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.

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