It’s a 3mm red  LED. It has a typical forward voltage of 2.4v and a rated forward current of 20mA. A red LED is a semiconductor device and it is used as a indicator lamp in many device and are increasingly used for another lighting. They are used in  wide range of application such as TV set, monitor, Telephone, computer, Project panel for indicators. SPECIFICATION Diameter  3 mm Glow Colour Red Forward voltage 2.2 V to 2.4 V Peak Reverse Voltage 5 volts Lens Color Red Wavelength 630-635nm Viewing Angle 60° Country of Origin China