ingineria iluminatului - Journal of Lighting Engineering - Prof. Florin ...

H C. ALBU, Liisa HALONEN, E TETRI, F POP
used in private office rooms concludes that
by using an occupancy sensor 20÷26% of
energy savings are made and by using
automatic daylight dimming controls
savings of 21% are achieved, compared to
manual switching [8]. A different study
conducted on open-plan offices shows
reduction in electric energy consumption of
35% if occupancy sensors are used alone,
20% for light sensors and 11% individual
dimming. Also, if all three controls are
used, a reduction of the average daily peak
power demand of 65÷70% is achieved,
compared to a conventional lighting system
[9]. Electric energy savings are highlighted
for an office building in [10], where
different rooms have different lighting
control techniques employed. The average
energy consumption savings of 40% are
achieved if occupancy and daylight
dimming control are used and 22%, if
occupancy and manual dimming control are
employed, compared to a room without
dimming and occupancy control.
One direct effect of using light dimming
controls is a decrease in the power factor, as
shown in [11]. Here the results of testing the
dimming effect on eighteen ballasts, used for
T5 fluorescent lamps of 28 W, 49 W and 54
W are presented. The decrease in the power
factor is attributed to the increase in the
Total Harmonic Distortion of the Input
current waveform (THDI) during dimming.
2 Office characteristics
2.1 Light requirements in office buildings
The standard EN 12464-1:2002 [12]
recommends that “adequate and appropriate
lighting” should be provided in buildings, in
order to “enable people to perform visual
tasks efficiently and accurately”. The
lighting requirements specified by the
standard are determined by the satisfaction
of three basic human needs: visual comfort
(the workers have a feeling of well-being),
visual performance (the workers are able to
perform their visual tasks) and safety.
For the majority of office work
activities, the illuminance required levels
recommended by [12] are set between 300
lx and 500 lx, with differences regarding
room designation. The Unified Glare Rating
(UGR) limits are set between 16 and 25,
depending on the room peculiarity. Also,
the standard recommends that lamps with a
Color Rendering Index (CRI) lower than 80
should not be used in interiors where people
work or stay for longer periods.
A study conducted in [13] shows that the
change in the correlated color temperature
(CCT) and illumination level is affecting the
visual appeal of a space in office buildings:
- 2000 lx was preferred to 500 lx for the
impressions of comfort, spaciousness,
brightness, and saturation evaluation;
- 4000 K CCT was preferred to 2700 K
for the impressions of comfort and
spaciousness, while 2700 K was suggested for
relaxation and the saturation evaluation.
2.2 Power quality requirements in office
buildings
A significant part of the equipment that
exists in office buildings (electronic and
computer devices) requires a good power
quality. At the same time, the same
equipment often causes distortion of the
voltage supply in the installation, because
of its non-linear characteristics (it draws a
non-sinusoidal current when supplied with
a sinusoidal supply voltage). Therefore,
6 Ingineria Iluminatului 2010; 12, 2: 5-22