LIGHTING CONTROLS
Lighting control systems will become a permanent feature in the years ahead, due to the
contribution they make in reducing overall energy costs.
Basic ON/OFF solutions through the use of occupancy sensors are readily available and make
an immediate impact in reducing electricity costs.
Occupancy sensors, without human intervention, luminaires will automatically switch on or off,
based on the occupancy of certain areas.
Most types of sensors utilize multi technologies incorporating both Passive Infrared (PIR) and
Ultrasonic i.e. movement and sound. These sensors provide superior occupancy detection
compared to a single technology sensor.
Depending on the application a range of sensors from wall switching to ceiling mounted units
are available.
Passive infrared (PIR) occupancy sensors
PIR sensors respond to sudden changes in background heat energy by detecting the presence
of heat energy at a wavelength emitted by humans. They must be able to have a direct “line of
sight” to an occupant to detect his presence. A curved faceted lens defines the field of view as
a fan-shaped series of vertical and horizontal “cones” of detection projected from the sensor.
The further an occupant is from the sensor, the wider the gaps between these cones. Therefore,
the sensor’s sensitivity to motion decreases with distance away from the sensor.
Ultrasonic Occupancy Sensors
These sensors use a quartz crystal that radiates high-frequency (25-40 kHz) sound waves
undetectable by the human ear. These waves are emitted into the sensor’s field of coverage,
where they bounce off of objects, surfaces and people. When the waves bounce back to
the sensor, their frequency is measured. Motion is detected via a slight shift in frequency
(Doppler Effect), triggering an occupancy signal. Ultrasonic sensors can “see” around objects
and surfaces if the surfaces in an enclosed area are hard enough to bounce back the sound
waves for detection.
Dual-Technology Occupancy Sensors
Dual-technology sensors utilize both ultrasonic and PIR technology for maximum reliability and
coverage with a minimum of false triggers. Both ultrasonic and PIR signals are required to reliably
switch on lights and switch them off
Benefits:
• Cost effective use in cellular offices
• Effective in areas which are unoccupied for long periods of time, e.g. storerooms, cloakrooms,
toilets
• Additional security by switching on if intruders are detected in an otherwise unoccupied office
• Incorporates an adjustable time delay before switching luminaires off
• Controls a number of fluorescent luminaires up to 1500 Watts
To further reduce energy costs consideration should be given to daylight harvesting.
This can be achieved, depending on the application for either small or extensive lighting applications
through using DSI technology (Digital Serial Interface) or the DALI interface protocol (Digital
Addressable Lighting Interface) with the appropriate dimmable electronic ballast.
All of the above technologies can be adapted into a fully integrated Building Management System
(BMS) offering automatic control in addition to lighting, over air conditioning, security systems, blinds
and shutters, and audio/vision controls.
The requirement in South Africa is to reduce current electrical consumption by a minimum of 10%.
Lighting and lighting controls, offer between 25% - 75% in potential reductions on your lighting load,
is immediately implementable and often self funding from the financial savings achieved.
ENERGY
Energy is a basic unit for which the electricity utility (Eskom) charges.
In the case of a lighting system:
Energy consumed (kilowatthours) = power (Watts) x time (Hours).
We can reduce both the power (Watts) and the time (Hours) and hence the energy consumed
(kilowatthours) through maximising the technology available, i.e. electronic ballasts, occupancy
sensors or daylight harvesting.
If we can dim due to the availability of natural light or turn off the lights when occupants are
not present, we can reduce energy wastage up to 70% + on a lighting installation.
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