Effect Of Ageing On Lamps - ABB i-bus KNX Product Manual

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ABB i-bus KNX
4.7.4

Effect of ageing on lamps

© 2008 ABB STOTZ-KONTAKT GmbH
Planning and application
Every fluorescent lamp ages in service. The lighting power of the fluorescent
lamps degrades, i.e. a lower brightness is produced at the same control
value. This can even mean that the setpoint originally required can no longer
be achieved with maximum control. For this reason the lighting is to be
dimensioned so that the required setpoint brightness can be achieved until
the luminaries are routinely exchanged.
In principle the ageing luminaries have no effect on the control circuit.
If a lower brightness level is achieved due to ageing of the luminaries with
the same control, the Light Controller will continue to increase the level of
artificial lighting until the setpoint brightness is achieved.
However, it must be considered that the characteristic of the luminaries
changes with ageing. The characteristic has been determined during the
calibration procedure and is the basis for the control algorithm. In this way
it is possible that light control discrepancies result.
The following approach results:
The recorded characteristic of the artificial lighting is calculated with the
control value. Assuming that the lamp generated 30 % less light, the value of
the characteristic would be 1.33 times larger than the real value.
The Light Controller "thinks" that the daylight share is less than it is in reality.
For the Light Controller there is less daylight as compensation is required.
With a compensation factor of 30 (for the control algorithm 0.3) an
approximate reduction of the setpoint value by 10 % would be achieved.
The Light Controller would control to a level which is too dark by 10 %.
In concrete terms that would mean that a light control originally set by the
Light Controller to 500 lx will now only provide a brightness value of 450 lx.
Furthermore, the tolerances apply as described in the
Note
The burn-in time where the light may not be dimmed must be complied
with to ensure that the most stable possible luminarie performance is
assured. During the burn-in time which usually lasts between 50 and 100
hours, the luminaries must be operated at 100 % brightness.
The burn-in time of a luminaire can be obtained from the manufacturer.
Technical data.
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