To make the most efficient lighting selection, know your requirements and your options
By Robert Catone, Guth Lighting
Although the lighting field has seen many technological improvements over the last decade, many challenges remain for design teams working to specify the best technology systems for environmentally controlled environments. The biggest challenge is that there are no formal standards for cleanroom lighting, largely leaving the selection process up to whatever the specifier deems to be important and sufficient.
There are, however, a great number of clean-space standards that have a direct impact on proper lighting selection and installation, the most widely recognized being ISO 14644-1, which establishes the acceptable levels of particulates for various classes of cleanrooms. And, there are a great number of regulatory and inspection agencies-such as the FDA for the pharmaceutical and biopharmaceutical industries-that monitor and evaluate the cleanliness levels of lighting fixtures.
In the food industry, there are nine broad categories of processes (poultry, dairy, bakery, confectionary, meat, beverage, fish, vegetables and prepared foods), and there are numerous regulatory agencies (FDA, OSHA, USDA) that inspect for sanitation and safety. At the lighting equipment manufacturing level, the National Sanitation Foundation (NSF) International certifies fixtures for use in food-contact and splash-zone areas.
As a result, cleanroom and clean environment contractors and users need to have a thorough understanding of the different types of lighting, lighting fixture and installation options available.
Lamps
The best place to start is with an evaluation of the different types of lighting available for clean spaces. The most common lamps for areas below 10 feet are linear and compact fluorescent, with metal halide lamps reserved for higher mountings.
Among the most important factors to consider is lamp lifetime, taking into account not only the initial cost of the lamp but the cost to replace it. For example, in some cleanrooms, the relamping of a fixture may require recertification of the entire cleanroom because the fixtures have been opened up. This is why the new 40K-hour lamps are of particular interest in the cleanroom industry, providing eight years of lighting without having to change a bulb, and most users are happy to pay an additional $2 to $3 for the lamp.
Lamp lifetime is largely a function of the type of phosphor used. Lower grade phosphors, such as those used in F32T8-741 type lamps, equate to a cost of about $1.25/lamp but have a much shorter lifetime than the F32T8-XXL, which costs about $3.50/lamp but has a 40K-hour lifetime (see Table 1).
Color accuracy is also dependent on the type of phosphor used, with some of the newer phosphors providing much better color accuracy. In the table of linear fluorescent lamps, 82.5 is the lowest performance with the highest being 91.4. This relates to the relative color accuracy compared to incandescent lamps, which are rated at 100. Some specialized lamps can achieve accuracies as high as 95 percent, which is an important factor for some applications such as food processing where vegetable color in an inspection line is critical. Superior color accuracy can also be an important aesthetic factor for some architects. For most applications, however, color accuracy above 80 is adequate given the average ability of most individuals to discern differences.
Lamp types
There are several different lamp types available with varying performance characteristics to suit a range of applications.
 Table 1: Performance characteristics of linear fluorescent lamps |
Linear fluorescent
These four-foot-length tubular lamps are available in varying levels of quality and performance, with the one-inch diameter T8 having replaced the T-12 as the standard. The metric 46” T5HO lamp is also being used with some exotic fixtures. These lamps operate best between 0°F and 85°F. Table 1 shows the performance characteristics of different linear fluorescent lamps.
 Table 2: Performance characteristics of compact fluorescent lamps |
Compact fluorescent
These 4- to 11-inch lamps have become popular in down-lights and small architectural fixtures. In some cases, multiple lamps allow stepped light levels and energy management. They are replacing low-wattage metal halide in many applications. The starting temperature can be as low as -22°F. Lumen output is stable up to 140°F (see Table 2).
 Table 3: Metal halide performance with electronic ballasts |
Metal halide
Metal halide lamps provide white light and are unaffected by temperature. Their starting temperature can be as low as -20°F. Lamp re-strike can take 2 to 6 minutes after a power outage. These lamps are used from 10 to 40 feet (see Table 3).
Specialty lamps, coatings and sleeves
In addition to the more commonly used lamp types described above, there are also a number of specialty lamps available offering unique features and capabilities. For example, induction lamps are an expensive fluorescent system operated by microwave energy. These lamps provide 100,000 hours of life and are available from 60 to 165 watts. They are particularly useful in cases where maintenance is expensive.
Another example is special color spectrum lamps, which have tinted sleeves or lenses to control UV or provide special colors for animal environments or custom applications. Break-proof lamps are available from coating companies and some manufacturers. Teflon is generally used to contain the broken glass.
Another option, light emitting diodes (LEDs) can provide 50,000 hours of life when properly heat sunk. These systems are expensive, however, and white-light efficiency is about 35 percent that of fluorescent lamps. It is the primary lamp for signage and exit lights.
Electronic ballasts
Electronic ballasts are the standard for fluorescent lamps and are also quickly becoming the standard for metal halide lamps as well (see Fig. 1). New, high, 1.3-ballast-factor designs increase T8 fluorescent lumens per lamp up to 35 percent. Since ballast life is shortened when case temperatures are at their limits, manufacturers also offer premium higher-temperature versions. Daylight harvesting, load shedding and automatic dimming features have all been integrated into the newer ballast designs, providing the following standard and optional benefits: efficient lamp performance, quiet operation, integral dimming or step dimming, end of life lamp shut-off, computer software control, self protection against overheating, universal voltage and lamp operation, small size and minimal weight, and higher T8 lumen per lamp electronics.
Fixtures
The next important factor to consider in cleanroom or clean-environment lighting selection is the type of fixture to be used. Again, cost can be a determinant. In general, stainless steel is the most expensive fixture material available, with aluminum falling somewhere in the middle range and painted steel being the cheapest. Aluminum housings provide the coolest electronic ballast and lamp operation, while stainless-steel housings operate hottest.
 Figure 1. These electronic ballasts provide state-of-the-art operation for fluorescent and metal halide lamps. Photo courtesy of Advance Transformer |
Maintenance, lifetime and replacement costs should also be taken into account in addition to initial fixture prices. For example, many food and pharmaceutical plants will initially opt for cheaper, painted-steel fixtures only to find that after repeated wash-downs, the paint begins to flake or peel and the steel to rust, requiring replacement. It’s often just a question of whose budget will absorb these costs, and the individual responsible for the initial construction budget may opt for the cheaper steel fixtures without consideration to the person responsible for maintenance, whose budget will ultimately be affected.
Cleanroom class level is, of course, a critical consideration. For a Class 10,000 (ISO 7) cleanroom, fixtures are basically a standard unit with a gasket on the door. Additionally, some kind of gasket is used between the fixture and the ceiling grid system supporting it, but the fixture usually has minimal additional protection and in many cases may not be caulked.
For a Class 1,000 (ISO 6) cleanroom, however, all of the ceiling fixtures should be caulked and the fixture doors sealed as well. Some users may require that the lens also be sealed to the door frame. Still, the stringency of the installation will be largely dependent on the person writing the specification, with one person writing a spec for a Class 1,000 cleanroom that is much more stringent than someone else might write for the same class room.
The installer, as well as the fixture supplier, is also an important consideration, especially for sheetrock ceilings vs. grid systems. For example, the installer must cut openings into the sheetrock to house the fixtures. Typically, four brackets are used to hold the fixture in place, with the brackets basically torqued down against the sheetrock and the fixture sitting snugly against it. In some cases, however, the sheetrock ceiling is not perfectly flat (referred to as sag), leaving a gap between the flange of the fixture and the sheetrock. This will be a particular concern if using steel fixtures, which may weigh up to 60 lbs and will not help in maintaining the flatness of the sheetrock.
Aluminum fixtures, weighing about 16 lbs, are more forgiving but the installation contractor should still often be required to caulk the edges of the fixture. Again, it ultimately depends on the level of cleanliness that the user is interested in maintaining.
Fixture types
Recessed troffers, which come in myriad sizes, lamps, gaskets and construction types, are the primary fixture choice for many cleanroom, lab, pharmaceutical and food processing applications. Welded housings should be used with positive plenum pressure rooms. Lenses are generally installed with the smooth side out to reduce dirt accumulation, and louvers with a sealed underlay are available to lower glare in sensitive areas. HID metal halide lamps are usually available in 2’ x 2’ housings for high, insulated ceiling applications.
Surface fixtures are used when ceiling penetration is not desired, and these are available in many sizes, lamps, shapes, materials and gasketing levels to meet the most exacting requirements.
- Teardrop fixtures maximize linear airflow in Class 100 (ISO 5) cleanrooms. Smaller designs for T8 lamps enhance airflow. Lengths are available up to 16 feet.
- Tubes that are sealed and NSF-certified are most popular in food plants but have also found success in vivariums and Class 3 and 4 labs. A variety of lengths, stainless-steel endcaps and moveable mounting straps provide durability, amiable optics and versatility. Optical options provide task, inspection or general lighting.
- Wraparound fixture construction can be plastic, fiberglass, aluminum and caulked or seam-welded stainless steel. Gasketing can provide dust-tight and waterproof listings. Most of these fixtures find use in food processing areas where captive latches are a requirement.
- Lowbay fixtures with metal halide lamps are generally used above 15 feet in food facilities. Designs with smooth contours and rounded surfaces are most popular because they resist dirt build-up and clean easily.
 Figure 2. Lowbays with sealed construction and prismatic lens can create an attractive aesthetic feature in a clean environment. Photo courtesy of Guth Lighting. |
Architectural fixtures are generally used in laboratories with open ceilings. Here, enclosed construction and ease of cleaning should be a priority.
- Lowbay fixtures use 1 to 8 compact fluorescent lamps. Customization provides accent colors that can add variety to the space. Fixtures are 12, 16 or 22 inches in diameter and may have sealed or open optics (see Fig. 2).
- Attractive wraparound and surface fixtures are available with enclosed or gasketed construction. A variety of sizes, lengths and finishes can meet most aesthetic requirements.
Cost factors
For new construction projects, lighting selection is usually not highly price sensitive because it will be relatively insignificant compared to the total cost of the building. Where it does become price sensitive, however, is on retrofits where contractors often try to use the lowest-cost option in order to increase their margins. Sometimes, the user may also wish to keep upfront costs to the bare minimum.
Advances in technology, when properly applied, provide many new ways to save energy and lower construction and maintenance costs in the cleanroom. In future, improved control systems and more efficient lamps will also continue to offer lower energy consumption and operating costs.
Robert Catone is a certified lighting professional, the general manager of Guth Lighting and VP of the JJI Lighting Group. He is a member of the Illuminating Engineering Society’s Progress Committee and credited with 2 lighting patents. Guth (www.guth.com), a division of Genlyte Corporation, was founded in 1902 and specializes in fixtures for cleanrooms, laboratories, pharmaceutical manufacturing and food processing.