Another option would be to go with a constant current source. Let the voltage change as needed. You will always have 20mA (or whatever amperage you design for) running through your LED's. I'd still recommend strings of 3 in series and six sets of 3 series.

 

Thank you. CHANGES: 5V and no buck converter.View attachment 290189

18 100Ω resistors in parallel has an equivalent resistance of 5.6Ω. The result is supplying 300mA to each LED which is rated at 20mA. 15x more current than they are rated for. You’re lucky if you haven’t destroyed several LEDs. As many people have stated, you need one resistor in series with one LED. Then wire all the resistor/LED pairs in parallel.
If they’re modern LEDs, 100Ω should work (running the LEDs at 6mA). If you want them brighter, try 82Ω resistors (but this runs them at 21mA, a bit more than their assumed 20mA maximum)

 

18 100Ω resistors in parallel has an equivalent resistance of 5.6Ω. The result is supplying 300mA to each LED which is rated at 20mA. 15x more current than they are rated for. You’re lucky if you haven’t destroyed several LEDs. As many people have stated, you need one resistor in series with one LED. Then wire all the resistor/LED pairs in parallel.
If they’re modern LEDs, 100Ω should work (running the LEDs at 6mA). If you want them brighter, try 82Ω resistors (but this runs them at 21mA, a bit more than their assumed 20mA maximum)

How are you coming up with 300 mA?

The resistors in that circuit play no role in establishing the current in the LEDs (unless they draw so much current that the supply voltage starts sagging). Each LED is being placed directly across the supply output terminals. How much current each is pulling is anyone's guess over a wide range of possible values.

 

How are you coming up with 300 mA?

The resistors in that circuit play no role in establishing the current in the LEDs (unless they draw so much current that the supply voltage starts sagging). Each LED is being placed directly across the supply output terminals. How much current each is pulling is anyone's guess over a wide range of possible values.

Oops, I misread the drawing. I based my comment on thinking the 18 resistors in parallel were in series with the LEDs. I was wrong.

 

The multi-series idea is interesting, but I've prepped for redoing completly in LED parallel, dropping the grouped resistor idea. I'll just put each resistor next to each LED. Thank you all for your help. I feel quite the idiot for thinking I had a great idea, but bass-ackwardsing it.

 

I did it ther old fashioned way and put a resistor with each LED and it's beautiful. I think it was actually less work than grouping th resistors (incorrrectly!) Works great. Thank for all the help!