There are three ways to tell which side it positive or negative on an led in this fashion:Look at the long leg, that is positiveThere is usually a side or part of the led that is flat, that side is negativeIf you look inside the led you can see the larger side, which is also negative
led polarity
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Polarity Guide of 0402, 0603, 0805, 1206 and most all smd leds
This guide will tell you how to tell the polarity (positive/anode and negative/cathode) of leds. Most often if you can not see any of these markings, a small notch or dot will indicate the negative side of an led. This also goes for markings on a board too.