CFLs, advanced halogen bulbs, and LEDs can all meet the energy-efficiency requirements of the Energy Independence and Security Act of 2007 as replacements for standard incandescent lamps. As Table 1 shows, CFLs fall between LEDs and advanced halogen lamps in terms of both efficacy—an indicator of the efficiency of the conversion of electricity to light, measured in lumens of light output divided by watts of power input—and longevity.
Table 1: Comparing halogens, CFLs, and LEDs
CFLs are far more efficient than advanced halogen bulbs, but they fall short of LEDs in terms of life and efficacy.
Another alternative is the cold-cathode fluorescent lamp (CCFL). CCFLs 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 lower wattages (from 2 to 18 watts).
CFL shapes and configurations. The most common CFL today is the spiral lamp, but CFLs come in a variety of shapes (Figure 1), each of which provides different light density and distribution and a better fit in certain fixtures. CFL products also come both 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 parabolic aluminized reflector (PAR) lamps. For a guide to which types of lamps work best in different types of applications, visit the Choose a Light Guide created by Energy Star (a voluntary US Environmental Protection Agency program that helps businesses and individuals reduce their use of energy).
Figure 1: CFLs come in many shapes to fit different applications
Although bare spiral lamps are the most common CFL configuration, a wide range of shapes and sizes are available to provide different light densities and distributions and to fit better in certain fixtures. Lamps may also be covered in a variety of ways to mimic different types of incandescent lamps.
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. Today, most CFLs use electronic ballasts, which are lighter, quieter, and more efficient. 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 they’re costly.
Starting method. CFL ballasts 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, such as those that use occupancy sensors, 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.
Figure 2: CFL lamp-and-ballast configurations
CFLs come in three different configurations: self-ballasted, modular, and dedicated. Both modular and dedicated lamps are pin-base configurations.
Pin-base CFLs are designed to be used with a separate ballast—users need to make sure that lamp and ballast are 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 adapter—Edison-style or otherwise—so that 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—two-pin lamps work with magnetic ballasts, and four-pin units work with electronic ballasts. 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-base CFL when it burns out. Because dedicated systems are hardwired and not screwed into a standard screwbase socket, they eliminate the possibility that a user will switch back to an inefficient incandescent bulb when the CFL burns out.
An alternate base for self-ballasted lamps, the GU-24 base—see slide 9 in this Energy Star Electrical Distributors Training presentation (PPT) for an overview of this technology—is designed to replace the Edison socket and base in energy-efficient lighting fixtures while also preventing users from installing incandescent lamps. The GU-24 design gives users more flexibility than a pin-base design (which has a separate ballast that only accepts a bulb with a specific wattage).
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 incandescent bulbs of a certain wattage, but these ratings should be viewed with caution, given that there aren’t any formal standards for 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 of incandescent to CFL wattage yields equivalent light output.