Because of recent federal and state energy legislation, energy-efficient lighting is now a major component in the effort to reduce the load and increase building energy savings. Since lighting accounts for more than 30% of electric energy use in offices, lighting controls are going mainstream. However those office lighting control systems should still be flexible enough to provide the proper illumination for different tasks and respond to changing conditions within the space.
Today's workplace is exceedingly dynamic, with employees shifting among a variety of tasks during a typical day. A high light level is needed for reading documents with small text or engineering drawings, a medium light level is more appropriate for collaborative meetings, and an even lower level is required for keyboard tasks at a computer. Additionally, each employee's personal light requirements may differ based on age, vision, or preference.
Thus, quality light — illumination that can be described as comfortable in all office facilities — is important because it brings tangible returns. And that may include giving the light users more control. According to many recent studies, employers who offer individual workstation control, particularly for lighting level and thermal comfort, have happier employees, improved work output, better employee attraction and retention, and financial success.
Getting a solid return on your investment. Believe it or not, job satisfaction and employee retention as they relate to comfortable office lighting can have a measurable effect on your bottom line. According to Harris Rothenberg, LLC, a New York City-based performance consulting firm, replacing an employee costs 1.2 to 2 times their annual salary due to organization inefficiency while the position is vacant and the processing costs related to the new hire. The same research indicated that a new employee reaches maximum efficiency and performance only after 13.5 months of employment.
More specifically, surveys conducted in office settings over the last few years indicate the value of having personal controls at the workstation. For example, a landmark productivity study published in 2003 by the Light Right Consortium linked the availability of workstation personal control to worker satisfaction and performance. Nine office workers in Albany, N.Y., were subjected to a variety of lighting scenarios and then asked for feedback. When the questionnaire results were evaluated at the end of the test period, the Light Right Consortium found that the availability of lighting control in the workplace directly affected the workers' motivation on the job.
Thus, some facility owners are willing to pay a premium for personal lighting control to achieve a gain in worker satisfaction. In these situations, the occupants are able to “tune” the lighting according to changing tasks, their mood, and the amount of daylight available. For these reasons, tailored lighting has the capacity to provide a significant return on investment.
Understanding workspace-specific lighting. In the past, fluorescent luminaires consisted of a light source (lamp), a reflector or lens, and a ballast to operate the lamps. However, a variety of new occupancy sensors, photocells, and infrared/RF controls are now being mounted in fluorescent fixture housings to allow “fine tuning” of the lighting in an office space. With motion detectors and daylight sensors that are either remote-mounted or integrated into a luminaire housing, lights will dim and/or switch off when not needed. Depending on the technology selected, sensors may be programmed using an IR remote controller or administration software.
At least two manufacturers offer a suspended linear fluorescent luminaire with the features described above. The three-lamp, direct/indirect luminaire integrates occupancy sensing, daylight sensing, and personal dimming, which can be accessed remotely using a network communications system. Two four-foot T8 lamps and a program-start dimming electronic ballast (64W active power) provide the direct/task lighting. A single T8 lamp operated by a program-start electronic ballast (31W active power) provides the indirect light component.
This type of fixture is called a workplace-specific luminaire, since a single unit can be installed over an employee's cubicle or private-office desk. While the workspace-specific fixture is more expensive than a standard T8 fluorescent luminaire, it allows a designer to achieve task-appropriate illumination with reduced energy use. For example, a typical 10-foot by 12-foot office may be illuminated with a pair of two-lamp or three-lamp fluorescent troffers. Assuming the use of T8 lamps and electronic ballasts, the power density will be about 1W to 1.5W per square foot. However, you'd only need to specify one three-lamp direct/indirect workspace-specific luminaire to achieve up to a 50% reduction in power density.
In an open-office area, workplace-specific lighting can also reduce the number of fixtures required, compared to a uniform spacing of the fixtures.
Workspace-specific, controllable luminaires allow a building manager or engineer to tailor the sensor response to follow a specific pattern. Consider, for example, a typical situation during the work day: if the integral occupancy sensor of the workspace-specific luminaire doesn't detect movement at the cubicle desk directly below, the downlighting will automatically dim to off. Only the uplighting component of the luminaire remains on. Outside of the regular office hours, an occupancy sensor in the luminaire (or elsewhere in the open office) can be set to control both the uplighting and downlighting component of the suspended luminaire.
The higher initial cost of a workspace-specific controllable luminaire is an important factor in a new or retrofit project. However, due to ease of installation and a reduction in the number of fixtures required, the luminaire can be price-competitive with a parabolic troffer system on an installed-cost basis and provide enhanced quality of illumination and appreciable energy savings over the system's life.
Lets look at some personal control products that operate separate from the workspace-specific luminaire.
One type of dimming system allows a worker to control the overhead fluorescent lighting fixtures using a handheld remote IR control. An IR receiver/sensor connected to the dimming ballast provides the control to change the lamp's lumen output.
Another lighting system features a manual override of automated fluorescent lighting settings through use of a wall-mounted control, an infrared handheld remote control device, or a PC workstation. The system can also factor in available natural daylight, a technique known as daylight harvesting. This strategy uses ceiling-mounted photocells to measure the changing contribution of daylight and then compares this light level to an established level of light in a room. The controller responds by dimming or brightening the fluorescent lighting to sustain the desired level. The controller is compatible only with specific manufacturer's electronic fluorescent dimming ballasts. Usually, as more are approved, they're added to a manufacturer's list.
Yet another system combines fixtures, user controls, and digital communications. Instead of controlling groups of fixtures by circuit, groups can be established by address and controlled with a group controller. Wall control options range from simple group dimmers or broadcast controls to programmable scene controllers.
Computer control software is also available that supports digital controllable ballasts in ceiling-mounted fixtures. System features include individual occupancy control of assigned fixtures, standard lighting control functions, logging of fixture operating levels (energy consumption calculation), and reporting of lamp and ballast failures.
Ballast manufacturers are also responding to the expanding role of fluorescent dimming systems by offering 100% to 5% dimming of T8 lamps. This type of ballast is compatible with standard 1-10VDC fluorescent controllers and compatible with two-wire power line fluorescent dimmers, making it ideal for individual office lighting or automated building applications.
The indoor office environment has changed considerably over the years. Flexible workspace designs, computer equipment, and an aging workforce have presented new challenges to lighting designers and installers. And further complicating the situation, studies have shown that lighting has a direct effect on employee morale and productivity. But for lighting professionals willing to get “personal” with their designs and offer light users individual control over brightness, modern office lighting is a little less intimidating.
Sidebar: Fluorescent Dimming in Triplicate
Fluorescent lamp dimming that uses electronic ballasts is done in three ways:
0-10VDC analog, phase control analog, or digital control.
0-10VDC — This analog control system is the most commonly used technology today. Groups of fixtures are connected to the control circuit to receive the same command signal, allowing the control to extend beyond a single power circuit layout.
Phase control technology — This is ideal for an architectural lighting scheme in a smaller space, such as a conference room or an individual office. Generally, a phase control dimming ballast uses the same pair of conductors for power and control, thus providing for a simple cost-effective retrofit where control from a single location is desired.
Digital control system — Rather than sending a variable analog control voltage to the ballast, this sends digitally encoded pulse signals that are free from noise or radio frequency interference, improving signal reliability and control flexibility. Many industry professionals envision the time when all building systems — lighting, HVAC, envelope systems, security and life safety — are integrated, from the smallest device and sensor all the way to the Internet, through digital communications protocols.