In my previous piece about playing with copper tape and wire glue and silver-ink pen, I was having trouble figuring out a way to hold a surface-mount LED down and get it electrically connected at the same time. Mashing copper-foil tape onto the sides of the LED works, but it’s hard work. Gluing the LED down and then attaching foil or drawing on a silver-ink connection doesn’t really work reliably at all.
So I did some more experiments and found a) that drawing the silver-ink line first, then putting down a dot of wire glue at each contact point and dropping the LED in the middle works just fine once the glue dries. And b) doing the same thing with copper-foil tape works fine as well.
Which brings me to c) by way of a little basic electronics: an LED in the conductive, light-emitting state does not have any resistance. It has a voltage drop across it, but once you’ve got that much voltage or more across it, it will just suck down as much current as you’ve got. Wire glue, on the other hand, has quite a bit of resistance: maybe a few hundred ohms for a few millimeters. So c) lay down your copper-foil tape with a little gap where the LED will go. Dab some wire glue across the gap. Plonk the LED down and make sure the glue squelches out around the edges. When everything is dry, current will flow through the wire glue, but it will be happier to flow through the LED. Solid physical attachment, reliable conductivity.
Yes, your greeting card or mask or whatever it is will draw a few milliamps more current and have a slightly shorter battery life. Do you care?