Lighting Design + Application • October 2003 - Illuminating ...

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DESIGN TRENDSAlthough “teardrop” fixtures are sometimes used because oflimited ceiling space, they have a number of serious–andsometimes critical—drawbacks.be extremely tight and that an effective technique forinterfacing the housing with the ceiling is essential.The integrity of these leak-prevention characteristics hasto last long after installation, since clean rooms must notonly be certified upon completion, but recertified eachtime a containment wall or ceiling is compromised—something that can occur during the performance of routinemaintenance or repairs. These maintenance andrepair procedures are so interruptive to the function of thespace, that many organizations close down clean roomoperations up to several weeks each year to perform them,also providing a window for such routine operations asrelamping fixtures.• Multiple Visual Tasks. Historically, research laboratorieswere either “wet” or “dry” in their function, with wetsciences such as biology and chemistry residing in onespace and dry disciplines such as computer science andstatistics in another.A new generation of laboratories, however, combinesboth wet and dry disciplines within the same researchgroups, resulting in compound lighting requirements.Clean Room GuidelinesSuccessfully addressing these issues from a lighting layoutand luminaire specification perspective calls for a lightingprofessional’s traditional skills combined with specializedclean room knowledge. And, while a comprehensivediscussion of all necessary clean room information isn’tpossible in a single article, there are some key points thatcan be extremely helpful to those involved (or who plan onbecoming involved) in clean room lighting.• Bring Lighting Into the Picture Early in theDesign Process. Dealing successfully with the problemof too little ceiling real estate for proper lighting calls forcoordination between the architect, mechanical engineerand lighting specifier early in the design process.Typically, the need for the appropriate level of cleanlinesscertification puts the mechanical engineer in the driver’sseat, since the M.E. is responsible for such things as meetingair filtration requirements and providing the necessarymechanical and life safety systems. When mechanicalsystem designs are completed before lighting is considered,an effectively lit environment is nearly impossibleto achieve. And, while working together on lightingneeds up-front can’t change the M.E.’s primary responsibilities,it can provide the opportunity for a coordinateddesign effort that allows the M.E. to make whateveraccommodations are possible.• Choose Fixtures with Materials Appropriate toSpecific Cleaning Protocols. Knowing how fixtures willbe cleaned and maintained informs the specifier about thematerials requirement while also potentially increasinglighting calculation accuracy. The first part is obvious, sinceLensed, flush-mounted 2x4 troffers are the preferred fixture-typefor most clean room applications, but they must be speciallydesigned, constructed and tested to ensure they won’tcompromise the facility’s ongoing cleanliness requirements.. . . . . . . . . . . . . . . . . . . November . . . . . 2003 . . . LD+A . . . . 64. . www.iesna.org. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DESIGN TRENDSunderstanding the protocol allows specification of luminairesconstructed from materials that will stand up to thecleaning process. (Cleaning solutions are typically a combinationof alcohol and industrial detergents.) Becausemost fixtures weren’t designed for clean room use, it’s criticalto specify only materials that have been independentlyverified to withstand the specific cleaning protocol.Housings and other metal components should be stainlesssteel, lenses should be laminated glass (tempered glass isrequired for hazardous applications), while gaskets shouldbe silicon-based.Less obvious is how maintenance protocols can influencethe values chosen for illuminance calculations.Protocols that include frequent area maintenance shutdownscan indicate that group relamping will occur morefrequently than the manufacturer recommends, so lumenoutput may be greater during the lamps’ use than in moretypical scenarios. Combined with an extremely low dirtdepreciation factor, the resulting light levels will be higherthan in other applications.• Select the Right Fixture Type for the Application.In most cases, specially designed, 2X4 recessedlensed troffers are the preferred fixture type, offering achoice of lamping and lensing options and doing a betterjob of limiting surface brightness and distributinglight than either 1X4 lay-ins that do an inferior job oflighting distribution (as well as increasing cost due to therequired use of additional fixtures, or) surface-mounted,two-inch wide “teardrop” fixtures that are overly brightand, like the 1x4, aren’t as good as 2x4s in providing anevenly-lit environment.While teardrop fixtures may be used in some positivepressureapplications, they’re not readily accepted due tothe fact that they don’t stand-up well to wet swabbing andare constructed of aluminum and plastic components. Onthe other hand, they can actually pose danger in negativepressure, bio-containment applications. Being inherentlydifficult to seal, organisms can potentially penetrate thefixture, finding a warm, welcoming environment in whichto multiply and grow resistant to the cleaning protocol.In these bio-containment facilities, appropriately-engineeredand constructed recessed fixtures with lenses flushwith the ceiling typically provide the fewest opportunitiesfor organisms to invade the luminaire and grow independently,meaning that the reservation of adequate space forrecessed troffers should be a high priority.Another means of determining a fixture’s appropriatenessfor an application is its cleanliness rating. For applicationswhere fewer than 100 pieces of particulate percubic foot of space are allowable, for example, the fixturemust be listed as a Class 100 certified fixture. Typical cleanroom classifications include Class 100,000, Class 10,000and, for the most demanding environments, Class 100. Aswill be discussed later, however, cleanliness classifications
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Page 12 and 13: GREEN IDEASTaking the LEED in Light
Page 14 and 15: ENERGY ADVISORWillard L.Warren,PE,
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Lighting Design + Application • October 2003 - Illuminating ...

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