Using the FET DD drivers you first have to determine how much current the led can tolerate best case scenario and for that I look it up in Djozz’ tests he’s done a great job of crash resting an incredible variety of emitters. Having the led mounted on a direct thermal path (DTP) copper star is critical for any use approaching or exceeding max current specs. The use of DTP mcpcb’s allows us to do this because of their exceptional ability to wick heat away from the emitter. After looking up that info I decide where along the current/voltage/output curve I want my light to play. Matching your cell voltage to the voltage readings to the right will tell you what kind of current you can expect to deal with and a ballpark for output. 7135’s allow for quantum increases in current (in 350 mA or 380mA amounts) and FET DD drivers deliver whatever current can be pushed by the cells for a given led Vf.