Untitled - Journal of Lighting Engineering

Aleksandra KOSTIC, Bojana STANKOVIC, Aleksandra KRSTIC-FURUNDZIC
their operation can be programmed by
defining the luminaire voltages for different
time periods (regimes) during the operation
hours of public lighting. The device is
usually programmed in a way that it
provides voltage close to the rated one in
the evening hours (highest car and
pedestrian traffic densities) and lower
voltages in late night hours. Most often two
regimes with reduced voltages (luminous
fluxes) are programmed, with the usual
reduction of light of about 25% and 50% [3]
(since both car and pedestrian traffic densities
are significantly lowered in late night hours,
these reductions of luminous flux generally
do not jeopardize traffic safety).
A diagram that shows how both
luminaire luminous flux and power depend
on voltage represents the basic
characteristic of the devices for continuous
light control. Such a diagram is presented in
Figure 1 [4], where both curves are shown
for a case of a high-pressure sodium
luminaire.
As seen in Figure 1, the luminous flux
reduction of 25% is achieved at a voltage of
205 V (the power reduction is 20%), while
the luminous flux reduction of 50% is
achieved at a voltage of 178 V (the power
reduction is 42%). It should be mentioned
that our tests showed that public lighting
installations with high-pressure mercury or
metal-halide lamps are characterized by
slightly lower power reductions and,
therefore, provide less energy savings.
During spring of 2011, a pilot project
was conducted in Belgrade, in a street with
32 luminaires with 150 W HPS lamps, with
the aim of determining the numerical
indicators for possible energy savings by
30
applying several regimes in public lighting.
Programming of the device for continuous
light control was done in the following way:
- from the time of turning on the lighting
installation until 10iPM the illuminance level
was 10% lower than the one existing before
the device had been installed (this is justified
because the light level tolerance equals 10%
and the streets are usually overlit),
- from 10iPM to midnight the illuminance
level was reduced by another 25% (32% in
total), and
- from midnight to the time of switching off
the lighting installation the illuminance
level was set to 45% (0.9×50%) of the one
existing prior to the device installment.
The pilot project, which lasted for 30 days,
showed energy savings of 31.6%. Taking
into account the fact that throughout the
year there is a change of timing for public
lighting switching on and off, this project
also showed that the annual energy savings
would be 30%.
4. Influence of the application of devices
for continuous light control on the
reduction of CO2 and methane emissions
Since about 110,000 luminaires are
installed in the Belgrade public lighting,
with the total power of around 20 MW, the
possible annual energy savings amount is
30%×20 MW×4000 h = 24,000 MWh (the
Belgrade public lighting operates for about
4000 h a year).
About 70% of the consumed electricity
(~17 million kWh) is produced in thermal
power plants, which emit CO2 and other
greenhouse gases (sulphur dioxide, nitrogen
oxides and methane).
Ingineria Iluminatului 2012; 14, 2: 27-32