Which side of the pads under this xpl hi is the anode and which is the cathode? reflowing a black flat and i need to know cause i dont want to kill the led, i have 4 more if i make a mistake
Thanks
I always forget which is which…
So i test it with my digital multimeter, in the “beep” setting.
The LED will light up slightly with the red probe on the + and the black probe on the - .
Yeah, it’s a bit finicky…
Or you can just gamble and check the polarity the same way when it’s on the board, to determin which is which. :innocent:
On the XP-L you can see bond wires on the positive side, this doesn’t always hold true but it is on this one. Positive is anode.
Download the spec sheet on the emitter you plan to use and verify which pad is anode and cathode. The new Samsung LH351D has notches in the cathode side, the anode side is flush all around (no notches or other indicators)
Go by the data sheet for your emitter, it’ll show you and then you’ll know for sure…
At the end of the day it really doesn’t matter, if you put it on backwards it just won’t work, the emitter is a “diode” and current only flows one direction. If that happens, simply put your wires on opposite what the MCPCB says. 
This, 100%
Not quite. Diodes are specified with forward and reverse voltages, and will pass come current when reversed.
Cree claims that most of its emitters will only suffer damage if the reverse bias voltage is several times the standard operating forward voltage. This might be a problem with a constant-current switch-mode driver with a voltage limit set too high.
It doesn’t matter which way you orient the LED as long as you connect the leads the right way, but it’s best to follow the labels on the MCPCB. The black flat has the anode and cathode clearly marked on the pads, so just orient the cathode cutout mark towards the negative side of the MCPCB and connect the negative lead to it.
Anode = positive
I remember it cause A is the first letter of the alphabet and positive comes first
Anode = +
Cathode = -
eas, I hear what you’re saying, but I’ve built over 500 lights and never had an issue with an emitter that was hooked up backwards. And yes, I’ve mistakenly done it quite a few times, never blew one. So, at the end of the day… it doesn’t really matter.
That said, I don’t make it a practice to turn a light on for the first time in Turbo mode, always check with a bench cell to make sure the emitter is properly mounted before putting it in the light. And typically leave my lap pull bench cell discharged. (Sanyo FJ) So I recommend following some normal testing protocol before subjecting any new build to full power. May well save you having to endure magic smoke and all that good stuff…
(mostly from a shorted positive pad to thermal pad, things like that DO happen)
Or dont PANIC!
Positive Anode Negative Is Cathode 
Zozz? Is that saying it’s opposite? Do Not put positive to Anode and negative to Cathode? 
(Don’t, do not, a negative in front of a positive, see what I did there? )
Guys I did it, this thing is amazing!! Measured 300kcd and 700 lumens in the D1S, turned out great, focused on first try
Sweet Mike! Good job! 
Impressive output!
Makes me want to check into this Oslon black flat emitter, where can they be found?