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What Are the Options?
There are two basic categories of full-size fluorescent ballasts (Figure 1 shows both types). Magnetic ballasts provide output power to the lamp at line frequency (60 cycles per second in North America and 50 cycles per second in many other regions of the world). Electronic ballasts use semiconductor technology to convert incoming 60-cycle power to drive the lamps with high-frequency current of 20,000 cycles per second or more. Electronic ballasts are more efficient in a number of ways. Most notably, they waste less power internally than magnetic ballasts, saving 3 to 8 watts per ballast. Their higher frequency drives lamps about 10 percent more efficiently than do 60-cycle magnetic ballasts. And those electronic ballasts with dimming capability save energy in multiple ways, from lumen compensation that eliminates the need to overlight spaces when the lamps are new to the tens of percentage points in savings that come from reducing electric light levels when daylight is available. Some well-publicized failures of certain early-generation electronic ballasts made users wary of the technology's reliability. Over the past decade, however, manufacturers have worked hard to dispel these concerns, with a combination of improved design and higher quality control standards in components and assembly. Today, electronic ballasts from established suppliers are just as reliable, if not more so, than magnetic ballasts. Until 1991, the dominant ballast available in the U.S. was the standard efficiency magnetic ballast. Hundreds of millions of these ballasts are still operating in U.S. buildings, typically driving standard-efficiency T12 fluorescent lamps. In 1991 federal energy efficiency standards went into effect in the U.S. that banned the manufacture and sale of standard magnetic ballasts. Since then, only energy efficient magnetic ballasts (about 10 percent more efficient than standard magnetics) and electronic ballasts (more efficient than even the best magnetic units) have been available. How to Make the Best Choice Ballasts are often the most expensive first-cost component of a lighting retrofit. Energy efficient magnetic ballasts typically cost $12 to $20 each, in volumes of 1,000 units. Nondimming electronic ballasts typically cost $14 to $30 each, and dimming models are priced from the low $30s to more than $50 each. Remember to consider lifecycle cost (including energy cost savings) as well as first cost when making your choice.
Beyond the basic split between energy efficient magnetics and electronics, a dizzying array of other performance criteria distinguish ballasts:
Users should consult with a qualified lighting designer, but the following general guidelines can apply in many instances: High-frequency electronic ballasts with T8 lamps are typically the most efficient solution with the lowest lifecycle cost. There are some situations, however, in which it makes sense to use magnetic ballasts. These include settings where the equipment will operate in extremely hot or cold conditions and locations where there is a lot of sensitive electronic equipment. Electronic ballasts have been known to interfere with book detection systems in libraries, inventory security systems in stores, recording studio equipment, and some electronic medical equipment. Because they operate at much lower frequency, magnetic ballasts do not cause such interference and may be a safer choice in such settings. Instant-start ballasts are appropriate for applications in which lights will be left on for more than three hours at a time. For shorter-duty-cycle applications, including settings with occupancy sensors, the new family of programmed-start ballasts should be considered. Weigh the higher first cost of the programmed-start ballasts against the fact that lamps will last longer with them than when operated on instant-start ballasts. With the advent of programmed-start ballasts, rapid-start designs, which used to be the ballast of choice for short-duty-cycle applications, are rarely called for.
What's on the Horizon? Lighting designers have long been awaiting the emergence of low-cost, reliable, high-performance dimming electronic ballasts. That wish is closer to being realized, as several dozen models are now available and prices are dropping into the low $30 range for two-lamp dimming ballasts. Dimming ballasts can enable such strategies as automatic daylight dimming, lumen maintenance (automatically adjusting ballast power to compensate for the gradual loss of light output as fluorescent lamps age), occupancy-controlled and -scheduled dimming, and manual task dimming that gives occupants precise control over the light levels in their area. Dimming ballasts can also enable lighting loads to be minimized during periods of high electricity prices or to help facilities minimize demand charges. Who Are the Manufacturers? A list of leading fluorescent ballast manufacturers follows. Dozens of firms produce ballasts; for a more complete listing see lightsearch. (Neither this list, nor any mention of a specific vendor or product in this guide, constitutes an endorsement or recommendation of any vendor or product by E Source, Inc., nor does this guide constitute an endorsement or recommendation, explicit or otherwise, of your service providers' various technology-related programs.)
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