Full-size fluorescent systems are an efficient source of lighting for general lighting applications in commercial, institutional, and industrial spaces with low to medium ceiling height. LED lighting is quickly replacing fluorescent lamps since it’s more effective, has comparable costs, and works well with controls. However, fluorescent lighting can serve as an alternative if cost is an issue, and you aren’t adding controls.
How much energy a fluorescent lighting system uses depends on the efficiency of the lamps, ballasts, fixtures, and controls. To implement fluorescent lamps successfully, consider lamp options—diameter, length, and phosphor blend—as well as the options for ballasts and fixtures.
What are the options?
General lamp characteristics
All full-size fluorescent lamps differ in several ways, including lamp size, phosphors used, and starting method.
Lamp sizeFluorescent lamps range from 0.250 to 2.125 inches in diameter (figure 1) and from 6 to 96 inches in length. Diameter is specified by “T” and the size in eighths of an inch; for example, a T12 lamp is 12/8 inch (1.5 inches) in diameter. Four-foot lamps are the most common length and the cheapest and easiest to buy and stock. Eight-foot lamps are slightly more efficient, but they can break more easily and be difficult to transport.
Phosphors are the substances that coat the inside of fluorescent tubes and transform the ultraviolet light that’s generated by an electric arc into visible light. The phosphor blend determines the color temperature and color rendering of the light emitted by the lamp. Halophosphors are the least expensive and lowest-quality phosphors. Commodity-grade T12 lamps use halophosphores to produce cool white and warm white colors. Rare-earth phosphors are more expensive but produce a higher-quality light and enable fluorescent lamps to maintain their light output over a longer time. Standard T8s use a blend of these two types, while high-performance T8s primarily or exclusively use rare-earth phosphors.
Linear fluorescent lamps fall into three families based on how they start: preheat start, instant start, and rapid start (figure 2).
Preheat start is also known as “switch start.” There are also several variations on rapid-start technology. The ballast’s design determines what type of starting method the fluorescent lamp can use; the lamp must be compatible with the ballast’s starting mode to ensure proper operation.
- Preheat-start lamps. Preheat-start lamps are, in general, short (6 to 36 inches) and use low-cost, low-performance phosphors. However, new versions with good color rendering are available. Preheat-starting lamps typically use magnetic or resistive ballasts. Preheat-starting degrades the lamp’s electrodes more rapidly than other starting methods, so preheat-start lamps have short lifetimes. Users seeking to maximize energy efficiency should avoid preheat-start lamps when possible.
- Instant-start lamps. Instant-start lamps generally operate with the most efficient type of ballast, but this type of ballast yields the shortest lamp life because of the frequent switching on and off. If you’re going to use instant-start lamps, a good rule of thumb is to ensure that averaging operating time per start of the lamps is more than three hours. Instant-start lamps aren’t a good fit for spaces using occupancy sensors to control lighting because occupants may trigger frequent on/off switching, which shortens their lamp life. If the average operating time per start will be significantly less than three hours, then rapid-start lamps would be a better choice. Supermarkets and mass merchandisers mainly use 8-foot instant-start lamps.
- Rapid-start lamps. The newest version of a rapid-start ballast is the programmed-start ballast, also known as programmed rapid-start ballast. In almost all cases, these ballasts maximize lamp life but are slightly less efficient. They’re the best choice in applications where lights will frequently turn on and off and are a good choice to pair with occupancy sensors.
Types of fluorescent lamps
Standard T8 fluorescent lamps offer better efficiency, lumen maintenance, color quality, fixture optics, and life-cycle costs than antiquated T12 systems. However, several other options now offer even better performance for most applications.
Premium fluorescent lighting technology has achieved higher levels of efficiency, color quality, and longevity in a class of products called high-performance T8s (sometimes called super T8s). Most of these products have a higher price tag but are more-cost-effective replacements for T12s than standard T8s (figure 3). In many cases, high-performance T8s can also cost-effectively replace standard T8s. Since many buildings use standard T8s that they installed during previous efficiency upgrades, high-performance T8s can provide another round of cost and energy savings as the next step in retrofitting. Today’s high-performance T8 lamp-and-ballast combinations can improve system performance by 70% to 81% over a T12 “energy-saver” lamp and magnetic ballast combination, and by 23% to 31% over their most common modern predecessor—the standard 700-series, rare-earth-phosphor T8 lamp and standard instant-start electronic ballast combination.
The Consortium for Energy Efficiency (CEE) set specifications for high-performance T8 lamps to provide a voluntary national standard for lamp-and-ballast systems that energy service providers can use in their programs. The CEE specifications for a 4-foot, high-performance T8 lamp with a nominal wattage of 32 watts or less include the following key criteria:
- Produces 3,100 or more initial lumens and maintains at least 2,900 mean lumens
- Achieves 94% lumen maintenance
- Provides a color rendering index (CRI, or how well a light source renders colors) of 81 or higher
- Achieves a rated life of 24,000 hours or more at three hours per start on a rapid-start or programmed rapid-start ballast
Reduced-wattage and other T8s
Several other types of lamps are available in conjunction with high-performance T8s. One type of lamp is a reduced-wattage T8 lamp (for which the CEE has developed a reduced-wattage specification) and includes the 28- and 30-watt reduced-light-output or energy-saver T8s, some of which operate almost as efficiently as the 32-watt high-performance T8. In some retrofit applications, they provide an easy way to harvest energy and demand savings because they don’t require delamping or dealing with the expense of replacing ballasts or luminaires (figure 4). However, there are several limitations to their use (see How to make the best choice).
In addition to reduced-wattage products, many premium 32-watt T8 products offer extended lamp life or higher light output compared with standard 700- and 800-series CRI lamps. But, none of these perform as well as high-performance T8s.
T5 fluorescent lamps are available only in metric lengths and, therefore, aren’t a good retrofit option; however, they can be an effective choice in new construction or major renovations. Their efficacy is similar to that of T8 lamps, but their smaller size affords better optical control. The T5 lamp is currently designed for operation only on high-frequency, rapid-start, or programmed rapid-start electronic ballasts. T5 lamps also offer high lumen maintenance, putting out as much as 97% of their original light output at 40% of rated life. T5 lamps are designed for a high optimal operating temperature, which improves performance in enclosed fixtures and warm spaces.
High-output and very-high-output lamps
These lamps come in several different diameters. They offer very high luminous intensities, which makes them good for outdoor signage applications, particularly those that are backlit through colored materials or that operate during the day, such as convenience store signs, billboards, and roadway signs. However, both types require special ballasts and are less efficient, more expensive, and not available in as many color temperatures as standard-output lamps.
How to make the best choice
Buyers and specifiers face challenges in sorting through the confusing array of lamps and ballasts entering the market. Lighting manufacturers are competing for their share of the new, replacement, and retrofit markets by introducing a stream of innovative high-performance and not-so-high-performance T8 products that promise energy reductions, lower maintenance costs, and greater versatility. You have to scrutinize manufacturer product literature, performance specifications, and the fine print to sort out and benchmark the relative performance of these competing products.
When comparing high-performance T8s among themselves or to similar lamps and ballasts that aren’t necessarily in the high-performance category, be sure to examine the options equally.
Mean lamp lumens Output from all light sources decreases over time, and at different rates, which makes comparisons based on initial lumens misleading. Comparing by the “mean lamp lumens” that are listed in lamp catalogs is a better alternative. This value is the lumen output of a lamp after it has operated for 40% of its rated life.
CRI Measured on a scale of 0 to 100, CRI describes the ability of a light source to render a sample of eight standard colors relative to a reference source. A CRI of 100 means that the source renders the eight standard colors in exactly the same way that the reference light source renders them. CRI is an average value, so it won’t describe how a light source renders a specific color. However, high-CRI light sources render colors better than low-CRI sources. Most T8 products have CRIs in the 70s or 80s; T5 lamps offer CRIs in the 80s. The industry considers a CRI of 80 or greater to provide excellent color rendering.
Color temperature Measured in kelvins (K), this value indicates the sense of warmth or coolness that a light source gives to a space. The lower the color temperature, the warmer the light appears. Temperatures below 3,500 K are generally considered warm; those above 4,000 K are considered cool. Fluorescent lamps generally range from 3,000 K to about 4,100 K, although 2,700-, 5,000-, and 6,500-K temperatures are also available. (Daylight ranges from 5,000 to 10,000 K.) In some cases, light output varies with color temperature within the same lamp series. For example, the Sylvania XPS 4100K produces 45 mean lumens more than its 3500K and 3000K versions.
Lifetime, under a given duty cycle and ballast type Lifetime comparisons are meaningless if the duty cycles and ballast types aren’t identical. For example, Philips has made a major effort to reach 30,000-hour lifetimes with its Advantage product line at three hours per start on any ballast. But, in the low-wattage energy-saver lamps, the three major US companies have become cagier—one manufacturer reports lamp life using 12 hours per start to maintain the “20,000-hour” rating of its 30-watt product. This is misleading—the truth is that the longer any fluorescent lamp remains on, the longer its life will be.
When comparing performance among competing lamp-and-ballast systems, always reference the individual lamp-and-ballast criteria, and then perform a few key assessments:
- Pair up lamps and ballasts that are optimized to work as a system.
- Mix and match different lamp-and-ballast combinations to provide desired lumen levels and acceptable lamp lifetimes. Note that light levels will increase when you substitute normal ballast factor (BF) high-performance T8 ballasts for normal-BF standard T8 ballasts. To maintain the same light levels and achieve greater energy savings, the high-performance replacement ballast should have a lower BF.
- Compare systems rated for operation at the same ambient temperature (for example, in open air or enclosed fixtures). Otherwise, light output and power consumption might differ. Some ballast literature is especially helpful in that it provides watt ratings for open air as well as enclosed lamps.
When evaluating lamp options, also evaluate actual lighting needs to maximize savings—many spaces are overlit to some degree.
Highly overlit spaces Many older spaces are highly overlit according to current standards. Standard design light levels for many applications, such as offices and classrooms, have been reduced from the 200 to 150 foot-candles deemed acceptable in the 1960s down to 75 foot-candles by the 1990s, and then to 50 foot-candles in recent years. These kinds of spaces represent energy-saving gold mines, particularly using delamping strategies and upgrading to high-performance T8 lamps and ballasts that have the optimal BF for the space.
Slightly overlit spaces In many cases, you can design energy-saving retrofits to reduce light levels in spaces that are slightly overlit. This is an application where 30- or 28-watt reduced-wattage or energy-saver lamps might be a good choice when paired with a high-performance T8 ballast, saving an additional watt or two per lamp. Alternatively, you can save more energy by delamping the fixtures and retrofitting them with 32-watt high-performance T8 lamps paired with ballasts that have the appropriate BF to achieve the desired lighting level.
Properly lit spaces Replacing standard T8 lamps with 32-watt, high-performance T8 lamps and low-BF ballasts can deliver savings of at least 6 watts per lamp while maintaining existing light levels. Replacing T12s with high-performance T8s, lamp-for-lamp, can save even more.
Keep in mind that T8 lamps labeled “energy-saver” and “reduced-wattage” can provide energy savings but suffer from some operational restrictions. Depending on the product, they aren’t recommended where ambient temperatures fall below 60° Fahrenheit; in drafty locations; or for use with low-BF ballasts, rapid-start ballasts, dimming ballasts, or occupancy sensors. Some even require a brand-specific ballast to operate properly.
Another limitation is that people typically don’t want to maintain two different types of lamp systems—one for unconditioned spaces or spaces where dimming might be used, and reduced-wattage systems for other uses. That’s because it can be hard for maintenance crews to keep track of the different lamp types. As one lighting retrofit expert points out, it’s difficult enough to keep track of where to install T8 and T12 lamps, which have different diameters, and even harder for workers to keep straight the multiple types of T8s, which look very much the same.
Reflectors are specially shaped retrofittable metal sheets designed to improve the efficiency and light distribution of conventional white-painted, ceiling-mounted fluorescent downlight fixtures (figure 5). With higher reflectivity and more directional control than the white paint on many existing fixtures, reflectors can significantly decrease the internal losses of fixtures and improve light distribution.
Well-designed reflectors improve fixture efficiency enough to allow some delamping. Although manufacturers frequently claim that the use of reflectors will allow 50% delamping with little or no reduction in the fixture’s light output, that goal is difficult to achieve—it’s more about the quality of the fixture than the effectiveness of the reflector. In any application, you should consider delamping carefully, bearing in mind that it may also be possible to delamp without a reflector.
Because there’s a large population of existing 2 x 4 fixtures with four 4-foot lamps, it’s common to remove two of these lamps. This can be a realistic goal if one or more of the following conditions are met:
- The space is measurably overlit; otherwise, a reduction in light level won’t be noticeable.
- The existing fixture efficiency is extremely poor and can’t be corrected by cleaning or lens replacement.
- A proposed reflector will provide better light distribution, allowing more-uniform illumination at a lower light level.
- Replacement of the lamp-and-ballast combination increases the average light output per lamp.
- A better lens, diffuser, or louver is also installed.
- The existing lamps were close together, raising their average temperature while shading each other.
Spot versus group relamping
There are four main reasons to practice group relamping (a set of lamps is replaced at a scheduled time) rather than spot relamping (lamps are only replaced when they burn out):
- It requires less labor per lamp than spot relamping. A worker might take as long as a half hour to retrieve and install a single lamp. If all the materials were on hand for a large number of lamps, a worker could move systematically from fixture to fixture and cut the required time to about three minutes per lamp. The process would also be less disruptive because group relamping is usually done outside working hours.
- It’s easy to schedule and delegate. Only outside contractors who have special equipment and training can do the work.
- It provides brighter and more-uniform lighting. Because lamps are replaced before their output has fully depreciated, lighting remains consistent. Direct energy benefits result if the designer, anticipating group relamping, uses a smaller safety factor.
- It increases control over replacements. It’s much more difficult to mix incompatible lamps—such as those with different color temperatures—when all of them are changed out at once.
Economic comparisons typically show that group relamping has higher lamp costs but lower labor costs than spot relamping. One such comparison in figure 6 indicates a 31% overall savings from group relamping. This type of calculation is heavily dependent on the difference in labor costs between group and spot relamping. For example, if the group relamping cost of $1.50 per lamp jumps to $3.50, the balance tips in favor of spot relamping. Keep in mind the noneconomic benefits of group relamping when deciding between the two methods.
What’s on the horizon?
Fluorescent lamps are a mature technology, but manufacturers continue to make incremental improvements in efficiency and lamp life. The latest development is the use of mercury amalgams in full-size fluorescent lamps to reduce the sensitivity of lamp output to temperature change. In another trend, manufacturers are introducing lamps that carry a small penalty in efficacy to provide a larger increase in lamp life.
Who are the manufacturers?
The list below presents some of the leading manufacturers of fluorescent lamps.
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