Taking Energy Efficiency To New Heights Washington DC

Recent lighting technology improvements have increased overall system performance for high-bay lighting systems, making it possible to reduce energy bills, improve light quality and enhance overall operating results.

High-bay lighting is used when ceiling height is greater than 20 feet and is often used in industrial and warehouse applications. These applications traditionally use metal halide for the high wattage availability and high lumen ratings to achieve cost-effective lighting using a minimal fixture count. However, new high-efficiency linear fluorescent lamps are now useful in high ceiling applications.

Lighting design for industrial and warehouse applications are based on several factors, including safety, energy cost, maintenance cost, quality of light and lighting uniformity. Depending on the lighting application, these considerations may not factor into the lighting design process equally.

For example, an industrial environment that is responsible for inspecting colored textiles may require either good color rendering from a general lighting source or supplemental task lighting with the proper color quality. A source with a lower color rendering index (CRI) may suffice for a warehouse application where seeing true colors is not important. Each design factor contributes to a facility's overall operating results.

Cost reduction and cost avoidance are achieved in several ways. Long-life light sources reduce maintenance costs and cause fewer work interruptions. Uniform light levels with good color quality may improve plant productivity, reduce lost-time accidents, increase worker morale and improve a facility's image. Energy-efficient lighting affects energy costs. These attributes can improve operating results.

Task lighting and lower ceilings

Most industrial or warehouse facilities use high intensity discharge (HID) for higher ceilings and fluorescent lighting for lower ceilings and task lighting. In many cases, task lighting scattered throughout a facility increases or improves the lighting in specific small areas that require different lighting than provided by the general lighting. For lower ceiling and task lighting applications, T8 fluorescent lamps on electronic ballasts have been show to improve lighting efficacy and quality over T12 fluorescent lamps. Table 1 shows the energy efficiency improvements of T8 lamps on electronic ballasts as compared to T12 lamps on magnetic ballasts.

The last column represents a 28W T8 energy-saving retrofit lamp. It operates on existing instant-start T8 electronic ballasts as a direct retrofit for standard T8 lamps. It saves approximately 3W per lamp over a standard T8, while providing slightly higher lumen levels. At 10 cents per kWh, the 3W per lamp results in $7.20 in energy savings over its life. In recent years, other higher output, energy efficient, longer life T8 lamp and electronic ballast systems have been introduced. For further information about energy efficient T8 fluorescent systems, contact a lighting engineer or energy service company.

High-pressure sodium lamps

High-pressure sodium (HPS) lamp systems have long-life ratings and a high lumen per watt rating, but have a yellowish color. Most HPS lamps have a color rendering index of approximately 22 on a scale of 100, which prevents accurate object identification on the basis of color alone. For this reason, HPS lamps generally have been relegated to outdoor area lighting or warehouse space where color identification is irrelevant.

Metal halide retrofit lamps

Metal halide lighting offers long life, good color rendering, good efficacy and consistent performance at any temperature. Two product families offer improved lamp efficacy. The simplest is the energy-saving retrofit, such as 360W metal halide lamps that operate in standard 400W M59 fixtures.

These lamps have life and lumen ratings equivalent to standard 400W MH lamps, but operate with a 40W savings. The first cost for a conversion to 360W units includes only the lamp, as no fixture or ballast changes are required. At 10 cents per kWh, energy savings over standard 400W metal halide lamps equates to $80 per lamp over the 20,000-hour lamp life.

Metal halide pulse start lamps

Higher wattage pulse start metal halide lamps were introduced in the mid 1990s. Lamp and ballast design changes reduce lumen depreciation, which gives lower-wattage lamps mid-life and end-of-life lumens similar to higher-wattage lamps. Because pulse-start metal halide lamps operate on different ballasts than standard metal halide lamps, they are not a true retrofit product. It often makes more economic sense to replace entire fixtures with a lower-wattage pulse start systems and a more efficient luminaire to maximize system performance using a lower-wattage lamp.

Major lamp manufacturers are testing high frequency electronic ballasts for use with pulse start metal halide lamps. Preliminary results promise even greater improvement in lamp life and efficacy.

Multi-lamp fluorescent systems

High-bay lighting systems using multi-lamp fluorescent lamps and high-efficiency luminaries also offer energy-saving improvements. Multi-lamp fluorescent fixtures often are more expensive then HID fixtures, but long-term efficacy and occupancy sensors can make them more cost-effective in the long run.

New fluorescent lamps offer good-to-excellent CRI, dimming flexibility, long life and excellent lumen maintenance. Their nearly instant-on and instant hot restrike capability make them suitable for many traditional HID applications. Where long operating cycles (10 to 12 hours per start or more) are encountered, the T8 and T5HO lamps provide substantial longer life than other options.

Table 2 details data for the most common high-bay lighting systems. In each case, lower wattage pulse start metal halide systems and multi-lamp fluorescent systems have low initial lumens than the 400W metal halide system. However, the maintained lumens will be equivalent.

Several important points apply to Table 2. First, the baseline used was an inefficient 400W metal halide system. There are more efficient metal halide lamps and fixtures available, but they are rarely used in older installations. Second, the table assumes converting to a lower-wattage pulse start metal halide system would involve changing to more efficient luminaries. Third, lamp life ratings are not identical for every system. For example, the 42W compact lamps have a life rating of 12,000 hours. Most other types on the chart have a lamp life rating of 20,000 hours. Fourth, the T5 fixture efficiencies of near 100 percent are achievable because only T5 lamps operate at higher efficacies inside the warmer fixture than in open air.

Manufacturers generally publish lumen ratings for T5 lamps at 25° C and 35° C. The high fixture efficiencies of near 100 percent are the result of using the lower rated lamp lumens at 25° C ambient. One cannot make a fair and accurate system comparison by using the higher lumen rating of T5 (at 35° C ambient) and near the 100 percent fixture efficiencies published by the luminaire manufacturers. Finally, the luminaire efficiencies and lamp lumens in Table 2 are typical values. The exact values vary accounting to manufacturer, so it pays to consult the published literature for more accurate information.

Metal halide and fluorescent systems offer energy savings potential, but Table 2 doesn't tell the entire story. Cold storages areas or unheated spaces may require the most energy-efficient metal halide systems with its stable, temperature insensitive light output and efficacy, although new developments in amalgam technology are significantly reducing this effect. Conversely, a fluorescent system would be preferable for installations with occupancy sensors used to reduce energy use.

Metal halide lamps can be dimmed to 50 percent power, but they can't be shut off with occupancy sensors. Once extinguished completely, metal halide lamps require five to 12 minutes to cool down and restart. Furthermore, once ignited, it may take one to three minutes to achieve full output. Fluorescent lamps are instant on and instant restrike, making them suitable for use with occupancy sensors.

Improvements in metal halide, compact fluorescent, T8 and T5 linear fluorescent lighting electronic ballasts, and luminaries have presented opportunities for upgrades to save energy. In some cases, payback can be less than one year. In most cases, it's less than three years. Contact a lighting engineer for a complete list of energy-efficient lighting options.

Bob Ponzini is a commercial engineer at Osram Sylvania. Jeff Waymouth is a senior applications engineer — fluorescent at Osram Sylvania.