LIGHTING BY CRAIG DILOUIE
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
For more information about the Minnesota Seventhwave task-tuning study,
Getting in Tune
Task-tuning brings light to recommended levels
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.
DILOUIE, L.C., a lighting industry journalist, analyst and marketing consultant, is
principal of ZING Communications. He can be reached at www.zinginc.com. I S T