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I'm trying to dim a light fixture with the DALI protocol. It functions quite fine but when the dimming gets low two thirds of the LED:s turn of. Why is this?

Is it because the voltage forward gets to low to support all the LED:s? The driver that is used is constant current so it should be able to supply the voltage?

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  • \$\begingroup\$ which third do you prefer? What are you not telling us , that we need to know about the luminaires \$\endgroup\$ – Sunnyskyguy EE75 Sep 1 '17 at 13:25
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Check to make sure you have the correct LED board/lamps for the driver - drivers are designed only to work with a certain set of LED boards or lamps, and if you use them outside the specifications, odd things can happen like this, or spurious lamp fail detection, or flashing behaviour.

But if the LED board is matched to the driver and this still occurs, it is very unusual behaviour and you may have to contact the manufacturer to find out why this is happening. Whilst there are strict requirements for DALI curve accuracy and monotonicity, it doesn't specify evenness of light across the fixture. It is just a poor quality fixture if the diffuser is insufficient to hide the fact that some LEDs go off at low levels.

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  • \$\begingroup\$ I contacted the manufacturer and they acknowledged the error. Thanks for the help! \$\endgroup\$ – TheOne Sep 5 '17 at 6:23

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