Periodically I receive information about new products directly from manufacturers.
The latest one are LED 'bulbs' that run from 0.8V to 1.8. Yes, white too.
At the end of list, Part number starts with OBD3 :

----> http://www.optosupply.com/EN/product_list2.asp?sid=121&bid=158&i=2&pdid=2&

Enjoy.

 

Hello,

The "leds" will have some electronics in the base to work on the large voltage range.
This could be a buck/boost circuit.

Bertus

 

I have a Joule Thief flashlight (white LED) in my pocket that will run from a single AA battery. It must have .6 volts to start but it will suck the battery down to 0.1 volt if you accidentally leave it on.
These bulbs that you pointed out will make these flashlights cheaper and smaller because the Mfg. will not need to dedicate half an inch to building the oscillator circuit into the flashlight.

 

Yes, Bertus is correct. Big Clive posted how to make these on his website years ago:
http://www.bigclive.com/joule.htm

There's a bunch of interesting/fun stuff on his site.