Page 11 - GRECHI Lighting LED
P. 11
DIMMING
METHODS
Metodi di
dimmerazione
Dimming is the process which reg- mediate application of an input. All of dimming is based on the possi-
ulates the flux emitted from street the interventions of modification bility to reduce the light emission
light, reducing the power that it ab- that are necessary as a direct con- when the concentration of traffic on
sorbs in a proportional manner. This sequence of a cause, without being the roads is lower.
represents only a minimal part of programmed beforehand, are in the According to UNI 11248 regulations
the functionality which a manage- category of direct command. An it is possible to attribute different
ment system can offer. example of direct command can be categories of lighting techniques to
The LEDs can reduce their luminous represented by the manual interven- a chosen road, which have perfor-
flux by using two different technol- tion of an operator who is dimming mance requirements that are low-
ogies: or increasing the light intensity due er than those originally identified
P.W.M. pulse with modulation to an unforeseen necessity. by the project designer, evaluating
This is a system that modulates the some influential parameters which
distribution of current to the diode Programmed curves are necessary to define the anal-
by the cyclic repetition of impuls- The programmed curves of dimming ysis of risk. The aim is to “guaran-
es so as to generate a sequence of represent more complex groups of tee the maximum efficiency of the
lighting up and switching off. When control, as they link the state of dim- lighting plant in contributing to the
the periods of switching off are ming to the time of day. safety of the users (…) at the same
longer than the periods of lighting A sequence of dimming commands time minimizing energy consump-
up, the flow emitted over the period are progressively sent over the pe- tion, the costs of installation and
will be lower. The frequency of the riod of time during which the lights management and the impact on the
impulse cannot be noticed by the are turned on, in this way program- environment.” Among the different
human eye. ming of the light emission can be influential parameters mentioned in
Analogical made beforehand. If we trace out a the regulations is the reduction of
The analogical system reduces the graph of the values of light emission traffic flow in respect to the max-
current value entering the diode; that are linked to the time of day the imum registered traffic flow; and
when the current emitted is less, “dimming curve” is obtained. more specifically, the regulations al-
the power absorbed is less and the The pre-set curves are most suitable low the declassification of a lighting
light emitted is less. In order to be for programming self-dimming light technique by one category when-
dimmed the LED cards must be fittings; that is to say, without any ever there is a 50% reduction of the
necessarily prepared to translate external connection. traffic flow during the night and the
and branch out to the single diodes They can however be installed on declassification by two categories
one or both of the above mentioned master control centres, and succes- when the traffic flow is reduced to
systems. All the LED diodes can be sively branched out to the intercon- under 25%.
dimmed and, if the card on which nected light fittings. If the curves are The evaluation of the reduction of
they are mounted is prepared to re- set on on-board systems, the timing traffic compared to the time of day
ceive the dimming command, they will always be the same as the nat- must be carried out by the project
can be set on any configuration that ural time, which refers therefore to manager for each specific case un-
is required. The methods used to natural midnight; if the curves are der examination and following the
control dimming of a LED can be set on a master control centre, and if report on the analysis of risks (see
grouped in two large categories: they are remote controlled, they can UNI 11248 paragraph 7), the project
direct commands and programmed also refer to the real time. manager will be able to establish the
curves. time at which it is possible to apply
Direct commands Refer to diagram 1 declassification of category and the
A direct command foresees the im- time when it is necessary to return
How to calculate the dimming to the initial situation. Grechi Light &
values Energy will propose the percentage
Programming of the pre-set curves
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