I was just thinking, it should be easy to put a twisty head on both ends of a flashlight with some pill wiring change in the “tail end”.
1xAAA double headed twisty, small and narrow as possible, one end white, one end red with knurling to detect which is which by feel.
What an interesting idea , Danglerb !
Great idea, for those times when we don’t know if we’re coming or going 
Darth lerb 
Except …… serial circuit, means current needs to flow at both ends for either end to light up. Normally that means tail cap is closed, either via switch or always in a side or head switched twisty, and light turns on when pill device closes the circuit and current flows through the LED.
My “current” thought, is that it won’t work.
Each end needs two contacts. A constant contact for driving the other end and a switched contact for its own end. The constant contact would be pushed against the driver board on that end when the head is screwed down, and somehow pushed away to break contact when the head is loosened. There would have to be another conductor besides the battery tube to carry the other voltage to the far end. It is more complicated but not impractical. I don’t think I can do it at home easily.
The red LED generally is going to be VERY low power, like 20 ma, so the conductor could be very small flat wire, but that still leaves the issue of how to make a connection if the tail unscrews for battery access etc.
Pulling back from the details, the goal is a practical red LED in my pocket for night use that doesn’t mess up my night vision or disturb others. That means it needs to be able to reliably be selected without activating any of the white modes, and be both small enough for EDC along with the combined use so its always there even if rarely used.
Maybe make the body out of plastic, then plate so inside is - and outside is +
:d
I gots to say, that’s just freaking cool.
The simplest way to make a double headed AAA light for occasional use would be to find an appropriate metal flashlight body with no anodizing or coating on the inside of the tube that both heads could screw onto.
I would use two 10180 or two 1/3 AAA cells back to back, if you get my meaning.
Then just jam a metal spacer in the middle of the tube, i would use a scrunched up & compressed piece of aluminium foil for testing this and getting the spacer the right size.
There you go, no mucking about with wiring or drivers etc.
The only problem is making or finding a flashlight body where the head can screw on both ends.
I can’t think of any readymade AAA lights like that, any ideas?
The $2 3W Police / Camp lights. Both ends are threaded I think the same, they allow tricks like 2x extensions. Ah, but they are AA not AAA.
For those of us that use P60/D26 lights
5mm LEDs, small amount of light, good for complete darkness/camping/astronomy:
http://www.amazon.com/Rigel-Systems-Skylite-Switchable-Flashlight/dp/B000B5AQL2
(not exactly what you asked about, but gives the same result).
Two very small cells would be simpler but not as nice as having the full capacity available in either color. I don’t see that it need have low output, except for the shortage of good AAA sized drivers. A flat copper strip could be thick enough to have low resistance without taking up much space. Two of this driver http://www.dx.com/p/ak-007-0-8-1-5v-3-mode-circuit-board-for-flashlights-11-9mm-50526#.VBc5VRbOWRY would take up some space, so one might settle for one mode each end with two Nanjg 102s. Or it could be direct drive 10440 with the thicknesses of the conductors chosen for the desired outputs. Or two BLF Tiny 10s. These give 350 or 380 ma on high or a multiple of that by stacking the 7135s, and full mode control, but they also require space, a second layer to make battery contact, and are hard to assemble. I like the Philips Luxeon deep red for minimum night vision interference.
The Rigel may be a bit large, more lanyard wear than a pocket light. In the same category is the below linked to Smith & Wesson light.
The dual switches are far enough apart so that choosing the wrong one appears to be unlikely.
The two buttons is nice, but it is bigger than we were thinking of. I don’t think both leds at the same end can give good patterns for both colors.
Peak led solutions did that years ago.
Double-ended Logan / McKinley
If your end goal is simple a light that can put out white and a small amount of red light on demand I have something for you! I’m using one or two red
XB-D’s mounted in small holes in the side of the reflector for what’s known as “dim to red” where the lowest level switches over to red (another neat feature is that electronic switch lights will be able to flash the red emitter as a locator beacon.)
That sounds very good, any more details?
What started me on this is that I have some of the original promo LED lights from HP, 2xAA with first gen red LEDs, and they are really nice for working at night when you don’t want to lose your night vision. Much more recently I bought a $6 headlamp that is hi/med/red led, and again its great for walking in the dark with just enough light.
BTW as a preference starting with red and ramping up to white, or mode switching to white would skip a blinding white first, otherwise I would be covering light to start until in red mode.
That looks nice, and it looks like what we halve been discussing. Is it really a two ended twisty? Is one end red and one white, or would that require a small mod.? Are they available?