Calculations for the UV LEDs
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The goal is to get a cheap simple LED driver. 

Material:

- A 18 V power supply is used.
- LEDs with 3.3 V forward voltage and a max. forward current of 30 mA are used.

18 V / 3.3 V = 5.4545 

So 4 LEDs can be put in a row. That means roughly 4.8 V have to be wiped out. Taking a 200 Ohm resistor results in 24 mA.

P = U * I 

So the resistors have to be able to take 115 mW. This is fine with every standard resistor. The risk with this technique is, that the foward current differs a lot, which results in another current going through the LEDs. So a better driver should be developed at some point. 

48 LEDs can be taken, which will result in ~1.2 A. As the power supply can deliver 2 A this is fine.