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.

[caption id="attachment_164" align="aligncenter" width="500" caption="0603 SMD LED Anode Cathode Positive Negative"]0603 SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_166" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_161" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_160" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_162" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_167" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_163" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption] [caption id="attachment_165" align="aligncenter" width="500" caption="SMD LED Anode Cathode Positive Negative"]SMD LED Anode Cathode Positive Negative[/caption]