Advanced Lighting For Office Open-Plan Office Applications High-Density 1 This High-Density 1 lighting application module presents alternative energy effective lighting design options for open-plan offices. These options provide lighting uniformity, glare control, daylighting and visual comfort all high priorities for office environments. Workers often spend a significant percentage of time in a given office space so it s important that these spaces are conducive to occupant health, comfort and productivity. With regard to lighting design, 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. Some important goals to consider: The ambient lighting source for the space is separated from the workercontrolled 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. Low partitions can increase the sense of spaciousness and the occupants connection to the windows, as well as utilizing lighting energy more effectively. An educational program should be in place to educate users of the functions and abilities of the lighting control system.
Approach Recessed High- Performance Lensed Luminaires lighting power density LPD =.64 W/SF Standard and.67 W/SF Dimming concept Open-Plan offices with high ceilings utilize recessed fixtures with broad distribution. Interior walls may receive light as well, potentially reducing the need for additional wallwashing. Adjustable desk lights may supplement illumination for tasks, and give users personal control and increased satisfaction. Lighting Concepts for recessed high-performance lensed luminaires in open-plan offices with high ceilings and low furniture partitions: Recessed luminaires provide ambient lighting. Articulated desktop luminaires provide higher light levels when necessary. Local control of task lighting promotes worker satisfaction. The lighting system has an orderly appearance but spacing may vary. Luminaires are spaced more closely over work areas. The selected luminaires distribute light to the vertical surfaces in addition to horizontal task surfaces. All vertical surfaces above 30" AFF are light-colored to increase brightness and inter-reflections. Recessed luminaires are most appropriate for open plan spaces with ceilings 8'4" or lower, since they do not illuminate the ceilings and have a greater potential for high angle glare. Suspended luminaires provide better quality for open plan ceiling heights above 8'-4". criteria Lighting Quality: Uniformity, glare control, daylighting and visual comfort are high priorities for office environments. Horizontal Illuminance (average maintained footcandles) on the work surface: 30-35 fc ambient, 45-75 fc for paper task performance Uniformity: Task-to-immediate surround: 3:1 preferred; 10:1 acceptable. Max-to-min in field of view: 10:1 preferred; 20:1 acceptable Lamp correlated color temperature (CCT): 3500K-4100K Color Rendering Index (CRI): 82 or greater for linear fluorescent Refer to IESNA DG-18 and IESNA Lighting Handbook 9 th Edition, Chapter 10 Design Guide matrix for more detailed information. Open Plan Office with a High Density of workstations, with high ceiling and low partitions, with recessed high-performance lensed luminaires. 2 Advanced Lighting for Office
Strategy Recessed High- Performance Lensed Luminaires lighting power density LPD =.64 W/SF Standard and.67 W/SF Dimming daylighting The combination of high ceilings and low partitions is the most favorable for daylight and electric lighting distribution, and provides more uniform illumination for less energy. Locate open-plan areas at building perimeter for greatest effectiveness of daylight harvesting controls. Proper sun shading is required. Provide clerestory windows, skylights, or roof monitors when offices are located on the upper floors. Control the lighting by zones that are consistent with the daylight distribution. Provide automated or motorized shade controls for open-plan spaces. luminaires a The luminaires selected for this application are recessed for use in low ceilings, and have a wide distribution to enhance the brightness of vertical surfaces for increased comfort. These luminaires use highperformance lenses and splayed sides and are significantly more efficient than those with open-celled parabolic louvers, reducing energy consumption and the quantity of luminaires needed for a space. b Same as luminaire A, except these luminaires contain dimming ballasts, providing continuous reduction of light down to 10% or lower of full output. These luminaires are used for daylight harvesting, are capable of reducing electric light in response to the availability of natural light, and are located less than 15' from the window wall, as shown on the plan. A B C c Task lights located on the desktop are articulated, i.e., allow adjustment in two or three axis to supplement the ambient lighting for demanding visual tasks and for any employee who is older than 40, wears corrective lenses, or simply desires more light. Maintenance Issues Super T8 lamps provide extended lamp life exceeding 30,000 hours, and the lumen output does not depreciate more than 5% over the rated life of the lamp. Ballasts with higher or lower Ballasts Factors may be considered to tailor the luminaires to the project. However, the same ballast should be used for all applications, or limited to specific areas, to prevent confusion during replacement or maintenance. The number of different types of lamps and ballasts should be minimized for ease of maintenance and to ensure that components are correctly replaced. LUMINAIRE SCHEDULE FOR OPEN-PLAN OFFICE APPLICATIONS Recessed 2-lamp 2'x4' high performance lensed troffer Direct wide distribution Non-planar curved or angled lenses (2) 32 watt T8 fluorescent lamp (F32T8/835) in cross section High Performance (3100 lumens) lamps, Low Mercury/Extended Life Electronic NEMA Premium instant-start ballast Same as Type A above, except with electronic dimming Ballast Factor:.88 (1) 2-lamp ballast, 2-wire or 0-10V 4-wire, 10% dimming ballast System Input Watts: 60 Mean Lamp Lumens per Watt: 87 LED desktop task luminaire with remote electronic power supply Articulated movement so that luminaire head is adjustable in at least two planes of motion (three planes preferred) Adjustable height and extension 10" to 20" Uniform pool of light 11"x17" minimum area in size (9) 1 watt LEDs, Initial lumens: 379 HIGH DENSITY1 CCT: 3500-4100K CRI: 80+ Ballast Factor:.88 System Input Watts: 55 Mean Lamp Lumens per Watt: 94 Minimum Luminaire Efficiency: 88% CCT: 3000-3700K CRI: 75+ Electronic Power Supply System Input Watts: 10.4 Mean System Lumens per Watt: 36 3 Advanced Lighting for Office
Controls Recessed High- Performance Lensed Luminaires lighting power density LPD =.64 W/SF Standard and.67 W/SF Dimming control strategies This module could be controlled by a variety of control options. Vacancy sensors are seen as a typical consideration, where luminaires are grouped into zones that are turned on by occupants using manual switches and automatically turned off when not in use by networked sensors. A more advanced option would be to add dimmable perimeter daylight zones controlled by photosensors to the vacancy sensors. The strategy featured below is a basic option that uses daylight dimming with photosensors coupled with the less granular On/Off control of a time clock. This option applies when occupancy is consistent through work hours. control strategies: scheduling, daylight harvesting In this basic option, lighting is automatically turned on and off based on a set occupancy schedule. Daylight control zones dim when possible, while occupants use manual switches to control their local lighting. Graphics and details support the design development. A time clock turns lights on according to a schedule, only when the space is occupied. During hours of occupancy, energy is saved through daylight harvesting. Consider digital lighting control, which enables remote programming while providing other advantages such as energy reporting and diagnostics and simple future integration of additional control strategies. The microprocessor-based CPU should be conveniently accessible to the facility operator to enable future programming changes. Override switches shall be located so that users can see controlled lighting. Photosensors may be connected to controllers via lowvoltage wiring or may be wireless. In some cases avoiding the need for power wiring by either using batteries or harvesting light energy in the space to generate the energy required to produce the signal. Time clocks should be programmed based on building operation hours. Override switches are available for after-hours building occupancy. 4 Advanced Lighting for Office
Design Parameters applying this module to your project The design modules shown in the ALG are intended to serve as examples of best practices in lighting for common spaces with typical conditions. They provide a starting point for design teams, but are not intended to replace the design team or process. See the Matrix of Variations below (end of section) for variations in module characteristics such as partition height, ceiling height, workstation density, task lighting, ballast factor, dimming ballasts, and resulting changes in connected load (LPD). parameters used to develop the design This lighting design was developed and modeled with the following parameters and assumptions. If these factors are different in your space, it will be necessary to make modifications to address the actual conditions. 9'-6" dropped ceiling, ACT, some GWB or plaster. 80% reflective. 42 high furniture partitions, opaque, with no overhead shelves or bins. Floors 20% reflective, matte finish (carpet). Full height walls 70% reflective. Walls around windows 80% reflective. Desktop 60% reflective. Ballast factor (BF): This vignette assumes normal BF ballasts (nominal 0.88) for T8 lamps. Light Loss Factor (LLF) for linear T8 luminaires, not including ballast factor = 0.84. Due to the low partitions, no undercabinet lights were assumed for this vignette. Due to the ambient light levels calculated for this specific vignette, it was assumed that 55% of the workstations were supplied with an articulated desk-top task lights. Task lights should be made available to any workers who request them. Critical factors that will require modifications from this design include room dimensions, spacing and height of the workstation partitions, lack of overhead bins or shelves, colors and reflectances of the surfaces. matrix of variations The first row (yellow) represents the module as shown, additional rows represent variations. Partition Ht Ceiling Ht Workstn Density* W/SF W/SF daylight dimming** % Task lights*** Notes 42" 9'-6" <100 sf 0.64 0.67 55% 1 42" 8'-6" <100 sf 0.64 0.67 55% 42" 9'-6" 100-150 0.56 0.58 85% 1 sf 42" 8'-6" 100-150 0.55 0.57 70% sf 64" 8'-6" 100-150 sf 0.63 0.65 100% 2, 3 Ballast Factor (BF) of T8 lamps: Normal NEMA Premium ballast and dimming ballast = 0.88. * Total area of open plan space (sf) divided by total number of work cubicles. ** Assumes dimming ballasts for daylight harvesting in zone 15 from windows. *** Percentage of workstations with desk top LED task lights (8W each). Higher percentage of task lights required. 1. High ceilings are preferred in spaces with windows for better distribution of daylight and potential energy savings from daylight harvesting. 2. High furniture partitions absorb more light and create shadows. Underbin LED lights (8W) are needed to reduce shadows. 3. High furniture partitions and low ceilings are the least efficient combination. 5 Advanced Lighting for Office
Quicktips Recessed luminaires with wide distribution characteristics can be spaced on wide centers. However, since they do not provide desirable light to the ceilings, their usage should be limited to those configurations with ceilings lower than 8'-4" AFF and partitions higher than 56" tall. The use of high furniture partitions is the least favorable for daylighting or electric lighting distribution. This configuration will always consume more energy. Consider using glass or translucent furniture partitions and lowering the partitions that are parallel to the window wall. More light is distributed perpendicular to the length of the luminaire, so the layout should be coordinated with the orientation of the computer monitors. Running luminaires with the long side parallel to the window wall will make the daylighting harvesting system more effective and less distracting. Light the perimeter walls in the open-plan space to increase the impression of brightness in the space, to improve visibility and comfort, and to add visual interest to the environment. Interior finishes must be very light in color for open plan configurations. Luminaires should have concealed labels indicating the correct lamp and ballast numbers for replacement. Incorporate lamp recycling into operating budgets. For more advanced lighting design information for open-plan offices, including daylighting, interior design considerations, controls, maintenance issues and operation, go to: http:// algonline.org/index.php?open-plan-office About New Buildings Institute ALG Online is one of the design guides offered by New Buildings Institute (NBI) through its Advanced Buildings suite of tools and resources. NBI is a nonprofit organization working to improve the energy performance of commercial buildings. The organization works collaboratively with commercial building market players governments, utilities, energy efficiency advocates and building professionals to remove barriers to energy efficiency, including promoting advanced design practices, improved technologies, public policies and programs that improve energy efficiency. NBI works nationally with offices located in White Salmon, Seattle and Vancouver, Washington. Visit us for more information about New Buildings Institute at newbuildings.org, ALG Online at algonline.org and Advanced Buildings at advancedbuildings.net. 6 Advanced Lighting for Office