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
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