the quantity of electric light. The control
signal can activate two modes of operation:
(1) a simple on-off switch or relay, or (2) a
variable-output signal sent to a controller
that continuously adjusts the output of the
electric lighting.
Different photosensors are manufac-
tured for indoor or outdoor use. In the north-
ern hemisphere, photosensors used in
outdoor applications are usually oriented to
the north. This orientation ensures more
constant illumination on the sensor because
it avoids the direct sunlight contribution.
Wireless Remote Control
Radio-controlled systems
Some systems allow wireless remote control
and can interface to audiovisual and other
systems in both commercial and residential
applications.Radio-controlledsystems elim-
inate the need for wiring between the
sensor, processor, and controller. Radio
transmitters communicate with controllers
viaradiofrequency (RF) signals. Controllers,
in turn, regulate and adjust electric lighting.
These systems can employ multiple trans-
mitters for multiple-location control and
multiple controllers for multiple areas.
Radio frequencies from many sources
can interfere with proper operation of this
equipment, however. These systems are
also relatively expensive, but they are useful
where the controlled luminaires are difficult
to access. They are also suited to retrofit
applications where control wiring would be
difficult or expensive to install.
Infrared preset controls
Infrared preset controlsallow you to create
and recall settings for electric lighting the
same way you set and recall AM and FM sta-
tions on a stereo tuner/receiver. The hand-
held remote control sends an infrared (IR)
signal to wall-mounted switches and dim-
mers that have a receiving IR window. An
unlimited number of dimmers may be con-
nected in the same room.
Typically, infrared preset controls have
an IR range of up to 50 ft along the line of
sight. They use standard wiring and can be
retrofitted to replace switches or dimmers,
using the existing wires for installation.
Good-quality infrared controls will minimize
chances of interference from radio, audio,
and video equipment.Dimming Control
Adimmerprovides variation in the intensity
of an electric light source.Full-range dim-
mingis the continuous variation of lighting
intensity from maximum to zero without visi-
ble steps.
All dimming systems operate on one of
two principles for restricting the flow of elec-
tricity to the light source: (1) varying the volt-
age or (2) varying the length of time that the
current flows during each alternating current
cycle.Resistance Dimmers
Historically,resistance dimmers were the
first dimming method; they were used
mainly in theatres in the early part of the
twentieth century. A resistance dimmer, or
“rheostat,” controls voltage by introducing
into the circuit a variable length of high-
resistance wire. The longer the length of the
wire, the greater the resistance, the lower
the voltage, and the lower the intensity of
the lamp.
In order to absorb a sufficient amount of
energy, the resistance wire must be quite
long; for this reason it is often coiled. Current
flows into one end of the coil and an arm
slides along the resistance wire in incre-
ments. Dimming is thus achieved in a series
of steps, often a minimum of 110 to appear
“flicker-less.”ELECTRICITY