One corner is notched, with the leads pointing down, and the notched corner to the lower right, the top two leads go to positive, lower got to negative. Would strongly suggest a constant current source, instead of a resistor, they fry easy. Least the ones I get from Hong Kong do. If you run them as specified, they work well. Should also share a past experience... Before I got the notch thing, I used a fairly dead 9 volt battery to briefly check which way to plug them in the PCB. Mistakenly grabbed a fresh battery once, the lense blew off, bounced off the 8' ceiling with considerable force. Figured you should know, or you might put out an eye or something.