Would one LED be dimmer than the other as I suspect, with the other drawing a larger share of the current?
And come to think of it... If I were to try to measure the voltage drop across the LEDs, what would I read, with the anodes and cathodes connected like that? Would it be the average of the two voltage drops? Or the smaller of the two?
If the two LEDs are exactly the same type, then you may find that they share the current quite well. I once took apart a toy light sabre, and it had 16 green LEDs connected in parallel, with no resistors to balance the current. Amazingly, the brightness was fairly uniform across all the LEDs.
These LEDs are attached to a constant current driver. So there's no worries about that happening.
Quote from: scswift on Dec 30, 2012, 10:24 amThese LEDs are attached to a constant current driver. So there's no worries about that happening.He's got you there, Mike...
And there is some kind of reflection issue in the data lines when I have more than six modules in series, where the LEDs on the last few modules will be messed up.
Well only because he is running the LEDs at less than half the rated current so there is little point in having two anyway. The fact remains putting two LEDs in parallel is just plane stupid design.
It may not be efficient to put two LEDs in parallel attached to a constant current source only capable of sourcing 20mA, but the consideration here is for aesthetics, not efficiency.
TI's datasheets make no mention of any special layout
Also, I'm not familiar with buffering, but if by that you mean put another chip on the line, that seems like it would be way too expensive,
Assuming adding buffering is too expensive,