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500W – 1000W Tungsten Halogen floodlights with an efficacity
of up to 20 lm/W are conventionally used for external lighting
on construction sites.
These can be replaced by High Pressure Sodium
lights (SONS) providing an equivalent illuminance. The high
efficacy and very long life (20,000 hours average lamp life) of
these lamps make them ideal for floodlighting and for
illuminating external areas. High Pressure Sodium lamps have an
efficacity of up to 140 lm/W. [1] Hence a 180W SON would be
suitable for replacing a 1000W halogen flood light. However,
SONS are not designed for frequent switching due to their
start-up time between 1.5 and 6 minutes. [2] Thus, they cannot
be used with automatic presence detectors.
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A problem
occurring on many construction sites is external lights are
switched on during the day with nobody being aware of the amount
of energy wasted. Therefore, lamps installed for external
lighting should be controlled by a photocell to ensure the lamps
are only on when it is dark.
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Since external lighting is only provided to
ensure that someone entering the site by night will not be
injured, the use of occupancy sensors could furthermore reduce
the time external lights are switched on. However, it might
occur that an intruder enters the construction site in such a
way the occupancy sensor will not detect the person. The use of
PIR sensors for night lighting, therefore, depends on the layout
of the construction site.
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External
lights left on during the day
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During this investigation,
which involved researching manufacturer websites as well as local DIY stores, it
became obvious that the following external light fittings would be suitable in
order to reduce the energy demand for external lighting on construction sites.
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1.- 250W
Sodium Floodlight with Photocell control
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This floodlight
incorporates a night sensor that automatically switches on the light
at dusk each evening. The light will remain constantly switched on
throughout the night and automatically switch off again at dawn.
Thus, having lights turned on by day is automatically avoided, which
can save about 40% of the energy used for external lighting.
A 250W Sodium lamp
provides a light output equivalent to 1400W tungsten halogen light
but at approximately one fifth of the running cost.
Price:
£120
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2.-
500W fully Auto
Passive Infra Red (PIR) Floodlight
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This
halogen floodlight will illuminate at night each time the integral
PIR sensor detects a movement. During the day the built-in photocell
saves electricity by deactivating the floodlight.
The
price of Halogen floodlights incorporating a PIR sensor depends on
the detection angle and maximum reach of the sensor.
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Detection angle |
Maximum
reach |
Maximum
time switch |
Price |
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Medium
size |
110º |
12m |
12min |
£9 |
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Super
size |
240º |
20m |
na |
£70 |
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Lamp properties for
two different lamp sizes
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Replacing 1000W
Halogen lights by 250W SONS with photocell control can reduce the energy demand
for external lighting by around 80%. This is estimated by assuming that the use
of the photocell control will reduce the period external lights are switched on
from 18h per day down to 12h per day.
Replacing a 500W
Halogen lights by 500W Halogen lights with PIR sensors and photocell can reduce
the energy demand for external lighting by approximately 75%. This is estimated
by assuming that the use of the PIR sensor and photocell control will reduce the
period external lights are switched on from 18h per day down to 4h per day.
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(1)
Energy Saving Trust, Energy Efficiency
Best Practice in Housing – Energy efficient lighting; March 2004
(2)
Randall Thomas,
Environmental Design – An Introduction for Architects and Engineers, Second
Edition, published by Routledge
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