Lighting is usually the last thing thought about in a data center design, but inadequate illumination can certainly...
contribute to human error. The ability to clearly see patch panel labels and wire colors is crucial, particularly when working under pressure. And the fact that most cabinets and equipment are flat black today makes lighting difficult in the first place, since little light is reflected within the aisles. But often times fixtures are located above cabinets and cable trays, with little of the light even getting into the aisles. This tip explains principles that IT pros can use to improve cabinet and aisle lighting, while incorporating it with other best practices for data center design.
Data center ceilings are usually built with “lay-in” tile panels in suspended metal grids–similar to those used in most offices. Suspended ceilings have become more common in data centers as the way to create hot air return plenums–a best practice approach for high-density cooling. The panels in data centers, however, should be non-flaking to keep dust out of the air stream.
Architects tend to specify standard fixtures for lay-in grids, because they are easy to install and they match the rest of the building. This brings the advantages of mass purchase pricing and common lamp replacements, which both contractors and facilities like. However, unless the ceiling grid is designed to coordinate with the cabinet rows and other overhead systems, light fixtures can end up fully or partially blocked by cabinets and cable trays, or simply way off-center of the aisle they’re supposed to illuminate.
Ceiling systems are nearly always on a two-foot grid, and it can be difficult to get the light fixtures to line up with aisles unless the cabinets are spaced at the same increment. With a raised access floor that’s not as hard to accomplish, although the floor and ceiling grids are often not specified to line up, and abnormal spacing of just one cabinet row can throw off the whole coordination. Furthermore, lay-in light fixtures are generally large (2-by-4 feet or 2-by-2 feet), so they span a significant amount of an aisle. This can make it difficult to avoid at least partial conflicts with other overhead elements that can block some of the light or create shadows. In all fairness, the architect sometimes never sees a cabinet layout drawing when creating a data center design, so lights are just populated in a standard pattern as if it were an office environment. That can be avoided if IT professionals provide good information early enough in the data center design, or if a knowledgeable consultant is involved. Lay-in fixtures can certainly work if the ceiling grid and cabinet rows are well coordinated, but better choices exist.
The best data center lighting treats the cabinet rows as if they are library book stacks, and architects seem to relate to that analogy. In a library, the goal is to read the titles and catalog numbers on the spines of books. Something around 50-foot candles (approximately 500 lux) on the book surfaces is sufficient. A data center is similar, except we also want light to penetrate as far inside a cabinet as possible when a door is open. This requires a fixture with a wide dispersion pattern, mounted not too far above the cabinets (usually no more than 24 inches). It also requires a fixture size and location that is not blocked by cable trays and other overhead devices. The best choice has heretofore been narrow, carefully selected one- or two-tube pendant fixtures hung in continuous rows. The problem has always been suspending them along with all the other things we now want to put overhead. Coordinating mountings and suspension rods with the ceiling grid can be tricky, and the ceiling tiles can end up looking like Swiss cheese.
A good solution is a ceiling grid that incorporates T-channels for quarter-inch threaded rods. Both lights and other overhead items, such as cable tray and power busway, can be suspended from the grid, located exactly where they are wanted and fully coordinated with each other. Using the ceiling grid track doesn’t require punching holes in the tiles or drilling into the slab above. A fair amount of weight can accumulate, but track-style grids exist with higher structural strengths than the standard ASTM International “Heavy Duty” rating. However, they may need extra suspension wires to support heavier devices.
Lighting is also a place where we can practice energy conservation. Two methods are worth considering. One is to use LED lighting. Bright, energy efficient and low heat, LED fixtures are becoming the lighting of choice in “green” data center designs. Unfortunately, the choice of fixtures is still relatively small, making LED lighting more difficult to use in data centers with high ceilings, but that is bound to change. With a little innovation, available fixtures can be adapted to most situations. There are even LED replacement tubes for fluorescent fixtures, as well as overhead cooling systems with integrated LED lighting.
Any lighting system can also be fitted with proximity detectors to turn the lights on when someone enters an equipment area, and off again when no motion occurs for a predetermined interval. That saves energy as well.
In short, lighting is just as important a part of a data center design as any other segment of the infrastructure. There’s no reason for it to be inadequate or treated as an afterthought in the design. It should be coordinated with the cabinets and other overhead elements so that working areas are well illuminated. It should also be designed with energy efficiency in mind.
About the author: Robert McFarlane is a principal in charge of data center design for the international consulting firm Shen Milsom &Wilke LLC. McFarlane has spent more than 35 years in communications consulting, has experience in every segment of the data center industry and was a pioneer in developing the field of building cable design. McFarlane also teaches the data center facilities course in the Marist College Institute for Data Center Professional program, is a data center power and cooling expert, is widely published, speaks at many industry seminars and is a corresponding member of ASHRAE TC9.9 which publishes a wide range of industry guidelines.