The data center industry is experiencing an increase in the number of businesses deploying equipment cabinets in colors other than the traditional black, with white being the most common choice. Typical reasons for this change in color preference are improved aesthetics, workspace lighting effectiveness, and cost savings due to decreased lighting requirements. To determine the impact of cabinet color choice on lighting effectiveness and the potential cost savings, the Panduit Corporate Research & Development team conducted a series of computer simulations.
Black cabinet surfaces absorb a high fraction of the illumination falling on them. By using lighter colors for the cabinets, more illumination is reflected into the room, increasing the overall lighting level. Fewer light fixtures are needed, resulting in a lower continuous lighting power load.
Baseline Configuration Model
For this evaluation, we used Autodesk Revit Architecture and MEP software with Lighting Analysts Elum Tools to create a virtual model of a 5,000 square foot (465m2) data center with a 12 foot (3.7m) high ceiling. Nine rows of twenty cabinets each were arranged in an uncontained hot aisle/cold aisle configuration as shown in Figure 1.
All of the aisles between the cabinet rows were 4 feet (120cm) wide, and the cabinets were 4 feet (120cm) deep. Light was provided by T8 fluorescent tubes in 2′ x 4′ (60cm by 120cm) fixtures installed in a suspended ceiling in line with the center of each aisle. The room’s floor and wall surface reflectance values were set to gray, and the ceiling to white. The measurement points indicated in Figure 1 show where illuminance in the model was measured.
Baseline Configuration Scenarios
Figures 2 and 3 show the baseline hot aisle/cold aisle models with black and white cabinets, respectively. For both scenarios, we measured the simulated light levels, or illuminance, at floor level and at 30 inches (76cm) above the floor.
Results of Baseline Configuration Analysis
Figure 4 graphs the illuminance, measured in lux, at each of the points indicated in Figure 1. (Lux is the international measure of light intensity on a surface. One lux is equal to one lumen per square meter.) The graph shows that the illuminance is lower in the centers of the hot and cold aisles and along the aisle by the end walls of the data center than it is at the ends of the hot and cold aisles.
The graph also shows that using white cabinets increases the illuminance in all areas measured, with a 56% increase in illuminance in the centers of the hot and cold aisles and a 32% increase in the remaining monitored areas.
Cold Aisle Containment Model and Scenarios
The study team created a second set of configurations by adding cold aisle containment to the baseline models, including end-of-aisle doors and a translucent roof for each cold aisle. The cold aisle containment models with black and white cabinets, respectively. For each of these scenarios, we measured illuminance at the same measurement points as for the baseline configurations. However, note that the “center of cold aisle” measurement point was within a contained cold aisle.
This study shows that using white cabinets instead of black cabinets increases illuminance, which means that a data center can be lit with fewer light fixtures. However, true optimization of illuminance is more involved than simply uniform reduction in the number of fixtures. Each data center has additional variables, besides those considered in this study, which can affect the results. For instance, the reflectivity of surfaces may be different than the values assumed for this study, the effects of white surfaces may not be uniform throughout the data center, and there may be lighting fixtures that cannot be removed. In the theoretical model, it became apparent that the distribution of light fixtures can be a limiting factor in several ways:
- The number of fixtures can only be adjusted by whole numbers
- The aisle lengths limit the number of fixtures that can be installed
- Fixtures installed too far apart result in uneven light distribution
The models and simulations for this study were used to estimate how costs can be reduced in the data center by using white cabinets. The Lighting Handbook, published by the Illuminating Engineering Society (IES), recommends illuminance of 100 lux for data centers, but it is more common for such facilities to be lighted to 300 lux. Therefore this study used 300 lux as the target value. In each of the data center configurations, the number of lighting fixtures in each cabinet aisle was adjusted until a minimum illuminance of 300 lux was observed. Table 1 lists the savings that were gained from not having to install as many lighting fixtures, and Table 2 lists reductions in operating expenses achieved by reducing the lighting electrical load.
Note: If timers or occupancy sensors that turn off lighting when not needed, or more efficient light sources such as LEDs are used, then the potential savings from reducing the number of fixtures are reduced.
Effects on Illuminance in Cabinet Interiors
White cabinets have another benefit over black cabinets. The higher reflectance of a white interior provides more illuminance inside the cabinets, resulting in better working conditions for technicians. However, the question still remains as to whether this is true if the room lighting is reduced.
To find out, one cabinet was modeled with the rear doors open and illuminance was measured inside the cabinet. This model did not include the effects of a technician standing at the rear door to perform work tasks.
The data shows that if white cabinets are used instead of black cabinets, but the room lighting level is not reduced, then illuminance inside the rear of the cabinet increases by 80%. However, if the room lighting is reduced to take advantage of the white cabinets’ higher reflectivity and to save on energy costs, then the illuminance inside the cabinet is only 16% higher. Unless the room is significantly over-illuminated, technicians most likely need additional task lighting to complete work inside either a black cabinet or a white cabinet.
Aesthetic Effects of White Cabinets
The aesthetics of data center cabinet color are extremely subjective. White cabinets make a data center look more contemporary, and they tend to show dirt less than black cabinets. However, in an effort to minimize lighting costs, a data center might have white or near-white walls, floor, and ceiling as well as white cabinets. Too much white in an environment creates a high level of glare and inadequate contrast, which can be hard on the eyes. However, if the space is not often occupied then this may not be a concern.