Energy-efficient lighting designs offer new features and technological capabilities
Creative and innovative new products in both the lamp and ballast markets continue to transform the lighting industry, enabling specifiers and users to translate “energy-effective lighting” into concrete savings and enhanced illumination designs. As the technology continues to evolve, it's a good idea to keep abreast of what's new and on the horizon.
Long live fluorescents.
New barrier coatings reduce the amount of mercury in linear T8 fluorescent lamps, while also allowing manufacturers to use a thinner phosphor coat. Phosphor coating improvements make it possible to get the same amount of light with lower wattage or even squeeze more light from the same wattage.
These technology boosts for fluorescent lamps greatly expand the selection. For example, second generation 800 series F32 T8 lamps with matching ballasts are rated for 24,000 hr with 92% lumen maintenance. One manufacturer's T8 lamp offers full rated life on all T8 ballast systems used with this line of lamps, and promotes 33% longer life on instant-start ballasts than standard T8 lamps.
New ballast designs matched with specific linear fluorescent lamps also offer optimum performance. At least two manufacturers offer 4-ft T8 extended performance lamps rated at 3,150 lumens. The new designs combine a low ballast factor (0.74), low-input wattage, and programmed rapid starting to maximize energy savings and lamp life.
The T5 fluorescent lamp, in nominal lengths of 22 in., 34 in., 46 in., and 56 in., is showing up in more pendant-mounted linear fixtures used in commercial and institutional spaces. Although the lumen per watt output isn't a significant improvement over T8 lamps with electronic ballasts, the 0.625-in. diameter T5 lamp provides markedly improved control and optical efficiency for both direct and indirect luminaires. In a 46-in. long lamp, a specifier can select either the standard 28W T5 or the high-output (HO) 54W line.
Dimming ballasts for T5HO and other lamp types are becoming more readily available, allowing lighting architects to use daylight harvesting in conjunction with skylights and other peak load shedding strategies.
Improvements in compact fluorescent lamp design like high temperature components result in longer life and higher wattage offerings. Ratings of 70W, 80W, and even 120W, and light outputs of as many as 9,000 lumens, allow these new lamp models to be used in high-ceiling or high-light-level applications, thus competing with metal halide sources.
Effective April 1, 2005, the U.S. Department of Energy will raise the ballast efficiency factor (BEF) from levels met by the current energy-efficient T12 ballast to those met only by the electronic T12 ballast. However, considering several of the associated economic factors, users should consider T8 electronic ballast systems as the standard of the future, rather than even considering T12 electronic ballast systems.
The newest T8 electronic ballast designs have features like end-of-life sensing and automatic shut off, and the ability to “soft start” a fluorescent lamp to extend lamp life. Four types of electronic ballasts for linear T8 fluorescent lamps are currently available:
The instant-start ballast is the most widely used today because it costs the least. Since it doesn't provide lamp electrode heating, an instant-start ballast consumes 1.5W to 2W less energy per lamp than a comparable rapid-start ballast. Typically, lamps on instant-start ballasts withstand 10,000 to 15,000 switch cycles.
The rapid-start (RS) ballast has a separate set of windings that provide about 3.5V to heat the lamp cathodes for one second prior to lamp ignition. This is the same starting system used with the T12 lamp. This ballast typically provides as many as 20,000 lamp starts. An RS ballast is wired in series, so if one lamp fails, the other lamps in the circuit are extinguished.
The program rapid-start (PRS) ballast is designed for use with occupancy sensors and can provide 30,000 starts. The PRS ballast heats the cathodes to 650°C before applying arc voltage to the lamp. Usually wired in series, some PRS ballasts also feature series-parallel lamp operation for 3- and 4-lamp fixtures.
The programmed-start (PS) ballast provides as many as 50,000 starts, making it the best choice for frequently switched circuits. The PS ballast heats the cathodes to 700°C before applying arc voltage to the lamps, which are usually wired in series.
Various electronic ballasts offer other useful features, such as economical dimming and multi-level operation.
In the near future, however, the selection of a fluorescent ballast will be much simpler, as manufacturers plan to produce only instant-start and PS T8 ballasts. Look for universal input voltage (108V to 305V), end-of-life sensing, and less than 10% THD on most new models.
Who needs an electrode anyway?
For many years, lighting manufacturers have tried to eliminate electrodes in lamp operation because the emission coating on the electrodes at each end of a linear lamp deplete over time, which is a major cause of lamp failure and a barrier to longer lamp life.
Inductively coupled electrodeless fluorescent lamps that last as many as 100,000 hr are appearing more frequently on bridges, tunnels, high-mounted street luminaires, and similar difficult-to-reach locations. These new lamp types use high-frequency energy to activate the mercury plasma gas and thus the phosphor coating on the lamp's interior surface. This allows the electrodeless lamp to restart immediately after a momentary loss of power. These lamps maintain operating stability in very cold temperatures, provide constant light output regardless of supply voltage fluctuations, and offer no shift in color over life.
Another type of induction lamp currently available for purchase is known as a re-entrant cavity induction lamp, which is available in 55W, 85W, and 165W models that provide 3,500 lumens, 6,000 lumens, and 12,000 lumens, respectively. All models are shaped like an oversized standard incandescent A lamp. This lighting system has three separate components: the high-frequency current generator that operates at 2.65 MHz, the power coupler that consists of an induction coil wound on a ferrite core, and the lamp compartment, which consists of the glass bulb equipped with an internal phosphor coating and a base. A short coaxial cable delivers power from the radio frequency generator to the base of the lamp.
LEDs look to the future
When it comes to energy efficiency and long life, light-emitting diodes (LEDs) appear to be promising, having already made headway in niche lighting applications like architectural and stage lighting.
An LED produces light by forcing together positive and negative electrical charge carriers in a very small region where two different types of semiconductor materials meet. When current flows across the junction of the two semiconductor materials, light is produced from within the solid crystal chip. Attractive characteristics include relatively high efficacy, reasonably long life, small size, rugged construction, fast on (60 nsec. vs. 10 msec. for incandescent), ease of dimming and control, and low-voltage operation.
Material composition determines the wavelength and color of light. While red, green, and amber LEDs have been available for decades, the invention of the gallium nitride (GaN) LED, which produces white light, represented an important milestone. Today, the world's brightest LED product is a 5W unit that produces 120 lumens of directional white light from a very small package. A 250-lumen LED should be available within two years. Another common approach used to produce white light is to put a blue LED chip beneath a film of yttrium-aluminum garnet (YAG) phosphor. The phosphor gives off yellow light when struck by the blue light and the resulting mix of the two colors actually appears white.
However, before solid-state lighting systems can move into task and perhaps general lighting, a number of obstacles must be overcome, such as a reduction in cost and improvement in color rendering and color temperatures.
The incredible shrinking metal halide lamp.
The standard wide-body metal halide (MH) lamp is giving way to the smaller “bulgy” arc tube MH lamp. Shrinking the arc tube and changing its shape provides better control of the metallic salts within the unit. Because the arc tube has no room to accommodate the probe electrode found in the standard MH arc tube, it uses a high-voltage pulse-to-start arc conduction, similar to the technology used in an HPS lamp.
Depending on other factors like wattage, a pulse-start MH lamp may offer either substantially lower energy costs with equal or better light levels compared to a wide-body, probe-start MH lamp, or a substantially higher light level per watt with moderate energy savings. In addition to improved lumen maintenance, the pulse-start lamp also offers a faster restrike time if the arc is interrupted while the lamp is hot and improved color uniformity over the older probe-start MH lamp. In many cases, a 320W or 350W pulse-start lamp can directly replace a 400W standard MH lamp, or fewer 400W or 450W pulse-start MH fixtures can be used in a lighting layout.
The TC lamp, the newest and smallest member of the MH family, can create more versatile and compact luminaires. Only 3.35 in. long, 3,300-lumen and 6,400-lumen lamps fit inside a variety of fixtures, producing precision beam patterns and adjustable beams in some cases.
The same power-handling electronics used in fluorescent ballasts are also being used increasingly in metal-halide ballasts to provide longer lamp life, end-of-life sensing, color stability and dimming capability in the lower wattage range.
With energy savings still on most facilities managers' and building owners' minds, lighting manufacturers continue to develop better and more energy-efficient lighting technologies. And now as initial cost continues to fall, it's becoming more and more difficult to find excuses not to upgrade.