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Saving Energy With Proper Fluorescent Lighting

Regulatory pressures and the global move toward reduction in unnecessary energy use continue to push energy conservation in virtually every sector of the economy.In the past few years, electric utility companies have used demand side management programs to reduce electric energy demand. As part of the overall strategy, they applied incentives in the form of energy rebates. In many cases, utilities

Regulatory pressures and the global move toward reduction in unnecessary energy use continue to push energy conservation in virtually every sector of the economy.

In the past few years, electric utility companies have used demand side management programs to reduce electric energy demand. As part of the overall strategy, they applied incentives in the form of energy rebates. In many cases, utilities worked in conjunction with contractors to recommend products and value-added services to commercial and industrial customers.

At this time, retrofit projects continue to happen despite the reduction in utility incentives and energy rebates. It is not necessary for energy users to wait and see if utility deregulation will lower rates enough before doing a lighting retrofit. You can finance many retrofits in such a way that the energy savings more than pays for the cost of the new lighting system. In some cases, the building owner can even enjoy a positive cash flow.

Electrical contractors can take heart from this news. You can still make money by proposing viable retrofits. Let's look at fluorescent lighting systems. Specifically, it is worthwhile reviewing fluorescent lighting technology because of recent improvements in both lamps and ballast components.

The standard T12 40W lamp, used in the industry since the inception of the fluorescent lamp, has given ground to the 32W T8, high color rendering index (CRI) lamp. And the T8 lamp gains its highest performance when served by an electronic ballast (EB), which offers substantial improvements in performance and reliability, compared with the 60-Hz operation of a core and coil magnetic ballast.

Another important characteristic of an EB is the ability to serve the lamps at various light outputs. Ballast factor (BF) achieves this. BF is the percentage of lumens from a lamp operated by the actual ballast compared with the lumens from the same lamp type operating with a test bench or laboratory standard ballast. Thus, an EB can have a low (around 70%), normal (around 85% to 95%), or high (above 100%) ballast factor. Here are the details: * Partial-output electronic ballasts. Low or partial output EBs are useful when you desire reduced illumination, such as a computer-intensive office where delamping (which is simply the removal of one or more lamps) of existing fixtures achieves the 20 to 30 footcandles recommended for the ambient component of a task/ambient lighting system. Thus, while delamping alone can result in uneven luminaire brightness, a reduced-output electronic ballast can provide uniform reduced luminaire brightness across the entire luminaire aperture and also deliver the appropriate amount of illumination on task surfaces. * Full output electronic ballasts. In nearly every fluorescent lighting system, a full-output electronic ballast can replace a core and coil magnetic ballast. Where feasible, the use of three- and four-lamp ballasts instead of two-lamp ballasts can save money (material, labor, and energy costs). In applications with two-lamp luminaires, consider tandem-wiring a pair of two-lamp luminaires to share a single four-lamp ballast. In this situation, find out what the manufacturer recommends as the maximum lead length between the lamp sockets and ballast for reliable operation.

Keep in mind many T8 electronic ballasts have unique wiring diagrams. Become familiar with the wiring diagram for a brand you are using for the first time; this will prevent the possibility of problems later.

In 1994, a performance standard for electronic ballasts, ANSI C82.11-1993, High Frequency Fluorescent Lamp Ballasts, was issued. This standard established, as a maximum value, a 32% total harmonic distortion (THD). Most of the electronic ballasts used today have a 20% THD, although some products are available with a THD in the range of 5%. While this low harmonic level has no effect on the power consumed, it may have a very positive effect within the power system since this reduces the total harmonics present.

Other ballast choices Since not every project requires the use of electronic ballasts, contractors should also consider the application of hybrid magnetic ballasts. Also called a cathode disconnect ballast, this unit is a standard magnetic ballast that removes power to the cathode heater circuits (the lamp filaments) after the fluorescent lamps are lit. This results in an additional 2W savings per lamp during operation. This type of ballast, which is about $4 less expensive than an EB, is suitable for all two-lamp ballast applications with 4-ft T8, T10, or T12 rapid-start fluorescent lamps.

In a room or space where electromagnetic interference (EMI) from an EB is a potential problem (proximity to sensitive electronic equipment) the hybrid magnetic ballast-with a slightly lower EMI-should be considered. You should not use the hybrid ballast, which is available as either a full-output or partial-output model, in any dimming application or with 32W heater cutout type lamps.

Upgrading commercial lighting systems When owners face the prospect of upgrading a commercial lighting system, they can follow either of two approaches: * Remove old fixtures and replace them with new fixtures that better serve the application, such as a direct/indirect luminaire type. * Retrofit the old fixtures with new ballasts (lamps) and perhaps lenses.

Retrofitting an existing luminaire can involve delamping accompanied by the use of higher output lamps, a reflector, and the cleaning of the luminaire interior surface.

While the number of lamps removed directly determines light level reduction, there is also another factor to consider. In an enclosed luminaire, de-lamping will bring a 5% to 10% increase in efficacy (lumens per watt), because the lamps operate cooler within the enclosure, and there are fewer lamps to block the total lumen output of the fixture.

Delamping may not be suitable for series-wired, two-lamp luminaires where the removal of one lamp extinguishes the other. In such cases, consider installing a partial-output (low ballast factor) electronic ballast to operate both lamps at reduced wattage and reduced output.

Several new lens patterns developed in the past 10 years improve appearance ...when you delamp fixtures in overlit spaces. Such reductions in light levels also further accentuate uneven light levels, so these lenses "fill in" dark areas at task level by more widely distributing the light, while "hiding" the shadows in fixtures where lamps are removed. Other lenses cut VDT screen glare by narrowing beam spread in one plane (oriented perpendicular to the screens) while widening it in the other, filling in potential dark areas to the sides of VDT operators.

These asymmetrical distribution flat lenses have proven useful during lighting upgrades and for new fixtures equipped with special reflector designs. Specular reflectors, for example, can make lighting fixtures appear more glary (even when they do not change the spacing to mounting height), but adding such a widespread lens can reduce the fixture's apparent brightness while distributing light more evenly.

Two more accessory products are available for both existing and new fixtures. Developed to allow re-use of existing (but poorly spaced) fluorescent pendant fixtures, a specular reflector with widespread distribution along with a lamp socket relocation device raises the spacing to mounting height (S/MH) ratio of a fixture from the usual 1:2 up to 1:5.

The second product is a lens that looks like an upside-down pyramid stretched along one axis. The lens has up to 40% more surface area than a flat lens of the same width. The ends of the lens also angle to alter the light distribution.

A basement hallway used for locker storage is an application suited for these two products. The existing two-lamp recessed one-by-four fixtures were up to 18 ft apart in a 10-ft ceiling, delivering a 6:1 ratio of illumination, when measured at floor level under and between fixtures.

A widespread specular reflector was added dropping the light level ratio to about 2:1, thus greatly reducing the horizontal fc variations. When the pyramid lens was added, the ratio of illumination was further reduced to a desirable 1:1.

Economical dimming of fluorescent lamps. Saving energy with dimmable ballasts requires careful coordination and proper equipment selection.

Dimming control options - Controllable electronic fluorescent ballasts vary the light output based on a signal from an external device.

The 10-0VDC control system is rapidly becoming the industry standard for continuous dimming of T8 fluorescent lamps from 100% to 20% output, and these ballasts are available presently only in the two-lamp configuration. Because these latest dimming ballasts are quite cost-effective, their applications are expanding. At 20% of full light output (maximum dimming), the system efficacy drops from about 84 lumens per watt (LPW) to about 58 LPW. Note that a 70% reduction in power consumption accompanies this 80% reduction in light output. Systems that dim down to a 1% light level are more expensive.

The external control device can be a manual wallbox control, photoelectric light sensor, occupancy sensor, or system controller. All of these control devices send a low-voltage signal to the ballast using two control input leads, one with violet color; the other with gray color to the conductor insulation. When more than one device is controlling the ballast output (for example, a photosensor and an occupancy sensor), you can use an integrated load controller to determine the appropriate signal to send to the ballast.

A dimming ballast achieves maximum lamp life by controlling minimum lamp current, lamp starting, cathode voltage, and lamp current crest factor (LCCF). LCCF is the ratio of peak lamp current to RMS lamp current. The American National Standards Institute (ANSI) recommends less than a 1.7 LCCF for T8 lamps.

Many buildings have started using occupancy sensor and timers to turn lights off in areas of intermittent occupancy, such as corridors, stairs, library stacks, and rest rooms. At the outset, engineers and designers debated whether instant-start or rapid-start electronic ballasts were better to use with these control devices. Studies indicate instant-start ballasts will provide maximum energy savings, but rapid-start ballasts are the economical choice when the lighting loads are turned on and off frequently. Because this choice is concerned with shortened lamp life caused by frequent lamp starts, using either a stepped ballast (50% output) or 20% to 100% variable ballast would also be appropriate.

Selling successful retrofits to upper management is not only important, it is critical. But before starting the process, prepare the following: * Expertise: Become as skilled in energy-saving lighting as you and your firm are in general electrical installation. * Training: Learn about technologies that will provide the best strategy. *Time: Several presentations on design and modifications may be necessary before you conclude the sale, so be prepared to devote sufficient time to the effort.

Suggested Reading EC&M books: Practical Guide to Electrical Energy Efficiency & Reduced Costs; Order #5844. Practical Guide to Modern Lighting Techniques; Order #4783 For ordering information, call (800) 543-7771.

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