The need for multiple air filters in cleanroom facilities leaves minimal space for light fixtures. There are three common fixture styles for cleanrooms that maximize the use of the space: recessed troffers, surface-mount fixtures, and surface-mount teardrop fixtures. These are best-suited for use in cleanroom facilities, depending on ISO classification.
Recessed troffers: These fixtures are ideal for cleanrooms designated with an ISO 8 to ISO 5 classification because they have enough space in the ceiling and plenum. While rooms with an ISO 8 and ISO 7 classification have more space in the plenum than rooms with a classification of ISO 6 or ISO 5, both environments can use recessed fixtures. Environments with these classifications are typically electronic assembly, pharmaceutical processing, semiconductor manufacturing, and chemical lab facilities.
Surface mounts: For more demanding environments—those with ISO 3 and ISO 4 classifications—surface-mount fixtures can be installed below the ceiling plane. Because of the high air-filtration level required, there typically is not enough plenum space for recessed troffers so surface-mount fixtures are especially efficient.
Surface-mount teardrops: Surface-mount teardrop fixtures are suitable for controlled environments with an open-area design and moderately demanding classifications of ISO 5 and ISO 4. These fixtures are mounted to a 2-in.-wide ceiling grid and are suitable for individual or continuous row mounting. The aerodynamic shape of the teardrop fixture minimizes any disturbance of the laminar airflow.
This cleanroom tip was taken from "Key Considerations When Specifying Cleanroom Lighting" by Jamie Pearson, Acuity Brands Lighting.