of 200 to 300 volts to be applied across the lamp. CFLs with magnetic ballasts may flash on start-up with preheat, but electronic units will not.
Rapid-start units use a low voltage to heat the electrodes quickly and then apply a starting voltage of 200 to 300 volts. The heating voltage is applied even after the lamp starts, leading to small decreases in efficiency. No flashing occurs with rapid-start units. The latest variation is the programmed-start ballast (also called the programmed rapid-start ballast), which more precisely controls the starting process to enable longer lamp life.
Instant-start ballasts allow the CFL to start without delay by supplying a high initial voltage (more than 400 volts). Efficiency is highest with this type of ballast, but lamp life is reduced because the high voltage speeds up the degradation of the emissive coating on the electrodes. In applications with frequent on/off switching, instant-start ballasts will shorten lamp life relative to other ballast types.
Self-ballasted and pin-base configurations. CFLs may be self-ballasted or pin-base, and pin-base units may be either modular or dedicated (Figure 2). Also known as screw-base, screw-in, or integrally ballasted CFLs, self-ballasted CFLs are designed to replace incandescent lamps without requiring any modifications to the existing incandescent lamp fixtures. Self-ballasted CFLs combine a lamp, ballast, and base (the Edison screw base—or, in some countries, another standard base—that fits the incandescent lamp socket) in a single, sealed assembly. Self-ballasted CFLs are most often constructed with T4 (four-eighths inches in diameter) or smaller tubing, but a few designs use T5 tubing. The entire assembly is discarded when the lamp or ballast burns out.
Pin-base CFLs are designed to be used with a separate ballast. As with a linear fluorescent system, the lamp and ballast must be compatible. Pin-base CFLs are available in lower-power versions to replace incandescent lamps and in higher-power versions to replace linear fluorescent lamps or even high-intensity discharge (HID) lamps.
Modular units plug a separate lamp into an Edison or other style of adapter/ballast. With this design, when the lamp burns out, the entire assembly need not be discarded. Instead, a relatively low-cost replacement lamp can be installed in the same ballast base, which typically lasts for 40,000 to 60,000 hours of operation. Lamps for modular units have either two or four pins in their bases. The key disadvantage of modular units is that the pin-base on the lamp and the matching socket on the adapter make modular CFLs larger than self-ballasted CFLs of equivalent light output. The development of low-cost electronic ballasts for self-ballasted CFLs has decreased the cost advantage and popularity of modular systems.
Dedicated systems, also called hardwired systems, feature a ballast and fluorescent lamp socket that are permanently wired into a fixture by the fixture manufacturer or as part of a retrofit kit. As with modular systems, the lamp can be replaced with another compatible pin-based CFL when it burns out. Because they are hardwired and not screwed into a standard screwbase socket, dedicated systems eliminate the possibility that a user will switch back to an inefficient incandescent bulb when the CFL burns out.
A new base for self-ballasted lamps, the GU24, has recently been introduced to make it easier for users to install CFLs of different wattages in an energy-efficient fixture. With the GU24 base, consumers can buy an Energy Star–rated fixture and install a self-ballasted lamp of any wattage that also has a GU24 base.
Wattage. CFLs come in a wide range of power ratings, from 2 to 200 watts for screw-in versions and up to 120 watts for hardwired models. Manufacturers often claim that their lamps produce light output equal to that of incandescents of a certain wattage, but these ratings should be viewed with caution, given that there are no formal standards for making such claims. One manufacturer’s 18-watt product might be labeled as equivalent to a 60-watt incandescent, while a similar product from another vendor might be labeled as a 75-watt equivalent. As a rough guide, a 3:1 ratio, incandescent to CFL wattage, yields equivalent light output.
Other lamp types. For some applications, CFLs compete with incandescent lamps, halogen lamps, low-wattage metal halide lamps, cold cathode fluorescent lamps (CCFLs), and light-emitting diodes (LEDs). Incandescent lamps may be economical where lights are only occasionally turned on, as is often the case in closets or utility rooms. They can also be the best choice where deep dimming is needed, or where their specific color characteristics are important, as for a retail display. However, the Energy Independence and Security Act of 2007 set the efficiency standard for incandescent general-service lamps and is expected to eliminate most of today’s commonly found incandescent general-service lamps. Some advanced incandescent lamps, such as halogen IR lamps, can meet this standard, which will be phased in between 2012 and 2014.
Halogen units are a type of incandescent lamp that provides a small boost in lamp life and efficacy compared with standard incandescent lamps. However, they operate at temperatures high enough to ignite flammable materials and should be used with care. The popular halogen torchieres, for example, have been blamed for a number of fires, and users are encouraged to instead select one of the new CFL models that are available.
Metal halide lamps have some advantages over CFLs, including better optical control, higher output, and less sensitivity to starting and operating temperatures. But they take a long time to warm up and a long time to relight if extinguished, offer fewer color-temperature choices, provide poorer color rendering, and some units flicker at a frequency of 120 Hz. Ceramic metal halide lamps and electronic ballasts have solved some of these problems.
CCFLs are a variation on the CFL that use thicker electrodes and higher voltages than standard CFLs. CCFLs dim much more readily than CFLs and provide longer life (25,000 hours or more). But these lamps cost more than CFLs, are slightly less efficient, and are currently only available in low wattages (from 3 to 8 watts).
LEDs are improving rapidly in performance and decreasing in cost. They can now compete with CFLs in a few applications, notably recessed downlights. However, performance varies widely and LED manufacturers often make exaggerated claims. Energy Star ratings recently became available for some LED applications, which should help users make informed choices.
First, choose a lamp that meets your requirements for shape, light output, and configuration, as discussed above. Then, review the following recommendations.
Choose a CFL that is suitable for the expected conditions. Lamps for use in cold weather should have ballasts rated for cold starting conditions and should work best in sealed fixtures. Exposure to high temperatures, such as those found in reflectorized-can fixtures, can shorten the life of a CFL ballast. Reflector CFLs vetted by the R-CFL Technology Innovation Competition of Pacific Northwest National Laboratory are a good option for recessed cans. These lamps must pass rigorous tests in simulated recessed-can environments. They have demonstrated an average rated life of at least 6,000 hours at elevated temperature and have met minimum specifications for light output, beam angle, and maximum operating temperature. More information on the program and lists of qualified products are available at R-CFL Technology Innovation Competition. If you’re going to be installing CFLs in areas where they will experience temperature extremes (as in poorly vented enclosed fixtures where heat can build up, or in outdoor applications in cold climates), look for products that specifically state that the CFL will provide stable light output over a broad range of temperatures and in various positions. Most CFLs available today, except for circline and high-power twin-tube models, use what is known as amalgam technology, which makes them less sensitive than older models to variations in position and temperature.
Choose a lamp with the appropriate color quality. The correlated color temperature (CCT) of a CFL is a measure of the warmth of its appearance. Lower CCT numbers mean the light will be a warmer white (yellowish), and higher numbers mean it will provide a cooler light (bluish). Most self-ballasted CFLs, which are used as direct replacements for incandescent lamps, are available at 2,700 to 3,000 kelvins (K), which is the temperature of most incandescent lamps they’re designed to replace. This color range works well in most residential settings and enhances warmer colors found in the home. Pin-base CFLs are generally available in four color temperatures: 2,700 K, 3,000 K, 3,500 K, and 4,100 K. Models with color temperatures of 5,000 and 6,500 K are available in certain sizes. Some self-ballasted lamps are available in these higher color temperatures as well. These colors are usually described as “bright white,” “natural,” or “daylight.”
Note that light from products with the same CCT that are made by different manufacturers may look different. Therefore, using lamps from a single manufacturer in a large installation will help to ensure that all of the CFLs will produce the same color effect.
Lighting manufacturers also use another color metric, the color rendering index (CRI), to quantify the color quality of a light source at a given color temperature. The more accurately a source renders a sample of eight standard colors relative to a reference source, the higher the CRI (measured on a scale of 0 to 100). Incandescent bulbs typically boast CRIs close to 100, whereas most CFLs have CRIs ranging from 82 to 85.
Consider power quality. Using CFLs in a home will not affect power quality appreciably, but using significant quantities of them in a large facility can have an impact. In those cases, look for products with low (below 30 percent) total harmonic distortion (THD) and power factors greater than 0.9. High power factors are the norm for pin-based CFLs with electronic ballasts, but it can be harder to find them in self-ballasted CFL products. When CFL manufacturers state that their product has a high power factor, it means that its power factor is greater than 0.9. The power factor of a CFL will not significantly affect its energy-saving benefits for the individual consumer, but the use of CFLs in large numbers—such as in commercial applications or across millions of homes in a distribution system—could require infrastructure upgrades.
Choose dimmable CFLs for dimming circuits. CFLs should not be installed in sockets controlled by incandescent lamp dimmers unless they are specifically labeled as dimmable products. A few dimmable self-ballasted CFLs are available, but they cost two to three times more than nondimmable CFLs and do not generally dim as smoothly or as deeply as incandescent lamps; nor do they shift to a warmer color as they dim—a property that users have come to expect from dimmed incandescent bulbs. Some pin-base CFLs can be dimmed effectively using electronic ballasts similar to those used to dim linear fluorescent lamps, but again, these ballasts are pricey.
Limit the number of CFL types. CFLs are available in a wide variety of sizes and shapes, but in commercial applications it is useful to standardize with just a few types to reduce stocking requirements and confusion at relamping time.
Select a lamp that meets Energy Star requirements. Through the Energy Star program, the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy have developed a set of specifications for cost-effective, energy-efficient CFLs. Manufacturers test their products against these guidelines, and the Energy Star web site spells out the requirements and lists all qualifying products. To find product specifications, lamp options, and more, go to Compact Fluorescent Light Bulbs on the EPA web site.
Use an Energy Star–approved fixture. If you are going to purchase a new fixture, not just a new bulb, choose an Energy Star–approved fixture that does not accept incandescent bulbs but takes only pin-base or GU24-base CFLs. That choice will ensure that the energy savings last and that the light distribution is appropriate for the CFL. See Residential Light Fixtures on the Energy Star web site.
CFL product offerings have expanded a great deal in recent years, with more shapes and higher-wattage products being offered in increasingly compact sizes. Look for this trend to continue as manufacturers continue working to decrease lamp size while bringing color quality closer to that of incandescent lamps.
Manufacturers and others are also taking steps to reduce the impact of the small amounts of mercury used in CFLs. For example, Osram Sylvania offers a CFL recycling service for businesses and consumers. The service provides U.S. Department of Transportation–approved recycling pails and boxes in a variety of sizes. Other manufacturers and retailers are following suit. Manufacturers are also taking steps to reduce the amount of mercury in a CFL. One company, Litetronics, introduced the Neolite line of CFLs, which contain only 1 milligram (mg) of mercury, compared to 4 to 5 mg for the typical CFL. Note that CFLs provide a net reduction in the amount of mercury introduced to the environment because the energy they save compared to incandescent lamps reduces the amount of mercury emitted by the coal-fired power plants that generate about half of the electricity used in the U.S.