This is one of those questions that never seems to go away, but I don't recall ever hearing a definitive answer.

Does it matter which lead (positive or negative) of the LED you attach the resistor to?

Attach the resistor to the positive lead of the LED. It does not matter which direction the ends of the resistor go.


Geminibuildups
www.geminibuildupstudios.com

Functionally it doesn’t matter if the resistor is in series with the positive or negative lead of the LED. If there’s much heat dissipated in the resistor though it’s better to connect it to the non-substrate lead of the LED. To determine which lead is the substrate look at the LED from the side, the substrate is attached to the land that extends into the middle of the LED from one of the legs. Typically this will be the negative lead, but in some high output reds the substrate can be the positive lead.

Thanks, guys.

While prepping the interior lighting of my Moebius Flying Sub I accidentally soldered resistors to the negative lead of three of the LEDs I'd planned on using. Just for the heck of it I temp-wired everything up to a 9V just to see what would happen, and after 5 minutes all the lights were all working fine, with no ill-effects I could detect. This made me wonder if perhaps it didn't matter which lead was connected to the resistor after all.

Just to be on the safe side, and in the interests of uniformity, I'll probably make replacements for the lights in question.

I usually solder to the positive lead. If the led shorts out, it limits the current and may let the rest keep functioning.

As well, if it's on the negative, and you short the negative lead to ground before the led, say goodbye to the led real quick!

Electrically it doesn't matter. However I always solser the resistor to the positive lead as a way of keeping track of which lead is which.

ditto on the "it doesn't matter."

I know intuitively you would think the resistor should go "before" the LED in order to "protect" it, but it's more like plumbing where the flow of water is restricted no matter where the restriction exists, and it's the total "flow" (current) of electrons that counts.

jwrjr's suggestion, just to be consistent, makes as much sense as any, but you'll find some applications where it's convenient to do otherwise...

Thanks again, gents. This is one lighting issue I won't have to trouble you with in the future. The positive lead is the one to which I'll be connecting my resistors here on out, if for no other reason than consistency.

I'm with James,
I always solder to the positive for no other reason than to keep them straight. Especially helpful if you use heat shrink