Intro: 1,5V to LED Voltage Converter A.k.a. Joule Thief
This is a schematic I accidentally got working. I was experimenting an idea to get a LED PWM on a 1,5V using a astable multivibrator to drive inductor and use its magnetic field collapse to light up an LED in rapid short pulses but I got more than I bargain for and the LED lit up with high frequency in 10s of kHz range - pretty much like a Joule Thief circuit. You can get parts from old CFL to build this, the capacitor capacitance is not critical, although you can find 22nF (223) and 47nF (473) capacitors in any CFL electronic ballast, I even tried two 1,2nF high voltage capacitors used to turn on the tube between two filaments that worked well on this circuit but the LED was little bit dimmer, the inductor is 1,3 to 3 mH range, few turns on a toroid doesn't work on this, but the ballast and some bobbin type filter inductor from CFL does well, but test the pinout and condition of the transistors before reusing these, as sometimes the pinout on these (13001, 13002, 13003, 6823D) is base-collector-emitter instead of emitter-collector-base and sometimes the transistors die during bulb EOL. So this is a share of the result, you can use this schematic to build your own version. CC-BY 4.0 - Attribution (use permitted).
The transistors on the schematic is 13003's, but any NPN should work. You can use PNP transistors also, but you need to reverse the power supply and the LED.