ALLNET Brick'R'knowledge LED IR
The brick has two LEDs, a red one for control and an infrared (IR) light-emitting diode that cannot be seen directly, in our case approx. 900 nm. You can usually still observe it with a camera. Both LEDs are protected from excessive current flow by series resistors. They only light up when the diode is connected in the direction of flow, i.e. the current flows from the anode to the cathode. The LEDs require a minimum voltage in the direction of flow in order for them to light up, approx. 2V for both.