98 ELECTRICALCONTRACTOR | SEP. 14 | WWW.ECMAG.COM
tric light levels fall and rise to maintain a constant light level,
thereby saving energy.
Step dimming typically involves one or several output levels with the transition either being abrupt, as in switching, or
a smooth fade. Step dimming is well-suited for applications
where we want a smooth fade to a preset output level, such as
for demand response. It also works for bilevel switching but
without changing out alternate ballasts, lamps and luminaires.
A good example is light-level reduction in an HID or induction
luminaire during times when the space is unoccupied.
These inputs and outputs can be combined to achieve
unique lighting control strategies suited to addressing visual
needs, energy management needs or both. Manual control is
fairly well understood, so we’ll focus on automatic control.
Typically, with automatic control, lighting is reduced to save
energy in response to occupancy, a time event or daylight level.
Manual and automatic control strategies can be enacted using
the same control system by networking controllers with multiple input devices.
Occupancy sensing: This proven strategy involves reducing lighting use during periods when a space is unoccupied,
saving energy by minimizing waste, using occupancy or
vacancy sensors. The Lawrence Berkeley National Laboratory’s (LBNL) best estimate of average lighting energy savings
is 24 percent.
The input for “on” operation may be manual (manual-on
occupancy sensor or vacancy sensor), automatic (occupancy sensor) or both (auto-on to 50 percent output). The input for “off”
operation is automatic; following a designated period of time
after the sensor detects a lack of occupancy, it turns the lights
off. However, a manual-off override option may be available.
The output may be switching or dimming. In interior
applications, typically the lights are turned off, though for
applications that are intermittently occupied, the lights may be
switched (e.g., two fluorescent lamps in a stairwell luminaire)
or dimmed (e.g., continuous dim to off in an overhead luminaire
in an open office or step dim to a lower level for a high-intensity
discharge parking-lot luminaire).
Occupancy sensing is highly suited to smaller, enclosed
spaces that are intermittently occupied, such as private
offices, classrooms, conference rooms, copy and break rooms,
restrooms and other spaces. It is also frequently applied to
parking lots and area lighting applications, wallpacks, stairwell luminaires, warehouse aisles, and lighting within or over
workstations in open offices.
Time scheduling: This proven strategy involves reducing
lighting use during times of the day when illumination is predicted to not be needed. The LBNL estimates average lighting
energy savings of 24 percent (lumping it in the same category as
occupancy sensing, though it is arguable that occupancy sensing typically results in higher savings by being more precise).
The input for “on” may be manual or automatic, while the
input for “off” is automatic, usually combined with a manual
on/off override. The automatic input is typically a signal from
a physical timeclock, timeclock software intelligence built
into a control system, or some other building system, such as
a building automation or security system. The output may be
switching or dimming, depending on whether some light is
needed during unoccupied periods or whether the light source
cannot return to full output quickly.
Time scheduling is suited to larger, open spaces that are
regularly occupied and spaces that are intermittently occupied
but where the lights must remain on all day for safety/security
purposes. Local override (time extension) manual wall controls
are often installed to allow for irregular use of the space.
Another method related to both time scheduling and occupancy is the timer switch, which turns off the lights if a set
period of time passes after a person enters a room. This type
of control device is suited to applications such as utility and
Daylight harvesting: This strategy involves raising or
lowering output to maintain a set light level based on daylight
contribution. As daylight rises and falls, the electric lights lower
> FOCUS LIGHTING CONTROL STRATEGIES
Continued on page 100 →
Figure 2: The automatic time-based control in our sample
open office space must have the capability for local override to
account for irregular use of the space. Manual controls enable
users to override the shutoff in their local area.
Scheduled automatic shutoff (timeclock)
Override zones ( wall switches)
Scheduled automatic shutoff (timeclock)
Figure 1: In this open office space, the lights can be turned off
every night using an automatic time-based control and can be
grouped as a single zone.
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