Energy efficiency standards that took effect several years ago for fluorescent lighting systems outlawed the manufacture and sale in the U.S. of the most popular (and least efficient) lamps and ballasts used in full-sized fluorescent lighting fixtures. As these low-efficiency components in the existing building stock wear out, and as new systems are installed, U.S. businesses must choose from among a dizzying array of alternatives. Given that roughly 9 out of every 10 U.S. dollars spent over the lifetime of a fluorescent lamp and ballast system goes toward the electric bill, choosing a high-efficiency product that delivers the required lighting performance can reduce lighting bills significantly.

What Are the Options?

Full-size fluorescent lamps differ primarily in their length, diameter, wattage, type of phosphor coating, base/cathode design, and starting method (Figure 1).

Length. For commercial use, 4- and 8-foot lengths are the most common. Four-foot lamps represent about 80 percent of full-size fluorescent lamp sales. Because they are easier to buy, stock, and handle than 8-foot lamps, and because they last longer, they are often tandem-mounted end-to-end in lieu of 8-foot lamps in 8-foot lighting fixtures. About half of the lamps sold for use in 8-foot fixtures are 4-foot lamps.

Diameter. Lamp diameters, in eighths of an inch, are expressed as "T" numbers. T12 lamps (an inch and a half or 12-eights of an inch in diameter) have long dominated fluorescent lamp sales. In recent years, the more efficient T8 lamp has made inroads, but it still accounts for only about 25 percent of lamp sales. T10 and T5 lamps are available but are rarely used in the U.S.

Wattage. Most 4-foot T12 lamps draw 40 watts. So-called "energy-saver" 4-foot T12s typically draw 34 watts, but they also put out less light than their 40-watt counterparts and have a number of limitations. The more efficient 4-foot T8 lamps typically draw 32 watts each and produce nearly as much light as the 40-watt T12s. Among 8-foot lamps, most of the T12 varieties draw from 60 to 75 watts, and most of the 8-foot T8 lamps draw 59 watts.

Phosphor. The most energy efficient coating is "rare-earth" phosphor.

Base. Base designs most commonly used are medium bi-pin and single-pin.

Starting method. There are three basic starting methods for fluorescents: instant start, rapid start, or preheat (Figure 2). Rapid-start lamps are the most commonly used and come in the widest variety of sizes. Note that rapid starting is actually a function of the lamp ballast. Rapid-start lamps are reasonably efficient. Most double-pin T8 rapid-start lamps can also be instant-started, an option that allows flexibility for facilities that want to stock only one lamp but employ both starting types (rapid start for use in shorter duty cycle applications and instant start where the lights will be left on for longer periods). Paired with electronic ballasts, these T8 lamps are the foundation of most energy-efficient fluorescent systems.

A few other categories of lamps are worth noting.

"Energy-saving" lamps. Lamps with this designation use krypton gas in addition to argon gas to suppress both energy consumption and light output. They have several operational limitations: they don't last as long as standard lamps, they're very sensitive to operating current, they can't be deeply dimmed or run on low-ballast-factor ballasts, and they perform poorly in cold temperatures. More important, their use may make it difficult to upgrade to T8s or may convey the impression that they are offering maximum energy savings. When considering energy-saving lamps, compare their rated "mean lumens" with "initial lumens" to assess their long-term performance, and remember that they reduce wattage primarily by reducing light output.

Slimline (instant-start) lamps. Used mostly in 8-foot fixtures by supermarkets, warehouses, and mass-merchandisers, these are instant-start-only, 425-mA, single-pin lamps. Their starting mechanism saves 2 to 3 watts per lamp but is tough on the lamp and reduces its lifetime, which ranges from 7,500 to 15,000 hours—versus 20,000-hour ratings for standard 430-mA rapid-start lamps. These are best used in locations where they remain on for long periods and are not recommended for spaces controlled by occupancy sensors. In many cases, 8-foot or tandem-mounted 4-foot T8 alternatives will give better performance.

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How to Make the Best Choice

Consider the application. How much light is needed for the task? For currently overlit spaces, you can reduce lighting levels by installing lamps with lower lumen output (or fewer lamps); for underlit spaces, install higher-lumen-output lamps. How important is the color quality of the light? The CRI ranges from 52 (for warm white lamps) or 62 (cool white energy-savers) to between the mid-70s and mid-80s for lamps using rare-earth phosphors. The higher a lamp's CRI, the higher its cost.

Consider the whole lighting system. If you are looking for lamps to fit into existing fixtures, you must select lamps that are compatible with the ballasts. T8 lamps cannot be run on ballasts designed for T12 lamps. In many cases, it is cost-effective to replace less efficient magnetic ballasts and T12 lamps in existing fixtures with high-efficiency electronic ballasts and T8 lamps. For new installations, the electronic ballast/T8 lamp combination is also often the most efficient and cost-effective choice.

Consider lifecycle cost. Because energy accounts for nearly 90 percent of the lifecycle cost of owning and operating a fluorescent lighting system, it generally pays to buy the most efficient equipment available that will deliver the amount and quality of light for the task (Figure 3 and Figure 4). Lamp first costs vary up to five-fold but are virtually irrelevant, because they account for only 1 to 2 percent of the lifecycle operating and maintenance expense of the lighting system.

High-performance lighting is a subtle art, and there is no one "right" lighting solution for all situations. In many general lighting applications, the following represent good choices:

• Use T8 lamps with electronic ballasts in most applications.

• Use 4-foot lamps. This is the most common length and is the cheapest and easiest to buy, stock, and handle.

• Use standard-output lamps. High-output (HO) and very-high-output (VHO) lamps make sense in niche applications, but they are more costly and less efficient than standard-output lamps, their light output falls more rapidly over time, and they require heavy, oversized ballasts.

• Select lamps with a color rendering index of 70 to 80. For most purposes this is plenty of color rendering and is far superior to the old "cool-white" halophosphor lamps. Lamps with a CRI above 80 are considerably more expensive and may be worthwhile in retail or other color-sensitive applications.

• Select lamps with a color temperature of 3,500 K. This is a good middle ground that can blend acceptably with warmer incandescents and cooler daylight and HID sources.

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What's on the Horizon?

Fluorescent lamps are a mature technology, but manufacturers continue to make incremental improvements in efficiency and lamp life.

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Who are the Manufacturers?