The rainbowgun. It's not really a fire trick, but it looks so much cooler with smoke. Also I'm not sure if it's flashlights, photography, or lightpainting. A little of each. If you expose it wrong it's just white, if you hold it wrong it's a smear, and if you build your light wrong it sucks. So I put it here because you're the same people asking about it.

Take any light - the brighter the better (Halogen spotlights work well) - and put a rainbow filter on it. You're done! Now stand in a tunnel and, holding it very still, take a slightly underexposed shot. Adjust from there. For those of us without gel sample packs, you'll need:


A bright light. This can be an LED light. Mine is the Black&Decker V-2million spotlight, it's a car headlight bulb (high and low beam) with a 12v battery inside.


Clear packing tape and sharpies. Stick to bright colors - Bright red, Orange, Yellow, the pretty green (neither puke nor olive green), royal blue, and either purple or, surprisingly, pink.


Stretch packing tape over, color a rainbow. Do it again, and maybe a third or even fourth time. The brighter the light, the more layers you can do. As you add each layer, make sure the colors line up - you're tracing because you're coloring tape stuck to colored tape. More layers makes better colors, but it also cuts output. If you have a dark room in your house you can test a long exposure after each layer. Once you're happy, put a final layer of clear tape over to protect the sharpie ink.


The mystical rainbowgun always comes with orbs. I'm lighting it with a flashlight so you can see the colors.


Looking into the light. You can see the wear and tear on the colors, I'll be replacing this soon.


Shiny targets do not come out rainbowy, they come out overexposed. Here is the rainbowgun's pattern. Concentric rings are interesting but they don't come out as well in most pictures.

You can build this as a removable filter - all you need is a place to stretch the tape, and this has to stick on the light somehow. Even small LED flashlights can be rainbowized - bottle lids are a good size.

Notes:

You're putting a patterned filter very close to a reflector, which encounters some problems. The rainbowgun does not cast pure rainbow because the light hitting the reflector goes through multiple colors before it makes the final beam - mixing colors makes white. So the spill (photons going directly from the bulb to the filter) have vivid rainbowness, and the focused spot has a bit of rainbow power.

Don't melt tape. It's not extremely toxic, but it's an unfortunate mess to clean off a spotlight after it's done.

Gel packs would probably work better, but I was in a hurry and this turned out pretty well. Thoughts?

The same thing can be done with pure colors - that's why removable is good. But filters only take away colors. White LEDs mainly put out blue and yellow, so a red filter on one would be sad. Magenta is nice, so is green or blue. On an incandescent light you can pick any color filter with no trouble.

Fantastic! I was wondering how the mysterious Rainbow Gun worked. Now we just need a second one... Just sayin'

It's a pretty awesome Soulstealer 9000 you've made yerself there Apps!

After talking with Trap, I found a real use for the aspheric lights - they cast pure rainbow power. One problem with them is that zooming the aspheric will cut out the edges of your rainbow filter. Plan accordingly. I used a bottle cap with the center cut out to hold the tape.


Aspheric flashlight. Classic bubble-shaped lens on the front.


Casts pure rainbows.