Typically, one side is flat and has a shorter lead to mark the cathode side, as they must be inserted in the right direction. The flat side corresponds to a straight line segment on one side of their circuit diagram symbol. In AC applications where the current exceeds the breakdown voltage, they can be protected by placing a second one in inverse parallel. Although they are much more reliable than incandescent sources, (*) they can still be damaged by a sudden change in temperature, which might 
Typically, one side is flat and has a shorter lead to mark the cathode side, as they must be inserted in the right direction. The flat side corresponds to a straight line segment on one side of their circuit diagram symbol. In AC applications where the current exceeds the breakdown voltage, they can be protected by placing a second one in inverse parallel. Although they are much more reliable than incandescent sources, (*) they can still be damaged by a sudden change in temperature, which might cause cracks to form in the epoxy resin in the packaging. Aluminum gallium arsenide is used in red and infrared ones, while blue ones require a quantum well and are thus more expensive to produce and rarer. The color of the plastic casing does not significantly affect the color. FTP, name this electronic device which exhibits electroluminescence and allows current to flow in only one direction.
Typically, one side is flat and has a shorter lead to mark the cathode side, as they must be inserted in the right direction.
{Light}-{Emitting Diode} (prompt on {diode})