I've been experimenting with some of these LEDs, and have just made a discovery that merits bumping this thread.
Having read this thread and been intrigued, I purchased a bunch of these
yellow 10mm diffused LEDs and have been running them on CR2032 batteries with great effect.
While they do run for a very long time (over 3 days) on a single battery, the brightness does drop off fairly quickly in favour of a softer, sustained glow. I tried combinations of adding more LEDs with little difference. I've left them in pumpkins on my desk for days, which is nice, but I couldn't help but wonder if a brighter/better solution was out there.
I was browsing Evil Mad Scientist's shop last week, when I stumbled upon this
Solderless Flickery Flame LED Kit, which I figured was worth a try. I picked up five of the kits, and have been testing two of them out. I am extremely impressed so far. They are they best alternative to a candle that I've ever seen. You'd be hard-pressed to tell the difference from the curb. They take two AA batteries, and I imagine the resistors makes it easier on the power draw. Here is a video of one in a small Michaels foamy, with one outside for ambient light:
I ran one for 5 hours so far and it doesn't seem any dimmer than the fresh one. The instructions are very clear and other than a little optional wire clipping, these go together like small Lego sets (5-10 minute assembly time). The LEDs in these kits are smaller than the ones linked above (they are probably 5mm), but are very bright. I tried swapping some of the 5mm ones out for the larger LEDs to see if it had an impact, but what comes stock in the kit seems to be optimized. The addition of red LEDs really helps add a little depth/realism to the candle effect.
The only downside to these is that it looks a little weird when you look down into the pumpkin and can see wires, breadboard, resistors, etc. (faux tea lights and Howlers are a little easier on the eyes when visible). I think it's more than worth it for the great effect.
Like I said, carves look bright/crisp/flickery from across the street. I'm glad I picked up five of these kits. I'll let you know how they perform and what people think this Halloween.
They also offer a
soldering kit version, which is more compact and a little more affordable if you have the tools to solder it together. I imagine this one would be a little easier to conceal within the pumpkin.