>>> Any suggestions will be considered.
>>
>> Why not using CAN bus?
>
> Because that would be rather heavyweight at each LED.

Yes heavyweight, but not nesessarily too expensive. I know CAN-enabled
LPC11C12 does not fit his requirements, but as its price is only
US$2.60 (in 250+) it can be a candidate in case 3 LEDs per unit.
http://www.futureelectronics.com/en/technologies/semiconductors/microcontro=
llers/32-bit/Pages/1035466-LPC11C12FBD48-301.aspx
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