Dimmable lighting control has seen limited application in commercial buildings. However, due to two primary factors, adoption has grown. First, commercial building energy codes that require daylight harvesting have increased demand for lighting that could respond transparently in regularly occupied spaces. Second, light-emitting diode (LED) lighting’s installed base continues to grow, and a majority of LED products are dimmable, which creates new opportunities.

One such opportunity is task-tuning, also called institutional task-tuning and high-end trim. As its name suggests, this strategy involves reducing lighting based on Illuminating Engineering Society-recommended (IES) maintained task light levels for individual spaces rather than the originally designed maintained light levels, which may be higher than needed. The lighting can still be dimmed to implement other strategies, such as manual control and daylight harvesting, but the high-end is capped, resulting in permanent energy savings. With programmable scheduling, users can adjust the trim point by time of day.

Based on an analysis of 88 papers and case studies, a 2011 Lawrence Berkeley National Laboratory (LBNL) meta-analysis study of average lighting energy savings achievable with various lighting control strategies determined that institutional task-tuning can generate an average of 36 percent lighting energy savings. The LBNL grouped task-tuning controls with other options, including playing with ballast factor and installing group or lumen-maintenance controls.

Because this strategy trades light level for energy savings, it is ideally suited to overlighted spaces. This is more apt to occur with designs that emphasize generalization over individualization when it comes to matching light levels to application. As with other upgrade options, cost-effectiveness also increases with size of controlled load and number of annual operating hours.

Even then, the energy cost savings may not be sufficient to justify the cost of new dimmable lighting. That being said, task-tuning may be highly cost-effective where dimmable lighting is either planned or already installed, such as lighting controlled through daylight harvesting and LED general lighting. In this case, the cost of the task-tuning is largely the time required to measure light levels, communicate with occupants and adjust lighting controls. Therefore, the initial cost is incremental and easier to pay back through energy savings. If new LED general lighting is installed and operated by an intelligent lighting control system with high-end trim capability, task-tuning can be implemented with more flexible zoning down to the luminaire and individual task level, potentially maximizing energy savings.

Occupant satisfaction is the main unknown. While overlighting is not necessarily beneficial to visual comfort, occupants may react negatively to dimming light levels. For this reason, task-tuning may work best when implemented over time with incremental adjustments based on occupant feedback. The result can be an optimal balance of light level, energy savings and occupant satisfaction.

To evaluate task-tuning’s energy savings potential in Minnesota, the state’s commerce department engaged consulting firm Seventhwave, which measured energy consumption and task-light levels in 17 office, public assembly and education spaces in Minnesota and Wisconsin. The firm found these spaces to be overlighted, and it tuned light levels using existing dimming controls and based on measured and IES-recommended light levels. Then, it measured energy consumption again to generate estimates of savings and other useful information.

The researchers found that task-tuning produced an average of 613 kilowatt-hours of energy savings for every kilowatt of dimmable lighting, or about 22 percent of lighting energy. Energy savings varied 5–36 percent, depending on the space characteristics. In particular, energy savings tended to correspond favorably with overlighted spaces, large dimmable lighting loads, long hours of operation, lighting controls that weren’t commissioned, and lighting and control systems designed by a contractor and not a lighting designer or electrical engineer. However, audio/video spaces did not correspond to high energy savings with tuning, even though they are a traditionally popular application for dimmable lighting.

Since the controls were already installed, payback and return on investment were based on the incremental cost associated with the time to implement task-tuning. The researchers estimated the cost of task-tuning to be 3–6 cents per square foot in the studied spaces, generating a simple payback of 0.5–1.1 years. This reinforces the idea that task-tuning can be a cost-effective control strategy where dimmable lighting is installed or will be installed.

Task-tuning is a viable lighting control strategy that can be implemented with other control strategies for dimmable lighting. As dimmable lighting, particularly intelligent LED lighting, becomes increasingly adopted, task-tuning will continue to gain adoption as a means of producing energy savings in overlighted spaces.

For more information about the Minnesota Seventhwave task-tuning study, visit www.seventhwave.org/tasktuning.