When testing I start with everything tightly connected, use variable voltage setting and bring it up slowly until I hit my target current. Then record the voltage reading.
Weezard, I don't want to have a semantic-induced disaster here, so: The instructions I got with my Mastech are worded this way:

2.2 Operating Procedure

2.2.1 For constant voltage mode adjust controls 3 & 4 clockwise....
2.2.2 For constant current mode adjust controls 5 & 6 clockwise....
2.2.3 For restricted current protection mode switch on the power...

I can type the whole sections out (they're short) if this is different than the instruction book you got with your Mastech. They don't discuss a "variable voltage" setting per se, and following their procedures outlined above has been costly. Sorry to be such a dolt, but could you outline your start-up procedure to include "knob positions" before power-up, or otherwise reconcile your expression "variable voltage" to Mastech's "constant" or "restricted" modes?

I know following their instructions exactly will spike the leds. My electronics training consists entirely of having worked as a janitor at an audio shop in the early 70's (after I ran out of $ for school) and looking over the tech's shoulders as they worked and eavesdropping on their techie conversations. These guys were not too keen to share any info, and trying to read books (pre-internet) to figure out what they were talking about was really frustrating. I understand what pots and resistors do, and have been zapped by a few caps that were storing up a present for me. I have used tiny leds for years as indicator lights (with a drop-down resistor) but these high-power emitters are a different beast for sure.

I can do the simple math involved with calculations involving Ohm's law, but sometimes I'm baffled about which terms to plug into the equation, like when there are multiple values (2.2V here, 1.2V on the other side of a resistor, etc.)--which one gets plugged into the equation? :i feel stupid: (if that makes any sense?)

Thanks in advance. I think if you can explain this so I can understand it, I can eventually do a tutorial / build log so anybody that can solder can also do it. There's quite a few folks following this thread, unproductive as it has been to this point, so I think the interest is out there.

Seems like commercially produced led grow lamps are not getting any cheaper (contrary to what usually happens with tech stuff), and the Procyon was the only one that was honest about what components were used. Unfortunately, you risk paying high dollars for glorified china panels if you don't assemble the components yourself. There are a lot of profiteers out there jumping on the led bandwagon, but the fact that they're overstating their products' capabilities is causing lots of folks to discount led growing altogether.