High/Low-Bay Applications: Fluorescent or Metal Halide?

By Craig DiLouie, Lighting Controls Association

Published November 2004

Indoor spaces with high ceilings, such as factories, warehouses, big box retail stores, gymnasiums and all-purpose rooms are most often lighted by high-intensity discharge (HID) lighting systems.

Recently, manufacturers have begun offering specialized T8 and T5HO fluorescent fixtures as an alternative for high-ceiling applications. These fixtures provide distinct advantages versus HID fixtures. Traditionally, fluorescent lighting has dominated the <15 ft. ceiling height niche, but new technology has enabled it to be competitive with HID in higher ceiling heights, even over 25 ft.

Figure 1. Fluorescent lighting provides distinct advantages over HID lighting in applications with high fixture mounting heights; new lamp technology enables fluorescent to be competitive with HID at fixture heights as high as 35 ft. Courtesy: Sacramento Municipal Utility District (SMUD).

Manufacturers offer new fluorescent fixtures that can be substituted for HID for relighting/upgrade as well as renovation and new construction projects. The market potential is significant. However, relighting projects typically require installation of new fixtures, which can inflate payback periods and reduce return on investment.

A second alternative to standard HID is pulse-start metal halide, which provides superior performance and, depending on the ballast, dimming capability. The right choice, as with all things in lighting, depends not just on economics, but on what capabilities the owner needs in their lighting system.

In this special report from the Lighting Controls Association, we will examine the advantages and disadvantages of fluorescent and metal halide in applications with high fixture mounting heights.

Ceiling heights
In the lighting industry, we often hear talk of “high bay” (also called hi-bay) and “low bay” (lo-bay) lighting. What does this mean?

In the construction of some types of industrial facilities, a skeletal framework is used, which forms an interior subspace called a “bay,” which in turn marks the space as “high bay” or “low bay.”

An older definition designated high-bay to mean >25 ft. off the floor, medium-bay to mean 15-25 ft., and low-bay to mean <15 ft.

Some manufacturers define high-bay as being over 15 ft. or 20 ft. off the floor.

The Illuminating Engineering Society of North America (IESNA), the authority in lighting, categorizes spaces as either high-bay (>25 ft.) or low bay ( <25 ft.).

The terms “hi-bay” and “lo-bay” also refer to fixtures designed for these applications, although it is not uncommon to see hi-bay fixtures in low-bay applications, and vice versa.

Metal halide: standard choice for many high/low bay applications
Metal halide is the dominant light source in many high-ceiling applications in warehouses, industrial buildings, gymnasiums, all-purpose rooms and big-box retail stores. At higher ceiling heights, 250W and 400W sizes are common. High pressure sodium lamps are also popular; for this article, however, we will focus on metal halide.

In review, the core operating components of a typical metal halide lamp include three electrodes within an arc tube that contains mercury and other metals in iodide form. One electrode is used for starting, and two for operating. The arc tube is constructed to withstand the internal high temperature and stresses of HID lamp operation. The tube is enclosed in a borosilicate glass bulb that is also highly heat resistant. These lamps are called probe-start metal halide lamps, or simply metal halide lamps.

These lamps are compact, rugged, powerful point sources. They produce enough light to cover a large space with few fixtures. A 400W standard metal halide lamp, for example, produces 36,000 initial lumens. Some standard metal halide lamps are rated as high as 41,000 lumens. They’re also efficient and provide good service life. At 10 hours/start, the service life of a 400W metal halide lamp is rated at 20,000 hours.

Compared to fluorescent, metal halide lamps have several distinct advantages. Metal halide is a powerful light source offering high lumen packages, and, depending on the application, can present a lower installed cost due to fewer fixtures. They are able to operate reliably in a wide range of ambient temperatures, including very cold environments, where fluorescent performance can be dramatically impaired (except for induction lighting, which is considered part of the fluorescent family). And numerous models are available that are specially designed for a wide range of demanding environments such as hazardous locations.

Despite their advantages, standard metal halide systems do not include any dimming capability, experience color shift over time, require four minutes to start, and require about 10 minutes for re-strike after shut-off. Most significantly, at 40% of service life, light output and efficacy experience severe degradation. A 400W metal halide lamp, for example, may produce 36,000 lumens but 25,000 at 40% of life, a 30% decline. Therefore, unless the lamps are periodically group-relamped, a large system’s “average” performance over time is much lower than its initial ratings.

Pulse-start metal halide
Before entertaining a challenge to metal halide by fluorescent, we should consider pulse-start metal halide as an alternative to standard metal halide. Pulse-start technology has been used in low-wattage metal halide lamps for decades, and has recently begun being used in higher-wattage lamps up to 1000W.

“Pulse-start metal halide has so many advantages over standard metal halide that the latter should get a fond farewell and gracefully retire,” says Stan Walerczyk, LC, principal of Lighting Wizards, a consulting firm. “It is a shame how many new standard metal halide hi-bays are still being installed.”

(He adds, “Some lamp manufacturers salespeople try to push the 360W energy-saving standard metal halide lamps to replace 400W standard metal halide lamps on existing ballasts, because it can be a quick sale, and a contractor is not necessary. Except for short-term leases, I usually find better solutions.”)

In a pulse-start metal halide lamp, the number of electrodes is decreased from three (probe start) to two, while a high-voltage ignitor is added that provides 3-4 kV pulses to ionize the gas and produce the glow discharge. Pulse-start metal halide lamps produce higher light output, enjoy higher lumen maintenance, are more energy-efficient (15% more efficient), produce a whiter light, and re-strike faster after an outage.

However, pulse-start lamps cannot be used with standard magnetic ballasts, instead requiring the installation of a compatible pulse-start ballast.

Table 1. Pulse-start metal halide performance. Source: Bonneville Power Administration.

*Efficacies as high as 107 lm/W (initial) and 86 lm/W (mean) are possible with 1000W lamps.

Below we see a basic comparison of a 400W standard metal halide lamp and a 400W pulse-start metal halide lamp:

Table 2. Comparison of metal halide systems. Source: Acuity Lighting Group.

The pulse-start lamp produces 17% higher initial lumens and 31% higher maintained lumens. Lumen maintenance is 65% of initial light output at 40% of life for a standard 400W metal halide, and 78% of initial light output at the mean for a 400W pulse-start metal halide. But with a modest savings in wattage, how can pulse-start lamps reduce operating costs when substituted for standard metal halide?

Reduce the number of fixtures: Due to pulse-start lamps producing higher light output and much better lumen maintenance, the total fixture count may be reduced. Consider a 100,000-sq.ft. application with a 20 ft. fixture mounting height and a target maintained light level of 50 fc. In this application, we would need 290 standard 400W metal halide fixtures, and 208 pulse-start 400W metal halide fixtures, a 30% reduction in capital and operating costs.

Replace standard metal halide with lower-wattage pulse-start: The second option is to reduce the wattage of the pulse-start system to 320W, which produces light output roughly comparable to a standard 400W metal halide fixture. In our same example installation, 290 standard 400W metal halide fixtures would be required, or 290 pulse-start 320W metal halide fixtures. This results in energy cost savings of roughly 20%.

Dimming: One of the most effective means of reducing HID lighting energy costs is through advanced lighting control strategies such as dimming. Pulse-start electronic dimming HID ballasts are available that not only provide dimming capability (from 100% to 50% system power, 100% to 30% light output, for a 400W metal halide lamp), but can improve lumen maintenance even further. These ballasts can be connected to occupancy sensors, photocells, controllers or switches that dim the lamps based on detected occupancy, ambient light level, a preset schedule or manual input. Some fixtures are available with an integral dimming ballast and occupancy sensor for direct replacement of standard metal halide fixtures or new construction.

(For more information about HID lamp dimming, see the Lighting Controls Association special report, “Dimming HID Lamps,” by clicking here.)

Figure 2. DynaVision® from Advance Transformer is a microprocessor-based electronic metal halide dimming ballast that provides high lumen maintenance and opportunities for operating cost reduction, both through energy savings and lower maintenance requirements. DynaVision also eliminates color shift and lamp blackening while providing automatic lighting control.

In addition, pulse-start lamps can be specified as ceramic arc tube lamps (CDM or CMH lamps). Ceramic metal halide lamps were first introduced in 1994 after Philips engineers essentially borrowed a ceramic arc tube from a sodium lamp and put it in a metal halide lamp to create something entirely new. The final result was a lamp that produces a crisp, white light and provides superior color appearance and color control qualities than standard metal halide lamps. These qualities have made them ideal for color critical areas such as atria, lobbies, retail and similar spaces where color quality is important.

“The footcandles per watt performance of pulse-start or ceramic metal halide with high-performance dome and electronic ballast is very similar to T5HOs or T8s with electronic ballasting and good reflectors,” says Walerczyk. “Because metal halide ballast pricing is significantly coming down, T8, T5HO and electronically ballasted pulse-start metal halide hi-bays may cost nearly the same. Although some of the dimming electronic metal halide ballasts cost significantly more, their flexibility and performance can often provide the best total solution in some applications.”

He adds, “Don’t automatically jump on the T5HO bandwagon, like so many have. The bottom line is that no single technology is superior for all applications.”

Table 3. Ceramic metal halide lamp performance. Source: Philips, OSRAM, GE.

Induction lighting
Some manufacturers have recently introduced induction lighting fixtures as a replacement for HID fixtures in high-ceiling applications. Like fluorescent, induction lighting offers the benefits of instant on and instant re-strike, ability to be used with occupancy sensors, lamp-to-lamp color consistency, good lumen maintenance, and negligible color shift. Primary advantages include compact fixture size, up to 100,000-hour rated lamp life, and retained performance in extremely cold conditions.

An induction system is similar to a fluorescent system in that mercury in a gas fill inside the bulb is excited, emitting UV radiation that in turn is converted into visible white light by the phosphor coating on the bulb. Like fluorescent, the phosphor coating determines the color qualities of the light. Fluorescent lamps use electrodes to strike the arc and initiate the flow of current through the lamp, which excites the gas fill. Each time voltage is supplied by the ballast and the arc is struck, the electrodes degrade a little, eventually causing the lamp to fail. Induction lamps do not use electrodes. Instead of a ballast, the system uses a high-frequency generator with a power coupler. The generator produces a radio frequency magnetic field to excite gas fill. With no electrodes, the lamp lasts longer. Induction lamps, in fact, last up to 100,000 hours, with the lamp producing 70% of its light output at 60,000 hours. In other words, their rated life is 5-13 times longer than metal halide (7,500 to 20,000 hours at 10 hours/start) and about seven times longer than T12HO fluorescent (at 10 hours/start).

Long life with subsequent maintenance and lamp replacement savings, combined with high system efficiency, result in life-cycle cost savings for the owner.

Figure 3. The Ultra Induction Bay (UIB) fixture from 1 st Source Lighting.

Induction lamps are ideally suited for high-ceiling applications where the lamps are difficult, costly or hazardous to access. They are also ideally suited for such applications where the advantages of fluorescent lighting are sought but a light source is needed that can start and operate efficiently in extremely cold temperatures. As a result, induction lighting is a suitable for a wide range of applications, including not only warehouses, industrial buildings, cafeterias, gymnasiums, etc., but also signage, tunnels, bridges, roadways, outdoor area and security fixtures, parking garages, public spaces, and freezer and cold storage lighting.

Induction lighting poses several disadvantages. These lamps cannot be dimmed. Induction lighting cannot retrofit existing HID fixtures without a dedicated retrofit kit. In addition, an induction system can cost up to 4+ times more than an HID system.

Table 4. Characteristics of an example induction lighting system. Source: OSRAM SYLVANIA, Inc. Philips’ induction lamp is the QL, which goes up to 165W in wattage.

Fluorescent fixtures for high/low bay applications
Fluorescent fixtures for high-ceiling applications are compact and offer single-point pendant mounting for retrofit of HID fixtures. These fixtures house 2, 3, 4, 6 or 8 lamps to provide various levels of light output. The lamps may be T8 or T5HO. The optics provides narrow and wide distributions. A few models are available that can operate in demanding environments. Manufacturers include Lithonia, Holophane, Columbia Lighting, Cooper Lighting, Day-Brite, HE Williams, Orion, Simkar, Intrepid, 1 st Source Lighting, Stonco and others.

Figure 4. HB Fluorescent High Bay Fixture from Lithonia. Designed for mounting heights up to 35 ft., ideal for retail, manufacturing and warehouse applications. The fixture provides a choice of optical systems. Narrow distribution best for aisle applications; wide distribution best for lower mounting heights or open general areas. Choice of T5HO or F32T8 lamps in 4- or 6-lamp configuration. Available with or without uplight. Suitable for single- or multiple-point mounting. Click here for a spec sheet (PDF).

Fluorescent lighting offers a number of advantages versus metal halide lighting, including higher efficiency/energy savings, higher lumen maintenance, instant on and re-strike, emergency ballasting options, higher color rendering ability, negligible color shift, lamp-to-lamp color consistency, wide range of color options, and longer lamp life versus 250W metal halide lamps. In addition, fluorescent lamps, as a linear source, offer potentially more uniform lighting, less shadows and less glare. Fluorescent is also easily and inexpensively dimmable and is friendly with switching and control strategies using devices such as occupancy sensors, photocells and scheduling systems.

Figure 5. Fluorescent fixture upgrades in high/low bay applications can increase light levels. The left photo shows a warehouse aisle application lighted standard metal halide, while the right shows an aisle lighted with high-output fluorescent. Courtesy: SpecLight, an Acuity Brands Company.

The most popular choices among fluorescent lamps for applications with high fixture mounting heights are T8 and T5HO lamps.

T8 Lamps: T8 lamps provide long rated life, good color rendition, virtually instant re-strike, and good initial and maintained efficacy and lumen maintenance. For the highest amount of light output for high fixture mounting heights, high-lumen (Super T8) lamps can be specified with the same wattage. To produce the same amount of light as metal halide, however, more fixtures may be required. As a result, T8 may not considered economical for applications with >20 ft. mounting heights, and therefore may be considered unsuitable for a number of high-bay applications. (Walerczyk, however, says that T8 fixtures have been used effectively at very high mounting heights.)

T5HO Lamps: T5HO provide good lumen maintenance and efficacy, long rated life, good color rendition, and virtually instant re-strike. A T5HO system is not as efficacious as T8 lamps, but produces more light output for the same number of lamps. T5HO lamp operation is also optimized at a higher ambient temperature than T8s, good for warmer applications.

Table 5. Comparison of nominal four-foot lamp types. Source: OSRAM SYLVANIA, Inc.

*54W T5HO and 32W T8 light output values are for 3000K, 3500K and 4100K lamps, not 5000K, 6000K or 6500K, which will generally be slightly less.

You may hear fluorescent advocated for quality of light reasons. Says Walerczyk, “For some applications, well-designed linear fluorescent hi-bays are better than well-designed HID hi-bays with regard to glare, contrast ratios and vertical footcandles. Here are two examples. Imagine yourself playing volleyball. As you follow the high arching ball coming towards you, would you prefer having to look up into a point source HID bi-bay or a 4- or 8-ft.-long fluorescent hi-bay with four T5HO or six T8 lamps? Imagine yourself as a forklift driver having to deal with vertical surfaces and load and unload pallets in high warehouse racks. Compare vertical footcandles with well-designed 4-ft., 8-ft. or extended-row linear fluorescent hi-bays mounted in the middle of rack aisle row parallel to the racks with well-designed HID hi-bays mounted in the middle of rack aisle row. Envision how easily a loaded pallet can block the light from the point source HID lamp.”

In other cases, he adds, quality is on the side of metal halide. “For other applications such as retail, pulse-start or ceramic metal halide in clear prismatic hi-bay domes provide more uniform uplight, can be considered more aesthetically pleasing, and maintain the traditional hi-bay look, compared to most fluorescent hi-bays with or without uplight,” he says.

More on T5HO systems
T8 lamps are commonly used in a broad range of applications, while T5HO is a relative newcomer. According to the National Electrical Manufacturers Association (NEMA), T12 lamps now make up about 65% of the lamp market while T8 lamps have 33% and T5 and T5HO lamps now comprise the remaining 2%.

As T5HO lamps are relatively new and used less than T8, let’s take a moment to examine this lamp type more closely.

The T5 high output lamp, or T5HO, was introduced to North America in 1998. T5HO lamps produce twice the light output of a T5 lamp while being the same length, and about twice the light output of a T8 or T12 lamp. The nominal light output of a 4-ft. 54W T5HO lamp is 5,000 lumens, compared to 2,900 lumens for a 28W T5 lamp and 2,850 lumens for a 32W T8 (Super T8 lamps are rated at 3100+ lumens).

Below are key points to consider about T5HO lamps:

Diameter: Being 5/8-in. in diameter, T5HO lamps are about 40% of the size of T12 lamps. The thinner lamps enable better photo-optic control of the light produced by the fixture, increasing efficiency and providing uniform distribution of its light output.

Metric dimensions: T5HO lamps are built to metric dimensions. The 4-ft. T5HO lamp, for example, is 45.8 inches long, a little shorter than T8 and T12 lamps. The lamps are therefore not interchangeable.

Ambient temperature: Note that initial rated light output for T5 and T5HO lamps is based on peak output at an ambient temperature of 35 ºC (95 ºF), whereas T8, T12 and circular T5 lamps are based on 25 ºC (77 ºF). This characteristic of T5HO lamps may make them more suitable than T8 in some industrial applications in which ambient temperatures may be higher.

Wattages & lengths: T5HO lamps are available in 24W, 39W, 54W and 80W in nominal linear lengths of two, three, four and five feet respectively, and in a 55W circular shape. The four-foot 54W lamp is most common.

Ballast: T5HO lamps are designed to operate on programmed start or instant start electronic ballasts. The programmed start ballast maximizes lamp life, particularly in frequently switched applications, whereas the instant start ballast may reduce wattage. Universal-voltage (120-277V and 347-480V) ballasts, dimming ballasts, and four-lamp ballasts are available. T5HO ballasts operate on a different current than other ballasts, and therefore aren’t compatible with T8, T12 and T5 lamps.

T8 vs. T5HO
You may hear recommendations to use T8 fixtures for a better quality of light and less glare at fixture heights <20 ft., T5HO fixtures for quality light output and higher fixture efficiency at fixture heights >20 ft., and either between 18 and 25 ft. However, while T5HO may produce “glare bombs” at lower mounting heights, both T8 and T5HO fixtures can be used in low-bay and high-bay applications. Says Walerczyk, “I have seen time and time again that T8 lamps can work just as well in applications with very high fixture mounting heights.”

Figure 6. In this school gymnasium, 400W metal halide fixtures (LEFT) were changed over to F32T8 industrial fixtures (RIGHT) at a one-for-one replacement, increasing light levels from 30 to 50 fc and CRI from 65 to 85 while reducing wattage per fixture from 450W to 224W. Courtesy: SpecLight, an Acuity Brands Company.

When choosing T8 versus T5HO, light level will be a prime consideration, but several other factors should also be considered.

Ease of replacement is a factor that should be considered. To get higher light output from a T8 fixture, Super T8 lamps (3,100+ lumens) should be specified, but the owner must continue to order this lamp type to maintain lighting performance without substituting to lower-output (and less expensive) T8 lamps that may be used elsewhere in the facility, such as in offices. If standard T8 lamps are substituted for Super T8 lamps, the application will experience lower light levels than expected. Typically, Super T8 and T5HO lamps are only available from lighting and electrical distributors.

Another factor is the presence of advanced controls to optimize the performance of the lighting system, increase flexibility and maximize energy savings. If occupancy sensors are used and the lamps are frequently switched, lamp degradation will occur after 12,000 to 15,000 switching cycles on a T8 lamp operated on an instant start electronic ballast, the most common T8 ballast type. Some lamp manufacturers may not warranty their T8 lamps when operated on instant start ballasts and controlled by occupancy sensors, and at least one will provide a warranty if the delay setting is at least 20 minutes.

T5HO electronic ballasts are programmed start ballasts, which provide 100,000 cycles without lamp degradation, significantly prolonging lamp life in frequently switched applications. To get the full rated life from a T5HO lamp, ANSI, IEC and the major lamp manufacturers state that it must be operated with a programmed start ballast.

However, there are several F32T8 models that are rated for 24,000 hours with instant start ballasts at 3-hour cycles. At 1.5- to 2-hour cycles, the lamps may last almost as long as 3-hour cycles, which is the industry standard.

Several ballast manufacturers are planning to offer high ballast factor program start T8 ballasts in 2005. The current industry standard high ballast factor is 1.18; four Super T8 lamps operating on a high ballast factor ballast, therefore, would produce 14,632 lumens, compared to 20,000 for four T5HO lamps (with a ballast factor of 1.0).

Programmed start ballasts are more expensive and are series-wired, meaning that when one lamp burns out, the remaining lamps will light only dimly or fail to light. (However, four-lamp ballast designs are available that are “series-parallel.” The ballast isolates one two-lamp “leg” from the other two-lamp leg, with each leg operated in series, and then operates both legs in parallel. This ensures that if one lamp expires in one two-lamp leg, the other two-lamp leg will continue to operate normally.) Instant start ballasts are parallel-wired, which means that when one lamp fails, the other lamps on the ballast will continue to light normally.

T5HO fixtures are also designed to operate optimally at higher ambient fixture temperatures (35ºC or 95ºF), which may make this lamp a more desirable choice in applications with warmer ambient temperatures at the fixture mounting height. Conversely, T8 fixtures may be more desirable so as to get better performance from a fluorescent lighting system in cooler applications, particularly when used with occupancy sensors, so as to achieve full light output quickly.

Walerczyk warns that ambient temperature surrounding the fixture is not in itself critical, but ambient air temperature in the lamp compartment of the fixture is; some T8 and T5HO fixtures have good temperature design, while some do not, he says.

In addition, specifiers and owners should be aware that it is generally desirable to select fixtures with optics that are specially designed for T8 or T5HO lamps, rather than T12 fixtures that are converted to operate with T8 and T5HO. Buyers should always beware that they will get what they pay for. Some imported T5HO fixtures may be cheap, but they may not perform sufficiently for the application, sacrificing quality.

Figure 7. T5HO lamps produce maximum light output at 35ºC or 95ºF ambient fixture temperature, while T8 lamps produce maximum light output at 25ºC or 77ºF. Courtesy: SpecLight, an Acuity Brands Company.

Fluorescent vs. metal halide
At first glance, it may be difficult to understand how a 400W metal halide lamp, which is rated to produce 36,000 initial lumens, can be replaced one for one by four T5HO lamps. The answer is in lamp lumen depreciation—the rate at which light output declines over time. Standard metal halide lamps experience a higher level of lamp lumen depreciation than T5HO and T8 lamps. A 400W metal halide lamp can lose 35% of its light output at 40% of life, while a T5HO fluorescent will lose only 5-6% of its light output.

Figure 8. Lumen maintenance curves for metal halide and T5HO. The “M400” lamp is a 400W metal halide, and the “MS400” is a pulse-start metal halide. Courtesy: SpecLight, an Acuity Brands Company.

Looking at mean lumens, a 6-lamp T5HO system produces about 20% more light output while consuming about 20% less energy than a 400W metal halide.

(Another option is a 4-lamp F96T8/HO, which also produces 20% more light output while consuming 20% less energy; Walerczyk, however, sees 8-ft. T8HO lamps as expensive, and believes an 8-lamp F32T8 fixture with 1.15 ballast factor ballasting is a better option.)

Table 6. Comparison of 400W probe-start MH system with competitive pulse-start MH, T5HO and T8 systems. Two values are shown for pulse-start MH systems to show a lamp operated on a magnetic vs. electronic ballast. Source: Advance Transformer Company.

In addition, the fluorescent system will provide instant on and re-strike, softer light distribution (less shadows), greater friendliness with automatic control strategies, negligible color shift, greater color rendering, relatively easy and inexpensive dimming, emergency ballasting options, wide range of color options, and lamp-to-lamp color consistency.

New line-voltage occupancy sensors have significantly reduced the installed cost of occupancy sensors, making it economical to install one sensor per fixture for spaces that are intermittently occupied and maximizing energy savings. Fluorescent fixtures also add flexibility in that the lamps can be wired for energy-saving switching strategies or emergency lighting ballasting. They can also be dimmed, using a dimming ballast, the full range of light output to save energy, provide the ultimate in flexibility for multi-purpose spaces, and provide security lighting after hours.

Despite the advantages of the fluorescent option, however, it will result in 4-6 times the number of lamps to maintain, which can present a significant ongoing maintenance cost (labor, the lamps will be less expensive). Fluorescent manufacturers, however, argue that when a fluorescent lamp fails, the other lamps continue to produce some light, whereas when a single metal halide lamp fails, a significant amount of space will not have a sufficient light level.

In addition, while one-to-one fluorescent to metal halide fixture replacement is often feasible, potentially up to 2-3 times the number of fixtures may be required to purchase and install. In addition, if the building is unheated, the lamps will experience performance problems in extremely cold temperatures related to starting, efficiency and light output.

Table 7. High-performance metal halide, T5HO and T8 hi-bay comparison. Source: Stan Walerczyk , LC. Click here to see the table, which will open in a new window.

More on Controls
“With today’s technology, fluorescent and HID can be operated in the same manner. In HID systems, hi-lo type of systems have been around for many years and in most cases work very effectively,” says Howard Yaphe, Senior VP Manufacturing and Engineering for Canlyte. “Fluorescent provides an opportunity for finer control resolution. In long aisles, why should the total aisle illuminate to a high level if the operator is only picking through the first bin? Addressable technologies such as DALI will permit finer resolution for greater energy savings.”

Yaphe adds, “In all cases, it is occupancy sensing that provides the greatest savings opportunity. With HID, you have no choice but to use hi-lo type systems because of the re-strike constraints. In fluorescent, you could have dimming strategies but you could also have hi-lo systems as well where some ballasts are on all the time and others operate with the occupancy sensor. In open areas, daylight strategies are possible, coupled with occupancy-sensing.” In addition to occupancy sensing and daylight harvesting, Yaphe points out that lumen maintenance dimming is also viable, particularly with HID lighting, and task tuning, which, he says, usually requires an addressable system.

In Stan Walerczyk’s view, daylighting deserves more attention as a great opportunity for energy savings with controls. “Warehouses, big box retail, industrial facilities and gyms are great applications for skylights, which can save kWh and, more importantly, peak load,” he says. “I hate to see hi-bays fully on during the middle of the day that are underneath or right next to skylights. What a waste!”

He adds, “Performance is better with a magnetic high/low HID hi-bay and dual-stage photoswitch. Dimming electronic-ballasted HID and a continuous photocontrol is even better.”

Regarding fluorescent control, Walerczyk says, “Daylight harvesting is very easy with fluorescents, because they have instant on and no re-strike time. Fluorescent hi-bays can be staged dimmed (step-controlled) with multiple fixed output ballasts and continuously dimmed with dimming ballasts.” Continuous dimming, however, is easier for the eye to adapt to. “In addition to windows and skylights, another good application is installing a photocell to fluorescent hi-bays close to large roll-up doors to turn off power when there is sufficient daylighting.”

The final word: “It is critical to budget sufficient time and money to properly commission occupancy sensors, photocontrols and other controls.”

Projects
Below are several organizations that benefited from upgrading its metal halide lighting systems:

Timken Aerospace: Timken Aerospace chose fluorescent when it upgraded its 142,000-sq.ft. manufacturing plant in Lebanon, NH. Because the facility makes precision ball bearings, high-quality lighting is required. The lighting operates around the clock, every day. In 1999, Timken upgrade 543 standard 400W metal halide low-bay fixtures with 2x4 232W T5HO fixtures from MetalOptics. The project, implemented by Timken personnel, cost $268,000 and benefited from a rebate of $91,500 from Granite State Electric, the plant’s utility. Timken reduced its demand by 120kW and saved more than 1,000,000 kWh, an annual savings of $70,200, resulting in a payback of 2.5 years. Timken also achieved its goal of high-quality lighting.

World Gym Racquet Ball Courts: World Gym retrofitted eighteen 400W metal halide fixtures each with four T5HO Biax lamps, reducing demand by 3.96kW and energy consumption by 54,810kW, or about 50%, resulting in $3,735 in savings per year. The investment yielded a simple payback of 1.8 years. Significant energy savings resulted from the installation of advanced lighting controls, which reduced the hours of operation by 55%. The new T5HO system provided 34% more light than the metal halide in addition to improved color quality.

Figure 9. World Gym Racquet Ball Courts project. On the right, we see an existing metal halide fixture. On the left, we see a fixture after the retrofit to T5HO biax lamps. Courtesy: Sacramento Municipal Utility District (SMUD).

Galt High School gymnasium and auditorium: Galt High School upgraded 57 standard 400W metal halide fixtures with 57 four-lamp T5HO fixtures, reducing demand by 12.3kW and energy consumption by 41,057kWh, or nearly 50%, resulting in energy cost savings of $2,863 per year. Light levels were improved from 25 fc to 39 fc. The athletic coach said, “I’m very impressed; the lighting is even, no dull areas. This is the type of lighting that should have been originally installed.”

Figure 10. Galt High School upgraded its metal halide fixtures with T5HO linear fixtures, reducing energy consumption by nearly 50%. Courtesy: Sacramento Municipal Utility District.

The last word
Fluorescent lighting offers many advantages versus metal halide lighting in high/low bay applications, but can present several trade-offs. Potentially viable alternatives include induction and pulse-start metal halide with dimming capability.

As always in lighting, the choice of the best system will often depend not just on the economics of initial and operating cost, but also on environmental considerations and what level of performance the owner is looking for from their lighting system.

“If any company tries to convince you that HID, T8, T5HO, CFL or induction is the best single general solution [for all applications], find another company,” advises Walerczyk.

“Make your own comparisons,” he further recommends. “Include quality of light, end-of-life horizontal and vertical footcandles, dirt depreciation, glare, distribution, shadowing, spacing criteria, system wattage, initial parts and installation costs, ambient temperature range, ballast case temperature ratings, warm-up and re-strike times, control flexibility, replacement lamp cost, labor cost for maintenance, and lift rental costs. Also compare options within options, like apples-to-applies comparisons of various T8 hi-bays.” He adds, “Whatever you do, do not choose standard metal halide, standard high pressure sodium, or basic-grade dome fixtures.”

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