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(11) | EP 1 079 667 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Lighting control device |
| (57) A lighting device and control means therefor is disclosed. The lighting device consists
of a plurality of White LEDs (WLEDs) provided in separate chains all connected parallel.
A small number of WLEDs is connected in series in each chain, and a number of such
chains are wired together in parallel between a pair of voltage lines from which current
is drawn. Current measurement and adjusting means is provided firstly between a high
voltage line and all the parallely connected chains, and secondly in each chain. Each
current measurement and adjusting means is controlled ideally by a microprocessor
which monitors both the total current drawn by all the chains together and also the
individual currents flowing in each chain. WLEDs have a tendency to fail when subjected
to sudden current increases, and also when operating at extreme temperatures as temperature
affects the operating characteristics of diodes in general. It cannot however accurately
be predicted whether a particular WLED will fail in open or closed circuit and the
invention provides a means of mitigating the effect of failure of one WLED on those
which remain functioning in the circuit. The control means immediately increases or
reduces the total current flow to all the chains depending on whether a WLEDs fails
in short or open circuit. The control means also detects operating temperature and
user light intensity requirement and adjusts various currents accordingly. |