Spectral fires burning bright
Chasing shadows in the night
In essence, a fire effect is achieved by simply soldering a bunch of flashing LED's in parallel and hooking them up to a battery with a switch in between. SpookyFire's version used solely red LED's. For my model, I used:
This gives it more of a fire feel, but it doesn't have the cool 'spectral aura' that SpookyBlue's version has. I'd say that if you want it to look like fire, add the yellow LED's, but if you want it to look like supernatural evil smouldering, use only red LED's.
Here is a video clip of how the SpookyFire looks with yellow thrown into the mix. The video, as usual, doesn't do the effect justice, as it is a subtle lighting effect that simply cannot be captured on video easily.
You'll also notice in the foreground an all-green SpookyFire blob in the front skull, something I don't particularly recommend. The flashing green LED's look cool, but they throw off an almost white light, so it doesn't have the eerie green glow you might expect. (The interior of that skull is painted green, so don't let the green color fool you!) Especially, don't mix green with yellow LED's, because the yellow will vastly overpower the green, even at a ratio of one to four.