TLDR:
I wanted to determine how much the voltage across an LED strip can change before color aberration becomes noticeable to the human eye. This seems to be a drop of around 1.7v from a 5v rail.
Introduction:
Based on our current draw tests we are probably going to be using 14-16 gauge wire for our 5v rail and ground. We know from our previous Hell Lighting setup, that the voltage drop across 20 meters of 16 gauge wire can be pretty significant, on the order of 0.5-1.5v depending on the pattern being displayed. Since we want the color recreation of our LEDs to be pretty consistent along the length of the hallway, I decided to get some data on what kind of voltage drop leads to a noticeable difference.
Methods:
To get an idea of how quickly color drops off with voltage, I spliced a few of our sample strands together and wrapped them around a piece of metal that, I assume, began life as a table leg (though at present it smells suspiciously like mortars). In any case, its circumference is pretty close to an even multiple of the LED spacing so it makes for a nice clean pattern (see photo). Our experience when we put up Hell Lighting 1.0, was that color aeration was most noticeable with the system running at full brightness on each LED (pure white).
Once the system was set up, passing moles were flagged down and asked where on the pole they first started to notice color change. Pretty subjective as tests go, but since we only really care about subjective user experience that's fine.
Discussion / Results:
With the strip running at full brightness, people pretty consistently pointed to an LED somewhere between the 3.4v and 3.5v as the first place that color change became noticeable. When I lowered the strip output to 40% color change along the strip became much less noticeable, though the voltage never dropped below 4v so it is hard to say if the effects would have been noticable at lower voltages.
The strips themselves seem to get to this point after about 80 LEDs (2.6m). So if we connect the strips to our 5v and GND rails every 2m we need to hold the variability of the 5v rail itself to under .4v if we want to keep the colors consistent.
Links:
Bonus Image, there are probably some interesting patterns you could run on a cylindrical display.