Task tuning for lighting
The task of a lighting designer is to design a lighting system that provides just enough light for a building’s occupants to conduct
their daily tasks. For instance, someone reading a book typically requires more light than someone walking down a hallway. The
designer must generally err on the side of providing too much light rather than too little to avoid occupant complaints. Spaces can
be over lit due to fixtures selection, lack of photometric analysis, or for aesthetic reasons. Today’s dimmable lighting systems allow
building operators to reduce overlighting by task tuning the lights, adjusting light levels so that illuminance is appropriate for the
activity in the space.
Good task tuning begins in the design phase by laying out fixtures with respect to furniture and occupant behaviors within the
space. Once the lights are installed the lighting should be dimmed until the exact target light level is achieved. Task tuning has
the highest potential for energy savings in spaces with long hours of operation, noncommissioned lighting systems, and systems
designed by contractors. If dimmable lighting is already in place for daylighting or occupant comfort, then task tuning has a short
payback of 0.5 to 1.1 years.
Task tuning at 749 University Row
The building at 749 University Row is a highly energy
efficient, multi-tenant office building constructed in
Madison, Wisconsin in 2013. Two of the building’s tenants,
Seventhwave and Potter Lawson, conducted task tuning in
their space.
Seventhwave implemented task tuning throughout its
space in conjunction with daylighting (photosensor)
control. Typically, photosensors are associated with
daylighting, but they also provide task tuning capability
when there is no natural daylight. By selecting a good
illuminance target, lights should never reach full power
since lighting power is reduced linearly with illuminance
(see Figure 4). Seventhwave, an energy consulting firm, was
particularly aggressive with its illuminance targets. Based
on occupant feedback, Seventhwave was able to tune its
open office area to 17 foot-candles, the private offices to 20
foot-candles, and the conference rooms to 30 foot-candles
(all below IES target levels for an office). Individual task
lights improve occupant comfort for people who require
more light.
Seventhwave also incorporated personal tuning in its lighting
controls. Personal tuning allows the lights to be adjusted
to an individual’s desired level instead of tuning broadly
across an entire office or space. Seventhwave used a hand
held lighting controller that allowed one user to select
illuminance levels and high end trim for each lighting zone
(see Figure 3). Personal tuning increases occupant comfort
but typically involves more complex controls—in this
case Seventhwave used digital, individually-addressable
fixtures. Light levels were adjusted upward in work areas
where people required higher illuminance.
Figure 1: Seventhwave’s office
Task tuning was also used in a large conference room
designed to be split into two smaller rooms with a movable
room divider. Six rows of lights would have been sufficient
lighting for this space but one row would have been directly
over the divider. An additional row of lights was added on
each side of the divider to address this problem, resulting
in an over lit space. These lights were programmed with a
‘high end trim’ of 70 percent of their full power when they
were installed. As a result regardless of occupant behavior
or daylighting controls these lights never exceed the
original target light levels.
After task tuning was complete, overall lighting power
density dropped from the installed 0.72 W/ft2 to 0.52 W/ft2.
For reference this is nearly half the 1 W/ ft2 lighting power
density required in offices by the IECC 2009 energy code.
(continued on reverse)
GS2153 2/12/2016
printed on recycled paper
your community energy company
behavior or daylighting controls they
would never exceed the original
target light levels.
scene was selected most often, but
because occupants were able to adjust
improving satisfaction.
Lighting
level
Annual
energy
savings
Cost
Incentive
Payback
period
ELECTRIC ILLUMINANCE (fc)
ELECTRIC ILLUMINANCE (fc)
creating a default scene that
ENERGY SAVING AND COST OF TASK TUNING IN SEVENTHWAVE’S
RELATIONSHIP BETWEEN POWER AND ILLUMINANCE
After task tuning was complete,
dimmed the lights by 32
POWER REDUCTION
Lighting level
Cost
Payback
overall
lightingAnnual
power density
went Incentive
percent to meet target light
reduction
energy
period
2
from the installed 0.72 W/ft to 0.52
60
levels. The default scene
2. For reference
$740 this is almost
$1,000 halfNot currently
1.4 years
W/ft29%
is selected most often,
but
G
available
50
NIN
the 1 W/ ft2 lighting power density
TU
MEASURED
occupants are able
to adjust
required by this project’s energy code
For Seventhwave’s space, it took approximately40four hours
light levels if needed. The
IECC 2009. The table below shows
RECOMMENDED
to become familiar with the lighting system, six hours to
average measured power
the payback associated with just the
30
actively tune 10,000 ft2, and two hours to adjust to occupant
reduction in the conference
added time taken to tune a dimmable
satisfaction. An occupant comfort survey found 20the majority
room is 24 percent. Tuning
system. For Seventhwave’s space,
of employees were satisfied with light levels after tuning.
allowed an aesthetically
it took approximately four hours to
pleasing
fixture
10
ELECTRIC
LIGHT layout while
become familiar with the lighting
minimizing energy usage
system, six hours to actively tune
0
Figure 3: Seventhwave’s
hand held
Seventhwave’s
hand-held lighting
and improving occupant
10,000 ft2, and two hours to adjust to
0
100
200
300
400
500
controller.
lighting controller
satisfaction.
LIGHTING
POWER (W)
occupant satisfaction. An occupant
comfort survey found the majority of
employees were satisfied with light
POWER REDUCTION
OTHER BEST PRACTICES 60
• Set target light levels in space
levels after tuning.
using: design specifications,
the IES
NG
• Start considering task tuning
in
50
NI
TU
handbook, or occupant
orMEASURED
facility
ENERGY SAVING AND COST OF TASK
the design phase. In addition to
TUNING IN SEVENTHWAVE’S SPACE
manager feedback.
incorporating dimming, the 40
lighting
designer should coordinate fixture
30
layout directly with furniture layout.
This will make tuning substantially
20
easier than with a general ambient
10
strategy.
RECOMMENDED
• Occupant feedback ensures
comfort and though it may reduce
29%
$740
$1,000
Not
1.4
the aggressiveness of tuning, it is
currently
years
likely to ELECTRIC
result LIGHT
in less complaints and
available
undoing of tuning down the line. The
0
Figure 2: Potter Lawson’s conference room
occupant may even suggest they are
• Savings from tuning alone are
not 100
0
200
300
400
500
comfortable with tuning beyond the
sufficient to justify the cost of dimming. LIGHTING
POWER (W)
Potter Lawson has a large conference roomHowever
that, for if combined with the benefits
target. Also consider following up
aesthetic reasons, has five light fixtures when
four
would
with occupants at a later date to make
of daylighting and occupant comfort,
Figure 4: Relationship between power and illuminance
sure they are still happy.
have been sufficient. Potter Lawson tuned or
this
space
by
simply inherent in the fixtures
(increasingly true with LEDs) then
OTHER RESOURCES
tuning can be justified •
onSolicit
a project
occupant feedback on the tuned light levels.
[1]how
Scottaggressively
S’s Task tuning
MN Card
• Integrate task tuning in the building design
phase.
While
quite
easily.
Although it may reduce
the lights
are tuned,
report
savings from tuning alone are not sufficient to justify the cost
it generally results in fewer complaints and greater likelihood
installation,
of a dimmable lighting system, the benefits •ofAfter
daylighting
and untuned
that thelight
tuned light levels will be maintained over time.
Williams, et al. 2012. “Lighting
levels
should
be
measured
using may even [2]
occupant comfort, or simply having dimmability inherent to the Occupants
suggest they are comfortable with lower
Controls
in Commercial Buildings,”
a light
meter.
is important
to than the tuning target.
fixturesLawson
(increasingly
true with
LEDs) can easily
justify
the It
cost
Potter
had a large
conference
light levels
Follow up with occupants at
Vol.
8,
No.
3, January 2012, pg.
measure only artificial alight
of tuning.
room
that, for aesthetic reasons,
later(excluding
date to make sure they are still happy.
161–180.
daylight). If possible, tune at night.
included five light fixtures when light
• Coordinate fixture layout directly with furniture layout
Other resources
to make tuning easier than if following a general ambient
[1] Schuetter, S., Li, J., & Lord, M. (2015). Adjusting lighting
strategy.
levels in commercial buildings. Retrieved November 24, 2015,
• Use design specifications, the IES handbook, or occupant
from www.seventhwave.org/tasktuning
or facility manager feedback to set target light levels for the
[2] Williams, et al. 2012. “Lighting controls in commercial
space.
buildings,” Vol. 8, No. 3, January 2012, pg. 161–180.
• Use a light meter to measure untuned light levels once the
lights are installed. It is important to measure only artificial
light (excluding daylight). Tuning (adjustment) of light levels
can immediately follow.
Making task tuning work
Written by Seventhwave.
Visit seventhwave.org.
For more information, contact an
MGE Business Representative at 608-252-7007.