Ampere! 9A driver from PCB Components (red circle: sense resistor) Formula: desired current (A) = 0.05 (V) / sense resistor (Ohm)
This is the source of inspiration of my torch, a torch built by Prof. Horst Grunz; see also http://www.uni-due.de/zoophysiologie/aa.guests/FluorescenceHigh.pdf on page 23 and http://www.diveinside.de/DiveInside_Suesswasser-Perlen_web_45.pdf on page 46.
