Lighting: Compact Fluorescent Lamps

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 (Table 1). CFL products also come with and without reflectors. Non-reflectorized lamps are usually used in table lamps, floor lamps, and other fixtures designed to put out diffuse light. Reflectorized lamps provide a more directional light. CFLs may also be covered in various ways to mimic standard incandescent lamp shapes, such as A-lamps and PAR 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 (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 sensitive equipment in their operating area. Typical operating frequencies are 20 to 60 kHz. Dimming ballasts are also available, but costs are high.

Starting method. Starting method. CFLs may use one of three different starting methods: preheat, rapid start, and 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 power losses of 3 to 4 watts per lamp. 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). Power losses are lowest 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 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 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 very 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 screw-base socket, dedicated systems eliminate the possibility that a user will switch back to an inefficient incandescent bulb when the CFL burns out.

Wattage. CFLs come in a range of power ratings, from 5 to 28 watts in screw-in versions and up to 55 watts in hardwired models. Manufacturers often claim that the lamps produce light output equal to a certain wattage incandescent; however, these ratings must be viewed with caution, since 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, and low-wattage high-intensity discharge (HID) units. Incandescent lamps may be economical where lights are only occasionally turned on, such as in closets or utility rooms. They also can be the best choice under extremely cold starting conditions and where their specific color characteristics are needed, such as in a retail display.

Halogen units are a type of incandescent lamp that provides a small boost in lamp life and efficacy compared to 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 instead to use one of the new CFL models that are being introduced.

HID lamps have some advantages over CFLs, including better optical control, higher output, and less sensitivity to starting and operating temperatures. However, 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. The newest metal halide lamps being introduced may solve some of these problems.

First, choose a lamp that meets your requirements for shape, light output, and configuration, as discussed above. Then, consider the following:

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. Pin-base CFLs are generally available in four color temperatures: 2,700 kelvin (K), which is similar to the warm tone of standard incandescent lamps; 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. Because CFLs often replace incandescent lamps with color temperatures around 2,700 K, CFL color choice is important when trying to maintain an existing ambience. Most self-ballasted CFLs, which are used as direct replacements for incandescent lamps, are only available at 2,700 K.

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 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.

Pick a lamp suited to the temperature conditions in which it will operate. If you're going to be installing CFLs in a base-down position or 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 provides stable light output over a broad range of temperatures and in various positions.

Make sure that the lamps you chose will not have a negative impact on power quality. Using CFLs in a home will not affect power quality appreciably, but their use in significant quantities 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. CFL manufacturers often state that their product has a high power factor, meaning that its power factor is greater than 0.9, rather than specifying a specific number.

CFL product offerings have expanded a great deal in recent years, with more shapes and larger-wattage products being offered, in increasingly compact sizes. Look for the trend to continue as manufacturers work to decrease lamp size even further while also bringing color quality closer to that of incandescent lamps. Manufacturers are also developing new rapid-start techniques that can extend lamp life while providing a quick start.