Look here for original web page that these notes come from with more discussion about the regulated version
R1 is the throttle valve.  As it gets larger, the LED current gets smaller.  The components can vary quite a bit.  Exact matches with the circuit diagram above are not necessary.  The Schottsky diode and capacitor can be deleted.  They're used to smooth out the output.  Try using a 5k or 10k trim pot for R1 so output current can be adjusted.  Multiple LEDs can be put in parallel if their voltage drops are about the same.  Using a small resistor with each LED helps even out current distribution.

Coil winding detail

Modified One Transistor Design for Multiple LEDs

Regulated Version

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