Open-Plan Office Applications
Last Update: February 14, 2011
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Open-Plan Office Design

Lighting uniformity, glare control, daylighting and visual comfort are high priorities for office environments. The perception of natural color rendering and appropriate facial modeling contribute to effective worker interactions. Vertical illuminance on wall and partitions enhances the impression of brightness in the environment. The lighting should be interesting without creating distractions such as shadows, high contrast, or sudden changes in light levels.

Each of the following modules shows alternative ‘energy effective’ lighting designs for open-plan offices. These are only a sampling of valid approaches, but each adheres to the following goals for open-plan lighting:

  • The ambient lighting source for the space is separated from the worker-controlled task lighting. This can be accomplished using one luminaire with separate compartments, or by using one luminaire type for ambient light and a local task light at the desk.
  • The ambient lighting should enhance orientation and continuity, unifying the space while still allowing variations in functions and layouts. Ambient lighting should be generally uniform to enable flexibility within open-plan work areas.
  • Circulation aisles within open-plan areas are typically fixed even if workstations change over time, so light levels may be lower in these areas and tailored for the function.
  • Vertical surfaces should be illuminated because they contribute to the occupants’ sense of brightness in the space, and their visual adaptation level.
  • Window brightness should be balanced by light-colored finishes and lighting on the interior-most walls. 
  • Overhead bins and shelves cause harsh shadows that create excessive contrast, so these shadows should be mitigated with local undercabinet lighting or wide-distribution luminaires.
  • Visual interest can be created by enhancing architectural features, focusing on art work, or using decorative luminaires.
  • Local control of task lighting promotes higher worker satisfaction. However, the control of the ambient lighting system should not be given to the individual workers.  Instead, the ambient system should be controlled in large enough zones to create a consistent visual field of light within the room as a whole.
  • Controls should be designed to minimize distraction. The light over one workstation is in the field of view of other workers, and is often providing ambient light for surrounding workstations.  Individual workers’ control of the lighting should be limited to only that portion that affects their own workstation.
  • Low partitions can increase the sense of spaciousness and the occupants’ connection to the windows, as well as utilizing lighting energy more effectively.
  • At the interior perimeter walls of the open-plan space, the luminaires providing ambient light may also provide important vertical illumination on the walls. 
  • Supplemental wall-washing may often be necessary to provide adequate illumination on the interior vertical surfaces.
  • An educational program should be in place to educate users of the functions and abilities of the lighting control system.

Daylighting

The open-plan areas should be located at the building perimeter to maximize the effectiveness of daylight harvesting. Side lighting (vertical windows) that also provide the occupants with views to the outside are preferred, but top lighting (skylights or clerestories) can be effective for bringing the daylight deep into the interior of buildings. Daylighting from multiple directions generally reduces contrast and increases visual comfort. Proper sun control maximizes the available daylight during times when direct sun is not on the windows, while preventing excessive heat gain and glare. Exterior sun control is more effective from a thermal and energy standpoint as it prevents unwanted heat from entering the building.  If exterior sun control is not present or sufficient, interior blinds or shades should be automated in open-plan areas to enable daylighting by retracting whenever sun control is not required. The ALG Daylighting chapter has a section on shading strategies, look for it in Fenestration Technologies.

Daylight should be utilized as the ambient light source for work and circulation areas and should be supplemented by worker controlled task lights. Consider exterior or interior light shelves to reflect the natural light onto the ceiling and deeper into the space. Electric lighting should be controlled in patterns (zones) that are consistent with the daylight distribution. 
 
Interior Design Considerations for Open-Plan Offices

Not all the energy savings goals can be met by lighting equipment alone. The design of the building envelope and fenestration has the largest impact on lighting energy savings, followed by interior design decisions. The following recommendations will not only decrease energy consumption, but will also lead to higher quality visual environments: 
 

  • The higher the ceilings, the farther the daylight can penetrate into the space, and the more effectively the electric lights can distribute light over partial-height partitions.
  • The lower the workstation partitions, the more efficiently daylight and electric light can be distributed into the space, requiring less energy consumption.
  • To increase daylight penetration and views, all the workstations within 25’ of the windows should be low (48” or less) to give more occupants a connection to the out-of-doors, and to maximize the effectiveness of daylighting.  If taller partitions must be used, they should be oriented perpendicular to the window wall.  Consider clear or translucent panels throughout, but especially for the workstations nearest to the windows.
  • Overhead cabinets not only block ambient light from the ceiling, but create shadows that need additional luminaires and energy to mitigate.
  • Locating all the computer monitors facing parallel to the luminaires and the window wall, provides greater opportunities for glare control. Computer monitors located in a corner of the workstation have a much higher potential for reflected glare since they will receive light from luminaires oriented either parallel or perpendicular to the workstation. They should be movable so that the occupant can orient them for their own greatest comfort. In particular, newer monitor technologies have reintroduced the shiny screen, prone to reflected glare.
  • Interior finishes are an integral element in energy efficiency and in visual comfort for office workers. The surfaces surrounding the windows and on the ceilings must be the lightest of colors (80-90% reflective). Work surfaces and vertical partitions, bins and walls above 30” should also be light in color (min 65% reflective). All these surfaces should be matte or eggshell in finish.
  • Determine the percentage of the working hours that could be daylighted versus non-daylighted. This may be a deciding factor when designing workstation layouts, computer monitor locations, and even when selecting luminaires and control strategies.

Maintenance Issues

  • Linear fluorescent lamps, especially 4’ long higher performance (“super”) T8 lamps and ballast systems, are the most efficient source for ambient office lighting. These systems have very long rated lives and are readily available through distribution. Ceramic metal halide and compact fluorescent lamps are most effective for accent lighting or low light levels. These sources can significantly reduce energy and maintenance as compared to tungsten halogen or incandescent sources. It is best to design with the fewest different lamp types possible, to minimize stocking and replacement errors. Luminaires should be cleaned on a regular basis to avoid loss of light from dirty surfaces.

Controls for Open-Plan Offices

General
The control strategies listed below can be used in combination with the other design strategies to achieve the greatest energy savings. Occupancy times and patterns should be understood before finalizing control system design. The designation of luminaires to separate control zones is an important step in achieving flexibility and successful energy savings.

Daylight Dimming
Properly commissioned dimming ballasts and photo-sensors can dim luminaires near windows and under skylights when sufficient daylight is available. “Demand reduction” can be accommodated (but should be limited within work areas to avoid negatively impacting occupant performance.)

Vacancy Sensors
Electric lighting should require manual-on operation, turning lights off automatically when the space is vacant. In open-plan areas, consider ceiling mounted ultra-sonic sensors that can detect motion within cubicles, coupled with manual ON electronic wall switches. Zones should be reasonably large (750-1000 sf) so that the environs are lighted even when only a few occupants are working, but small enough to achieve savings. Timeclocks (time switches) may keep lights on during peak occupancy hours, but pass control to the manual ON sensors during regular lunch times and again toward the end of the workday when low occupancy is anticipated. Infra-red sensors within cubicles can be used to turn off under-cabinet lights, desk top task lights, “workstation specific” downlighting and some plug loads.

After Hours Switching
Decorative lighting and wallwashing that does not contribute to occupant performance can be switched off after normal hours of occupancy. It may be possible to turn off some luminaires in open-plan circulation or lounge spaces. This can be accomplished with dimming, bi-level switching, or keeping lights at full brightness only in parts of occupied zones.

Evening / Nighttime Dimming
If electric lighting is used to compensate or balance high levels of daylight, lighting can be dimmed or switched during evening and nighttime hours when occupants’ eyes are adapted to lower luminances. Demand reduction can be accommodated, but is needed less after peak afternoon hours.


Maintenance and Operation

  • The high performance (“super”) T8 lamps have characteristics that provide long term operational and maintenance savings to the owner, such as extended rated life and higher end-of-life light output. Economies can be had by ordering these lamps in advance in bulk, rather than buying standard T8 lamps without these advantages off-the-shelf at a local hardware store
  • For wall accent: CMH appears white during normal life. As lamps reach their end of life, they shift to hues of blue, pink, green, or other colors. This is a good indication that lamps are about to fail and needs to be replaced.
  • Group re-lamping may not be the best recommendation for the latest generation of high performance (“super”) T8 and T5 fluorescent lamps with high lumen maintenance and extended lamp lives, when used with advanced controls. The operation of lighting controls beyond simple timeclocks, varying usage due to occupancy, daylight and user intervention, makes it more difficult to determine the actual operating time of any specific lamp. While it saves labor costs to re-lamp (replace) all of the lamps at the same time, this benefit is overridden by sustainability concerns: Group re-lamping has the potential to waste materials by discarding many lamps with significant life and output remaining. Where re-cycling is not mandated, it puts more materials in the waste stream, some of which are toxic. However, group re-lamping is justified when significant increases in energy performance can be achieved by a future generation of lamp technology.
  • Due to the mercury content of fluorescent, CFL and CMH lamps, (even those of the low-mercury type), lamp recycling should be incorporated into operating budgets, along with storage closets dedicated to holding used lamps prior to recycling.
  • The specifications should call for a maintenance and operating manual to include product, replacement and troubleshooting information for all lamps, ballasts, luminaires and control equipment. Specify a reasonable number of spare lamps, ballasts and components to support the maintenance efforts.
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