It's no mystery that cleanrooms present numerous challenges to designers who specify lighting systems. Cleanroom lighting will vary depending on the room's use, its classification and ceiling air supply configuration. In an ideal situation, lighting systems should provide good visibility and be designed with contamination control issues—electromagnetic field generation and cleanability—in mind. But before that can be achieved, a thorough examination of the basic fundamentals, illumination requirements, available styles and fixture construction must be undertaken.
Fundamentals
Considering the fundamentals, the purpose of lighting systems is to provide visibility. Issues such as initial costs, energy, and maintenance costs typically contribute to lighting design decisions in most facilities, but for a cleanroom facility, the cost of lighting fixtures typically represents less than 1 percent of the total budget. Energy costs associated with lighting are usually minimal compared to the cleanroom HVAC and process equipment power demands. The focus in cleanroom lighting then becomes proper illumination, coordination with air supply systems and reduction of contamination for the unique environments and processes that reside in the space.
The unit of lighting luminance in the United States is the foot-candle, which equals 1 lumen per square foot. Lumens are used to describe the light output (luminous flux) of the source. The foot-candle level required in cleanrooms has been historically high due to precision demands or the extremely small size of the object that requires attention. Illumination levels vary depending on the different process areas within the cleanroom. The engineer or lighting designer is encouraged to review each process area within the cleanroom to determine the type of task to be performed and the illumination levels desired.
The surfaces of most cleanrooms tend to be highly reflective. Most or all of the ceiling, walls and flooring are bright white with enamel-like surfaces. However, wall and flooring material color options are being reexamined to improve the user environment.
The air supply system further complicates lighting placement and spacing. In more restrictive cleanroom classes, most or all of the ceiling consists of air supply filter panels with no space left over for recessed lighting fixtures; however, a thoughtful design process must assure optimum visual comfort and efficiency to support the performance of tasks in the cleanroom. As we'll see, there are various lighting solutions—most utilizing fluorescent lamps.
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